Fennel seed (the dried fruit) and fennel tea. The fruit is the part used.

Herbs & Botanicals · Herbs · Kitchen seed and tea, with low-certainty evidence for infant colic, IBS and period pain, and clear estragole safety limits

Fennel

Q: Does fennel help with infant colic?

Possibly a little, but the evidence is low certainty. A fennel oil emulsion beat placebo in one trial of 125 infants (colic gone in 65% versus 23.7%), a chamomile, fennel and lemon balm extract cut crying time in another, and a pooled result of three fennel-containing trials found about 72 minutes less crying a day, with a very wide range. Reviews call fennel promising but say most trials have high or unclear risk of bias. Talk to a paediatrician first (see the next question).

Q: Is fennel tea safe for babies?

The EU herbal committee does not recommend fennel fruit preparations in children under 4 years because of lack of adequate data, and limits use at 4 to 12 years to short courses with an estragole cap. Small colic trials reported no side effects. There is one case report of early breast development in a 12-month-old after months of daily fennel tea, and some infant teas have high estragole levels. Ask a paediatrician or pharmacist before giving any fennel product to a baby.

Q: Does fennel help irritable bowel syndrome or indigestion?

For IBS, one 30-day placebo-controlled trial of capsules combining curcumin and fennel essential oil found better symptom scores, but fennel was not tested alone (low certainty). For indigestion no trial tested fennel alone; one open study used a seven-ingredient supplement. Lab work suggests fennel can relax part of the stomach.

Q: Does fennel ease period pain?

Many small trials, mostly from Iran, found less period pain with fennel and a similar effect to mefenamic acid, but results across trials differ widely and Cochrane rates the evidence for all supplements in this area low or very low. One trial found ginger worked better than fennel. Fennel capsules or extract may cause heavier bleeding in some women.

Q: Does fennel help menopause symptoms?

Results are mixed. A 2021 meta-analysis of two small placebo-controlled trials favoured fennel, but a third placebo-controlled trial found no difference because the placebo group also improved. Fennel alone did not clearly help sleep or mood. The one trial that measured blood oestradiol did not show a rise. All were small trials from Iran.

Q: Does fennel increase breast milk?

We do not know. Cochrane says it is very uncertain whether fennel (or fenugreek) improves infant weight, and milk volume results could not be combined. A safety trial of a fennel-containing tea in 60 breastfeeding mothers found no adverse events but did not test milk supply. The EU says fennel fruit is not recommended during breastfeeding.

Q: Is fennel safe in pregnancy and breastfeeding?

The EU herbal monographs say safety has not been established and use is not recommended in pregnancy or breastfeeding, partly because of the estragole limit (below 0.05 mg per person a day). Fennel extract caused birth defects in pregnant mice in a study cited by the EU. LactMed says anethole passes into breast milk and that excessive tea seemed to cause toxicity in two newborns. Ask a midwife or doctor.

Q: What is estragole and should I worry about it?

Estragole is a minor compound in fennel oil that causes DNA damage and liver tumours in rodents at doses far above human intake. The EU says exposure should be kept as low as practically achievable and, in 2005, concluded that short-term adult use at tea doses does not pose a significant cancer risk. Margin-of-exposure studies find a low priority for adults who drink one cup a day, but not for children if use continues long term. The amount varies hugely between products, and the oil is far more concentrated than tea.

Q: Is fennel a phytoestrogen? Is it safe with breast cancer or hormone treatment?

Fennel is often called a plant oestrogen. In lab cells, a breakdown product of anethole bound the oestrogen receptor and made breast cancer cells grow, and estragole and anethole raised oestrogen in a cell model. In people, one trial found oestradiol did not rise with fennel seed powder, but fennel brought on bleeding in women on a hormonal injection. The EU does not list hormone-sensitive conditions as a contraindication, but if you have an oestrogen-sensitive condition or take hormone treatment, ask your specialist first.

Q: Does fennel interact with medicines?

The EU monographs report no interactions, but very few have been studied. A rat study found an aqueous fennel extract cut ciprofloxacin absorption (peak level down 83%). Fennel produced bleeding in women on a depot contraceptive injection. No study of fennel with tamoxifen or other hormone treatments was found. Tell your pharmacist about fennel supplements or regular fennel tea.

Foeniculum vulgare Mill. · also called Fennel, sweet fennel, bitter fennel, hinojo (Spanish), fenouil (French), Fenchel (German), finocchio (Italian), funcho (Portuguese), 茴香 hui xiang (Chinese)

Fennel is a tall, feathery plant of the carrot family. Its dried fruit, usually called fennel seed, is a spice and a traditional tea for gas, bloating and colic, and the plant also gives a bulb vegetable and an essential oil. Researchers have studied the seed, tea, oil and extracts, mostly in small trials.

General information, not medical advice. Last substantive update October 25, 2026 · Not medically reviewed. A named clinician has not signed off on this page. How this page is made

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About Fennel

Fennel (Foeniculum vulgare) is a feathery plant of the carrot family. Its seed is a spice and a traditional tea for gas, bloating and infant colic, and it is also made into an oil and capsules. Research is mostly small trials: low certainty for infant colic, irritable bowel syndrome (as a curcumin and fennel oil mix), period pain and bowel recovery after surgery, mixed for menopause and weight, and weaker for everything else. The main safety questions are estragole (EU limits for babies, children, pregnancy and breastfeeding), allergy, and caution with the concentrated oil.

What it is

Fennel (Foeniculum vulgare) is a tall, feathery plant of the carrot family (Apiaceae), related to dill, anise, celery and cumin. A review describes it as generally considered native to the Mediterranean shores and now widespread. The dried fruit, called fennel seed, is the part used as a spice, tea and for oil; the swollen leaf base of a vegetable type (Florence fennel) is eaten as a bulb.

The EU recognises two types: bitter fennel (var. vulgare) and sweet fennel (var. dulce). The difference matters mainly for the amount of estragole in the oil, which is higher in bitter fennel.

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Traditional and current uses

A 2012 review says fennel has long been used in Europe, the Mediterranean and Asia for gas, cramps and as a milk-booster, and that fennel infusion is the classic home remedy given to nursing babies for colic and wind. Today fennel tea is also drunk after meals, and fennel is used in herbal blends for colic, bloating, period pain and menopause.

The EU herbal committee's 2024 monographs list traditional use of fennel fruit tea for mild spasmodic stomach and bowel complaints, bloating and gas, minor spasm with menstrual periods and cough with colds, based only on long-standing use. This is not proof from trials.

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What is in it and how it works

Fennel oil is mostly trans-anethole (about 65 to 78% in two oils analysed), plus fenchone and a smaller amount of estragole. Tea extracts only a small fraction of the estragole; the oil concentrates it.

In the lab, fennel tea relaxed the upper stomach and increased contraction of the lower stomach in guinea pig tissue, and anethole improved delayed stomach emptying in rodents. A breakdown product of anethole bound to the oestrogen receptor in cells. None of this has been shown to explain a benefit in people.

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What the research shows

There are no large, high-quality trials. The best-supported uses are infant colic (two small placebo-controlled trials and a pooled analysis of three fennel-containing trials), IBS (one 30-day trial of a curcumin and fennel oil combination) and period pain (many small trials, mostly from Iran, with very inconsistent pooled results). Several 'positive' trials tested fennel mixed with other herbs, including laxatives such as senna.

Menopause results are mixed, vaginal cream and skin gel trials come from small single groups, and for milk supply Cochrane could not say whether fennel helps. No human trial was found for blood sugar or cough.

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At a glance

Traditional uses history, not proof

European and Mediterranean folk medicine: a 2012 review says fennel was used as a remedy for gas and cramps, as an infusion for babies' colic, as a milk-booster and as an eye lotion.
European herbal medicine: the EU herbal committee lists fennel fruit tea as a traditional medicine for mild cramping stomach complaints including bloating and gas, minor spasm with periods, and cough with colds, based on long use only.
Persian and Chinese traditional medicine: trial authors describe fennel in laxative blends, as an infusion for infrequent periods, and as a heated pack for 'cold' stomach pain.

Studied for research

Infant colic, irritable bowel syndrome and period pain: low certainty
After-surgery bowel recovery and hirsutism with fennel on the skin: low certainty
Menopause symptoms, appetite and weight: mixed
Gas, constipation, PMS, sleep and mood in menopause, vaginal dryness, PCOS, fertility, knee pain: very low
Indigestion, milk supply, blood sugar, cough and anxiety: insufficient evidence

Main compounds

trans-Anethole: the main compound of fennel oil, responsible for the sweet aniseed taste
Estragole: a small part of fennel oil that causes liver tumours in rodents at high doses and is the basis of EU safety limits
Fenchone and 1,8-cineole in the oil, and small amounts of sun-sensitising furocoumarins in the fruit

Common forms

Fennel seed as a spice
Fennel fruit tea (infusion)
Fennel essential oil and oil emulsions
Fennel capsules and extracts, and fennel in herbal blends

Research links: EU herbal monograph on bitter fennel fruit, final revision 2024 (European Medicines Agency) · EU herbal monograph on sweet fennel fruit, final revision 2024 (European Medicines Agency) · LactMed: fennel and breastfeeding (US National Library of Medicine, abstract) · Fennel and infant colic: meta-analysis of breastfed infants (Harb 2016, abstract) · Dietary supplements for period pain: Cochrane review (abstract) · Research Library · Genes & Biomarkers Library

The plant and its history

Accepted scientific name: Foeniculum vulgare Mill.
Naming authority: Mill. (Philip Miller), Gard. Dict., ed. 8: n.° 1 (1768) (GBIF). GBIF status: accepted species (name-match confidence 98). NCBI Taxonomy files fennel under a different name, Anethum foeniculum (taxid 2849586), so the two databases do not use the same name.
Synonyms: Anethum panmorium Roxb. ex Fleming; Anethum pannorium Roxb.; Foeniculum luteum Fisch.; Foeniculum luteum Fisch. ex Sweet; Foeniculum sativum Gaertn.; Meum piperatum Ten.; Meum piperinum Colla; Tenoria romana Schkuhr ex Schult.
Common names: Fennel (English); Sweet fennel (var. dulce) (English); Bitter fennel (var. vulgare) (English); Hinojo (Spanish); Fenouil commun (French); Fenchel (Echter Fenchel) (German); Finocchio comune (Italian); Funcho; erva-doce (Portuguese); Hui xiang (茴香) (Chinese); Shamar (شمر) (Arabic)
Botanical family: Apiaceae (the carrot or parsley family, also called Umbelliferae; order Apiales). Relatives include carrot, celery, dill, anise, caraway, coriander and cumin. Allergy can cross between members of this family, which is why the EU monograph lists hypersensitivity to Apiaceae as a reason not to use fennel.
Classification: Plantae > Tracheophyta > Magnoliopsida (dicots) > Apiales > Apiaceae > Foeniculum > Foeniculum vulgare
Native range: The review by Rafieian and colleagues says fennel is generally considered native to the Mediterranean shores and has become widespread in many regions of the world (abstract of p36803269). GBIF lists it as introduced in places such as the Galapagos and Saint Helena. Native range was not checked against a flora.
Habitat: A hardy perennial herb (Rafieian). Not verified against a flora; habitat details such as soil and climate were not retrieved.
What the plant looks like: Roots: Not described in the sources read.; Stems: Grooved stems (Rafieian abstract). Height and hollow stems not verified.; Leaves: Intermittent leaves with a sheath at the base of the leaf stalk (Rafieian abstract). The finely feathered leaf form is general knowledge, not checked against a flora.; Flowers: Usually bisexual flowers in a yellow umbrella-shaped cluster (an umbel) (Rafieian abstract).; Fruit: The dry fruit, commonly called 'seed', is the part used medicinally (EU monographs 'fructus'). It is the source of the essential oil: about 2 to 6% oil in bitter fennel fruit, with anethole as the main compound (draft EMA statement table and Rafieian).
Cultivation: Not covered by the sources read. Commercial supply details (countries, farming) were not verified.
Harvest and processing: Not verified in detail. The EU monographs describe the herbal substance as dry fruit that complies with the European Pharmacopoeia and used as a herbal tea; oil is distilled from the fruit (EFSA opinion mentions oils from fruit and stems). Oil content, estragole level and solvent differ between products.
Look-alikes and adulterants: Name: Poison hemlock (Conium maculatum); Note: Accepted species, family Apiaceae (GBIF key 3034807). A deadly poisonous relative with similar-looking feathery leaves and umbrella flowers. That it is poisonous and easily confused is general knowledge, not taken from a source read here. Never pick wild plants for eating unless an expert has identified them.; Name: Dill (Anethum graveolens); Note: Accepted species, family Apiaceae (GBIF key 3034646). Similar feathery leaves and umbels; a different herb with a different taste. Dill oil is a known adulterant of fennel oil (Liu 2026).; Name: Anise (Pimpinella anisum); Note: Accepted species, family Apiaceae (GBIF key 8080300). Its fruit also contains anethole and smells similar; anise oil is a known adulterant of fennel oil.; Name: Star anise (Illicium verum); Note: Accepted species, family Schisandraceae, NOT the carrot family (GBIF key 2889756). Its oil also contains anethole and is used to adulterate or imitate fennel oil (Murphy 2024).; Name: Giant fennel (Ferula communis); Note: Accepted species, family Apiaceae (GBIF key 8048981). A different, larger plant; a review of its toxicity exists (PubMed 26949491, not read). Not the same as culinary fennel.; Name: Sea fennel (Crithmum maritimum); Note: Accepted species, family Apiaceae (GBIF key 3632234). A coastal herb sometimes called sea fennel; not a Foeniculum.

The plant and the parts used

A cup of fennel tea beside a pile of fennel seeds (the dried fruit of Foeniculum vulgare) — Fennel seed and a cup of fennel tea.

Fennel seeds and ground fennel on a wooden board — Whole and ground fennel seed, the part used.

Traditional use and history history, not clinical proof

Tradition or era	Documented use	Source
Traditional European, Mediterranean and Asian use (as summarised in a 2012 review)	Gori and colleagues write that fennel was traditionally used in Europe and the Mediterranean as an antispasmodic, diuretic, anti-inflammatory, painkiller, secretion-promoting remedy, milk-booster (galactagogue) and eye lotion; as a poultice for snake bites; in Asian cultures to speed removal of poisons; that it was one of the ancient Saxons' nine sacred herbs; and that in the Middle Ages it was hung over doorways on Midsummer's Eve to ward off spirits. They also call fennel infusion the classical remedy for nursing babies for gas and colic cramps.	p22899959
Persian (Iranian) traditional medicine	Iranian trial authors describe fennel as part of traditional laxative blends (constipation trial, PMID 31763211) and, as an infusion with dry cupping, a traditional Persian treatment for infrequent periods (PMID 30856025). These statements come from trial abstracts, not from historical texts read directly.	p30856025
Traditional Chinese nursing	A Chinese trial describes heated fennel mixed with coarse salt, pressed on the skin, as a traditional nursing treatment for 'cold' stomach pain.	p35951072
EU herbal regulation (2007 and 2024)	The EU herbal committee adopted monographs on bitter fennel fruit and sweet fennel fruit on 5 July 2007 and issued revised versions adopted on 31 January 2024. They recognise traditional use for mild spasmodic stomach and bowel complaints including bloating and gas, minor spasm with menstrual periods, and cough with colds, 'exclusively based upon long-standing use'.	s-ema-hmpc-fennel-bitter
Estragole safety review (2005 onward)	In November 2005 the EU herbal committee adopted a public statement on estragole, concluding that short-term adult use at recommended doses does not pose a significant cancer risk but that exposure of young children, pregnant and breastfeeding women should be minimised. A revision was drafted in 2014 and its limits appear in the 2024 monographs.	s-ema-estragole-statement-2014-draft
Proposed end of the EU monograph on fennel oil (2022)	In July 2022 the committee said that, because of new safety concerns, it could no longer support an EU herbal monograph on bitter fennel oil and proposed withdrawing it.	s-hmpc-meeting-report-2022-07
Modern use for milk supply	LactMed describes fennel as a purported milk-boosting herb used in traditional medicine and in proprietary mixtures.	s-lactmed-fennel

Traditional use shows how a plant was used. It does not show that a supplement works or is safe today.

What is inside, and how it may work

What the plant contains and how those compounds act in cells and animals. Laboratory and animal mechanisms are not proven effects in people.

Main compounds

Compound	Family	Where it is concentrated	Activity studied	Level of evidence
trans-Anethole PubChem 637563	phenylpropanoid (aromatic ether)	Fruit (essential oil) 78.2% of one fennel seed oil analysed by GC-MS (Felix 2026) and 64.6% in another (Stefanescu 2023). Content varies by variety, origin and distillation.	Main compound of fennel oil and the usual 'marker' of its smell and taste. In rodents it improved delayed stomach emptying; in mice it reduced lung inflammation; in cells its breakdown product bound the oestrogen receptor. Described by LactMed as a phytoestrogen that passes into breast milk. Weak mutagenicity in animals (EU monograph). It forms the same DNA and haemoglobin adduct types as estragole, at lower levels. ^{25 100 11 88 62 15 96 92}	Animal research
Estragole (methyl chavicol) PubChem 8815	phenylpropanoid (alkenylbenzene)	Fruit (essential oil) 3.5 to 12% of bitter fennel oil and 1.5 to 5.0% of sweet fennel oil, about 0.3% of bitter fennel fruit (draft EMA statement table); up to 6.1% in bitter oil and 5.0% in sweet oil (EFSA). In dry fennel preparations 0.15 to 13.3 mg/g (van den Berg 2014).	Causes liver tumours in rodents at high doses after being activated by liver enzymes; basis of the EU's limits for children, pregnancy and breastfeeding. A minor oil component but the main safety concern. ^{91 92 99 22 52 21}	Animal research
Fenchone PubChem 14525	monoterpene ketone	Fruit (essential oil) 24.5% of one fennel oil analysed (Stefanescu 2023)	Named as a major oil constituent by LactMed. The sources read gave no activity data for fenchone alone. ^{100 96}	None found
1,8-Cineole (eucalyptol) PubChem 2758	monoterpene ether	Fruit (essential oil) Not given in the sources read	Listed by LactMed among fennel oil constituents. No activity data from the sources read. ⁹⁶	None found
Psoralen PubChem 6199	furocoumarin	Fruit Total furocoumarin intake up to 1.22 micrograms a day at the highest EU monograph amount (Kerekes 2019, three compounds together)	A family of sun-sensitising compounds. Levels in fennel fruit were below the strictest safety recommendations. ⁴³	Laboratory research
Bergapten (5-methoxypsoralen) PubChem 2355	furocoumarin	Fruit See psoralen entry	As above. ⁴³	Laboratory research
Imperatorin PubChem 10212	furocoumarin	Fruit See psoralen entry	As above. ⁴³	Laboratory research

Mechanisms, receptors and pathways

Target or pathway	Gene or receptor	What was found	Level
Stomach smooth muscle (store-operated calcium entry)	Store-operated Ca2+ channels (exact target not identified)	Fennel tea relaxed the upper stomach and increased contraction force in the lower stomach in guinea pig tissue strips. Nerve and nitric oxide blockers did not stop it; the store-operated calcium channel blocker SKF-96365 did. ¹⁰	Animal research
Stomach emptying and accommodation	Not identified	Anethole improved clonidine-induced delayed stomach emptying in mice (not normal emptying) and improved stomach accommodation in rats. Fennel oil gave the same effect. ¹¹	Animal research
Estragole bioactivation (liver enzymes then sulfate conjugation)	Cytochrome P450 enzymes; sulfotransferases (SULT)	After hydroxylation by P450 enzymes and sulfation by SULT, estragole forms 1'-sulfoxyestragole, which makes DNA adducts and causes liver tumours in rodents. In rats, adducts rose with dose and were highest in liver. ^{67 21 15 7}	Animal research
Detoxification and excretion of estragole in people	Glutathione conjugation (mercapturic acid AMPAC)	In 12 volunteers who drank fennel tea, the glutathione-based breakdown product AMPAC appeared in urine within the first hour, with a half-life of about 1.1 hours and near-complete clearance within 8 hours, with large differences between people. ⁵⁷	Human data
Anethole bioactivation	Same pathway as estragole (3'-hydroxyanethole, 3'-sulfoxyanethole)	Anethole formed the same adduct types as estragole in rat and human liver fractions at lower levels. In a pilot, haemoglobin adducts rose in volunteers drinking fennel tea for four weeks and fell after stopping. ¹⁵	Human data
Differences between people in estragole activation	Liver enzyme activity	A computer model based on liver fractions predicted that 0.02% of a dietary dose is converted to the cancer-causing metabolite in Chinese donors versus 0.09% in Caucasian donors. ⁶⁵	Laboratory research
Blocking of the activating enzyme by other plant compounds	SULT inhibition by flavonoids (quercetin, kaempferol, nevadensin and others)	In cells and models, certain flavonoids from herbs and spices, especially nevadensin from basil, strongly reduced estragole DNA adducts. Not shown for fennel itself. ^{8 7}	Laboratory research
Whole fennel versus oil in liver cells	Cell death and DNA damage	In human HepG2 liver cells, fennel seed powder caused no DNA damage or cell death; fennel seed oil caused no DNA damage but strong dose-dependent cell death at the highest dose. ⁴⁸	Laboratory research
Oestrogen receptor	Oestrogen receptor alpha (ESR1)	A breakdown product of anethole (4-hydroxy-1-propenylbenzene), not anethole itself, displaced oestradiol from the receptor and made MCF-7 breast cancer cells grow at low concentrations; at much higher concentrations anethole reduced survival of both oestrogen-sensitive and insensitive breast cancer cells. ^{62 17}	Laboratory research
Steroid hormone production	StAR, CYP11A1, HSD3B1/2, SULT2A1, HSD17B1/4/5, CYP19 (aromatase) promoter via PKA and PKC	In a human fetal adrenal-placenta cell co-culture, estragole and trans-anethole raised oestradiol, oestrone, DHEA, androstenedione, progesterone and oestriol and changed several steroid-making enzymes. ⁸⁶	Laboratory research
Lung inflammation	Th17/Treg balance, IL-17, IL-10, ERK and NF-kB	In mice with bacterial-toxin lung injury, trans-anethole reduced lung damage and shifted immune cells toward regulatory T cells; a fennel extract lowered IL-6, TNF-alpha, MMP-9 and nitric oxide and reduced ERK phosphorylation. ^{88 45}	Animal research
Blood sugar	Not identified	Fennel essential oil lowered blood glucose in diabetic rats with oral and skin use. ¹⁰⁰	Animal research
Metal binding in the gut (drug absorption)	Metal ions in the extract	Fennel extract cut ciprofloxacin absorption in rats; the authors attribute this to metal ions forming a complex with the antibiotic. ⁹⁰	Animal research

Absorption, metabolism and elimination

Absorption: No blood-level study of anethole or fenchone after tea or capsules was found. Fennel's estragole is absorbed after drinking tea: in 12 volunteers its breakdown product appeared in urine within the first hour (p31565931).
Distribution: The EU monographs say there is evidence that trans-anethole is excreted in human breast milk (also LactMed). No tissue distribution data in people were found.
Metabolism: In liver fractions and cells, estragole is hydroxylated by P450 enzymes then sulfated or glucuronidated; the sulfate is reactive and the glucuronide is a detoxification product. Anethole follows the same route more weakly. Glutathione conjugation to AMPAC was shown in people (p31565931, p34015424, p22844077).
Elimination: AMPAC half-life 0.78 to 1.54 hours (mean 1.13 +/- 0.21), nearly cleared in 8 hours; total excreted 93 to 1,076 nanograms after 500 mL of tea containing 2.2 mg estragole, showing large between-person differences (p31565931).
Bioavailability: Not measured for any fennel compound in people. In rats, an aqueous fennel extract cut ciprofloxacin bioavailability to about 0.52 of control (p10678493).

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Isolated compounds versus whole extracts

Fennel tea, powdered seed and essential oil are very different exposures. The oil concentrates anethole and estragole; tea extracts only a small fraction of estragole (infusions held 0.4 to 133.4 micrograms per 25 mL from 1 g of fruit, and whole fruit gives about three times less than cut fruit). Whole fennel contains other compounds that may change how estragole is handled: in a human liver cell test, fennel seed powder did not damage DNA while the oil killed cells at the highest dose, and other herbs' flavonoids can block estragole activation (not shown for fennel). The EU monograph limits are set on daily estragole intake; the Gori review argues the matrix lowers the risk, a view the EU documents read here do not adopt. Trials of 'fennel' therefore cannot be compared across products, and animal tests with pure estragole or anethole overstate or understate what tea does.

Nutritional composition

USDA FoodData Central, 'Fennel, bulb, raw' (SR Legacy, FDC ID 169385, NDB 11957, published 2019-04-01), per 100 g raw bulb: energy 31 kcal (129 kJ), protein 1.24 g, fat 0.2 g, carbohydrate 7.3 g, fibre 3.1 g, calcium 49 mg, iron 0.73 mg, magnesium 17 mg, potassium 414 mg, manganese 0.191 mg, vitamin C 12 mg, folate 27 micrograms. This is the vegetable bulb (Florence fennel type); fennel fruit (seed) used as a spice or tea was not retrieved because the USDA API rate limit was reached, so no seed nutrient figures are given.

21benefits and uses looked at

100studies and sources checked

Low certaintybest evidence rating found

18lab markers tracked in trials

2 mixed findings5 low certainty8 very low certainty6 not enough evidence

What was looked at

The 21 benefits and uses checked for Fennel, each with how strong the evidence is. Tap one to open it.

Infant colic: crying and fussing in the first monthsLow certainty
Irritable bowel syndrome (IBS): pain, bloating and bowel habitLow certainty
Indigestion and upper-stomach discomfort (functional dyspepsia)Not enough evidence
Gas and bloating (flatulence) after surgery or in daily lifeVery low certainty
ConstipationVery low certainty
Getting the bowels moving after abdominal surgeryLow certainty
Chronic upper-stomach pain treated with a heated fennel and salt pack plus moxibustionNot enough evidence
Period pain (primary dysmenorrhoea)Low certainty
Premenstrual syndrome (PMS)Very low certainty
Menopause symptoms such as hot flushesMixed findings
Sleep and mood in menopauseVery low certainty
Vaginal dryness and sexual function after menopauseVery low certainty
Breast milk supply (galactagogue use)Not enough evidence
Polycystic ovary syndrome (PCOS) and irregular periodsVery low certainty
Unwanted facial hair (hirsutism), as a cream or gel on the skinLow certainty
Fertility measures (ovarian reserve, womb lining)Very low certainty
Knee osteoarthritis painVery low certainty
Appetite, weight and blood fatsMixed findings
Anxiety and well-being with fennel oil massageNot enough evidence
Blood sugarNot enough evidence
Cough and chest congestionNot enough evidence

Lab markers tracked in the studies

Crying time in colicky infants (minutes per day)Share of infants whose colic resolved (crying under 9 hours a week)IBS symptom severity score (IBS-SSS)Colonic transit time (hours)Time to first passing of gas after surgery (hours)Gas (flatulence) score on a visual scalePeriod pain score (visual scale)PMS symptom scoreMenopause symptom score (Menopause Rating Scale or Kupperman index)Blood oestradiolSleep quality score (Pittsburgh Sleep Quality Index)Cholesterol and triglyceridesVaginal cell maturation and pHFacial hair diameter or thicknessAntral follicle count and AMHWomb lining (endometrial) thicknessWOMAC knee pain and function scoreMilk volume and infant weight

What is Fennel good for?

The main proposed uses and how strong the human evidence is for each. "Moderate" means good trials point the same way; "low" and "very low" mean small or inconsistent trials; "mixed" means results disagree; "insufficient" means too little to judge.

Benefits, one by one

Each card is a research question, not a promise. Tap a goal to filter. Open a card to see the studies, doses and limits.

Infant colic: crying and fussing in the first months

Low certainty

A few small trials suggest fennel oil (and a fennel-chamomile-lemon balm extract) may cut crying time in colicky babies. Reviews call this promising but low in confidence, because the trials are small, some use mixed herbs, and one product dominates. Safety in babies is a separate and important question (see the safety tab): the EU herbal committee does not recommend fennel preparations for children under 4.

7 studiesFennel seed oil emulsion (Alexandrovich), a standardised chamomile-fe…

Studies, doses and limits

What the trials found

Alexandrovich 2003 (125 infants aged 2 to 12 weeks, Russia): fennel seed oil emulsion versus placebo; colic was judged gone in 65% (40/62) on fennel versus 23.7% (14/59) on placebo. Savino 2005 (93 breastfed infants, Italy): a three-herb extract (chamomile, fennel, lemon balm; ColiMil) cut daily crying from about 201 to 77 minutes versus about 199 to 170 on placebo over one week. A meta-analysis of three fennel-containing trials (Harb 2016) found 72 minutes a day less crying (95% CI -126 to -18). Reviews (Perry 2011, Perry 2019, Anheyer 2017) call fennel extract promising but note flaws, missing independent repeats and high or unclear risk of bias. A 2023 parent survey of 1,218 families (Gavish) found 65% of parents rated a fennel-based product as successful, but there was no placebo and the authors were consultants to the maker.

Results

Small to moderate reductions in crying time in the trials, with large uncertainty. None of the trials looked at long-term safety.

Effect sizes as reported

Fennel oil emulsion: colic gone in 65% versus 23.7% (absolute risk reduction 41%, 95% CI 25 to 57). Meta-analysis of 3 fennel-containing trials: -72.1 min/day (95% CI -126.4 to -17.7).

Why this rating

Positive results come from a small number of small trials, one of them a three-herb combination, and the reviewers rate most reviews and trials as high or unclear risk of bias with no independent repeat of the main trial. The 3-trial pooled range is very wide.

Form and dose studied

Fennel seed oil emulsion (Alexandrovich), a standardised chamomile-fennel-lemon balm extract (Savino), and fennel-based commercial products (Gavish). Different products cannot be swapped for one another.

Who was studied

Colicky infants roughly 2 weeks to 3 months old, mostly breastfed.

Limits

Few trials; different products; two of the three trials in the pooled result are not fennel alone; crying time is reported by parents; colic usually improves with age on its own; funding often not stated.

Why researchers looked

Colic (long spells of crying in an otherwise healthy baby, usually in the first three months) is very common and hard on parents. Fennel tea has been given to babies for generations, so researchers tested it.

Traditional use

Gori and colleagues note that fennel infusions are the classic home remedy given to nursing babies for gas and colic cramps. Fennel is also a traditional European remedy for mild cramping stomach complaints in older children and adults.

Proposed mechanism Preliminary mechanism

Fennel oil and its main compound, trans-anethole, relaxed stomach muscle in guinea pig tissue and helped delayed stomach emptying in rodents. No study has shown that this is how fennel works in a colicky baby.

A proposed mechanism does not show that the effect happens in people.

No side effects were reported in these trials, but they were short. The EU monographs do not recommend fennel fruit preparations under 4 years because of lack of data and the estragole question. See the safety file.

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Irritable bowel syndrome (IBS): pain, bloating and bowel habit

Low certainty

One placebo-controlled trial found that a capsule combining curcumin (from turmeric) and fennel essential oil eased IBS symptoms over 30 days, and an open study using a turmeric-plus-fennel-oil product reported improvement over two months. Fennel was never tested alone, so we cannot say how much of the effect is fennel.

3 studiesCurcumin plus fennel essential oil capsules (a combination). Not fenn…

Studies, doses and limits

What the trials found

Portincasa 2016 (121 adults with mild to moderate IBS, Italy): curcumin plus fennel essential oil capsules or placebo for 30 days. The average IBS symptom score fell 50% with the capsules versus 26% with placebo (P<0.001); 25.9% were symptom-free versus 6.8% (P=0.005). Di Ciaula 2018 (211 adults, open, no control group): a turmeric-plus-fennel-oil product (Enterofytol) was followed by lower symptom scores and better quality of life over two months, in all IBS subtypes. A 2020 meta-analysis of Western herbal medicines in IBS (Hawrelak, 33 trials) found peppermint oil, Aloe vera and asafoetida effective; the curcumin-fennel oil combination showed efficacy in one trial that had not been repeated.

Results

Better symptom scores than placebo in one 30-day trial of a combination product; an uncontrolled study agrees in direction.

Effect sizes as reported

IBS symptom score relative fall 50.05 +/- 28.85% versus 26.12 +/- 30.62% with placebo (P<0.001); symptom-free 25.9% versus 6.8%.

Why this rating

Only one placebo-controlled trial, 30 days long, of a curcumin plus fennel oil combination; the second study had no control group. The meta-analysis notes the result has not been repeated.

Form and dose studied

Curcumin plus fennel essential oil capsules (a combination). Not fennel tea, seed or oil alone.

Who was studied

Adults with mild to moderate IBS (all subtypes in the open study).

Limits

Fennel was not tested alone. Short duration. Funding not stated in the abstracts. Placebo group improved about a quarter.

Why researchers looked

IBS is common, has few good treatments, and fennel is a traditional antispasmodic and anti-gas herb.

Traditional use

The EU herbal committee lists bitter and sweet fennel fruit tea as a traditional medicine for mild, cramping stomach and bowel complaints including bloating and gas. This is a statement about long use, not proof from trials.

Proposed mechanism Pharmacological theory

Fennel oil is thought to relax gut muscle and curcumin to calm inflammation. The trial authors proposed this; it was not measured in the trial.

A proposed mechanism does not show that the effect happens in people.

No serious problems reported in these studies. Essential oil is concentrated, and the EU herbal committee proposed in 2022 to withdraw its monograph on bitter fennel oil because of new safety concerns (see safety file).

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Indigestion and upper-stomach discomfort (functional dyspepsia)

Not enough evidence

There is no trial of fennel on its own for indigestion. The only human study found used a seven-ingredient supplement, was not randomised, and cannot show what fennel did. Lab and animal work suggests a plausible way fennel could help, but that is not proof it helps people.

3 studiesMulti-ingredient supplement (human); fennel tea strips and anethole (…

Studies, doses and limits

What the trials found

Pellicano 2014 (91 adults with functional dyspepsia after H. pylori treatment): an open, non-randomised comparison of a supplement of alginate, calcium carbonate, pineapple, papaya, ginger, an enzyme and fennel. All 55 users and 31 of 36 non-users stayed off acid-reducing drugs while waiting for a breath test (P=0.008); well-being improved by 1.78 points with the supplement. No randomised trial of fennel alone for dyspepsia was found.

Results

Cannot say anything about fennel itself.

Effect sizes as reported

Not available for fennel alone.

Why this rating

No controlled trial of fennel alone; the one human study is open, non-randomised and a seven-ingredient combination.

Form and dose studied

Multi-ingredient supplement (human); fennel tea strips and anethole (animal tissue).

Who was studied

Adults with functional dyspepsia (human); guinea pig stomach and mice/rats (lab).

Limits

No fennel-only human data. Open-label design. Lab work does not guarantee an effect in people.

Why researchers looked

Fennel is a classic after-meal herb used for fullness, bloating and indigestion.

Traditional use

Used for centuries in Europe and Asia after heavy meals (the EU monograph recognises traditional use for mild spasmodic stomach complaints including bloating).

Proposed mechanism Animal research

In guinea pig stomach strips, fennel tea relaxed the upper stomach and made the lower stomach contract more strongly (Annahazi 2025). In mice and rats, anethole, the main compound of fennel oil, improved drug-delayed stomach emptying and helped the stomach relax to hold food (Asano 2016).

A proposed mechanism does not show that the effect happens in people.

No adverse effects were reported in the open study.

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Gas and bloating (flatulence) after surgery or in daily life

Very low certainty

One small hospital trial in women after caesarean section found that fennel capsules eased gas about as well as dimethicone, a standard anti-gas medicine. There was no placebo group, so we do not know how much was due to fennel. No trial in everyday bloating was found.

1 studiesFennel capsules (dose not stated in the abstract).

Studies, doses and limits

What the trials found

Jourshari 2024 (double-blind trial of women after a caesarean section in Iran): fennel capsules versus dimethicone capsules, one dose every 6 hours for four doses. Gas scores fell in both groups and did not differ between them after adjusting for baseline (P=0.607).

Results

Both treatments reduced gas; fennel did no better or worse than dimethicone.

Effect sizes as reported

No between-group difference (F(1,72)=0.27, P=0.607).

Why this rating

One small trial with no placebo, in a special situation (just after surgery), with fennel dose not given in the abstract.

Form and dose studied

Fennel capsules (dose not stated in the abstract).

Who was studied

Women after caesarean section.

Limits

No placebo; gas often settles on its own; one centre; abstract only.

Why researchers looked

Gas after surgery is common and uncomfortable. Fennel is a traditional carminative (a remedy for gas).

Traditional use

The EU monograph lists fennel fruit tea for bloating and gas on the basis of long traditional use.

Proposed mechanism Pharmacological theory

The trial authors suggest fennel stimulates bowel movement. Not tested in the trial.

A proposed mechanism does not show that the effect happens in people.

No harm was reported in the abstract (not specifically stated).

⁴¹

Constipation

Very low certainty

Several small trials of herbal formulas that contain fennel found better bowel movements than placebo or even than a standard laxative. But every formula contained other herbs, and three contained senna or aloe, which are well-known laxatives. Fennel alone has not been tested for constipation.

4 studiesHerbal formulas and teas (fruit/seed with other herbs). No fennel-alo…

Studies, doses and limits

What the trials found

Azimi 2022 (50 adults over 60 with functional constipation, Iran): a fennel-plus-Damask-rose formula improved constipation severity, stool consistency and quality of life more than polyethylene glycol 4000 (all P<0.001) with milder side effects. Eliasvandi 2019 (64 postmenopausal women): a ten-ingredient capsule that includes anise or fennel and senna leaves gave more bowel movements than placebo (mean difference 4.2). Picon 2010 (20 adults, crossover): a tea of anise, fennel, elderberry and senna cut colon transit time from 42.3 to 15.7 hours (P<0.001). Ghafarzadegan 2025 (61 patients after fracture surgery): a capsule of senna, aloe, fennel, coriander and caraway improved constipation (P<0.001).

Results

Formulas containing fennel work better than placebo in short trials, but the active ingredient is likely senna or aloe in three of them. The fennel-plus-rose formula had no stimulant laxative and beat a standard laxative on some measures.

Effect sizes as reported

Transit time 15.7 h (95% CI 11.1 to 20.2) versus 42.3 h (33.5 to 51.1) on placebo (Picon, with senna). Bowel movement frequency +4.2 versus placebo (Eliasvandi, with senna).

Why this rating

All trials are small, short, tested mixtures, and three contained senna or aloe. Fennel's own contribution is unknown. Only one used a fennel-plus-rose mix with no stimulant laxative, in 50 older adults.

Form and dose studied

Herbal formulas and teas (fruit/seed with other herbs). No fennel-alone product tested.

Who was studied

Older adults, postmenopausal women, adults with chronic constipation, orthopaedic patients after surgery (opioid-related).

Limits

Combination products; senna/aloe confounders; very small samples; short follow-up; abstract-only reading; one confidence interval is printed inconsistently in the original abstract.

Why researchers looked

Fennel is part of many traditional laxative blends in Persian, Brazilian and other herbal traditions.

Traditional use

Traditional Persian medicine books list fennel in laxative blends; the trial authors describe this. This is traditional use, not proof.

Proposed mechanism Pharmacological theory

Not shown. The trial authors suggest fennel helps gut movement; senna and aloe in some blends act on the bowel directly.

A proposed mechanism does not show that the effect happens in people.

Mild diarrhoea in the fennel-rose group; a small fall in blood potassium during the senna-containing tea (Picon). No serious events reported.

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Getting the bowels moving after abdominal surgery

Low certainty

Two Chinese randomised trials found that fennel helped bowel function return sooner after major abdominal surgery. One gave fennel fruit tea after gynaecological cancer surgery. The other used a heated fennel pack on the belly (not swallowed). Both are single-centre trials in surgical patients, so they do not tell us about healthy people.

2 studiesFennel fruit tea (filtrate only) in one trial; a heated fennel pack o…

Studies, doses and limits

What the trials found

Ma 2015 (159 women after surgery for gynaecological cancer; article in Chinese): fennel fruit tea (5 g of fruit per cup, filtrate only) twice a day from the first morning after surgery until first flatus versus plain water. Time to first flatus 53.1 versus 64.2 hours, first bowel movement 4.3 versus 5.4 days, hospital stay 5.6 versus 6.7 days (all P<0.001); ileus symptoms were more common with water (relative risk 2.6, 95% CI 1.5 to 4.5). Chen 2020 (381 patients after major abdominal surgery for liver, pancreas or stomach tumours): a heated fennel pack on the belly versus a heated rice-husk pack. Time to first flatus, first bowel movement and fasting time were shorter (P<0.05 each), bloating eased (P<0.001); in patients with bowel reconstruction hospital stay was 9.25 versus 11.1 days (P=0.023).

Results

Faster return of bowel function and shorter hospital stay in both trials.

Effect sizes as reported

Tea: flatus 53.1 versus 64.2 h; stay 5.6 versus 6.7 days; ileus RR 2.6 (1.5 to 4.5). Pack: hospital stay in reconstruction subgroup 9.25 versus 11.1 days (P=0.023).

Why this rating

Two randomised trials of reasonable size agree in direction, but both are single-centre, in Chinese surgical patients, and one is not blinded (tea versus water). The pack trial's fennel is applied to skin.

Form and dose studied

Fennel fruit tea (filtrate only) in one trial; a heated fennel pack on the abdomen in the other.

Who was studied

Adults after major abdominal or gynaecological cancer surgery in China.

Limits

Single centre; tea trial compares with water; the pack trial tests external heat with a heated control pack; hospital-stay result was a subgroup; abstracts only.

Why researchers looked

After abdominal surgery the bowel often slows down (ileus), which delays eating and going home. Cheap, safe aids are wanted.

Traditional use

Warm fennel packs and fennel tea are used in traditional Chinese nursing for stomach and belly problems.

Proposed mechanism Pharmacological theory

Not tested in these trials. The authors suggest fennel stimulates gut movement; heat itself may also help.

A proposed mechanism does not show that the effect happens in people.

The tea authors call it safe and well tolerated (no specific adverse events listed in the abstract). Surgical patients should only use anything by mouth if their surgical team agrees.

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Chronic upper-stomach pain treated with a heated fennel and salt pack plus moxibustion

Not enough evidence

One Chinese trial of 96 people found that a heated fennel-and-salt pack on the skin plus moxibustion eased stomach pain more than routine care. Because two treatments were combined and applied outside the body, it says little about fennel itself.

1 studiesExternal fennel-salt hot pack plus moxibustion.

Studies, doses and limits

What the trials found

Zhang 2022 (96 patients with chronic upper stomach pain of the 'spleen-stomach vacuity cold' pattern, equal to chronic atrophic gastritis): fennel mixed with coarse salt, heated and pressed on the skin, together with moxibustion at the navel, versus routine care. The treated group had greater falls in stomach pain, better quality of life and higher satisfaction (P<0.05).

Results

Better symptom score than routine care; cannot separate fennel from moxibustion and heat.

Effect sizes as reported

Not given as numbers in the abstract.

Why this rating

Two treatments given together against routine care only; external use; abstract does not give numbers.

Form and dose studied

External fennel-salt hot pack plus moxibustion.

Who was studied

Hospital patients in Guangxi, China.

Limits

Fennel effect cannot be isolated; no sham; abstract only.

Why researchers looked

Traditional Chinese nursing uses warming treatments for the 'cold' pattern of stomach pain.

Traditional use

Warm fennel and salt packs are a traditional Chinese nursing treatment.

Proposed mechanism Pharmacological theory

Not tested.

A proposed mechanism does not show that the effect happens in people.

Skin burns are possible with any hot pack (general caution, not reported in the study).

⁸⁹

Period pain (primary dysmenorrhoea)

Low certainty

Fennel is the best-studied of fennel's women's-health uses: more than a dozen small trials, mostly from Iran and mostly in students, suggest it can ease period pain, and several found it about as good as mefenamic acid or ibuprofen. Cochrane, however, rates the evidence for all supplements in this area as low or very low, and the trials disagree with each other a lot.

9 studiesFennel capsules, extract, oil/essence and tea; details differ between…

Studies, doses and limits

What the trials found

Lee 2020 (meta-analysis, 12 randomised trials): seven trials (n=502) found fennel similar to conventional drugs for pain (SMD 0.07, 95% CI -0.08 to 0.21); against placebo (n=468) fennel was better (SMD -3.27, 95% CI -5.28 to -1.26) but the trials disagreed very strongly (I2 98%), with signs of publication bias. Shahrahmani 2021 (12 studies): fennel beat placebo (SMD -0.632, 95% CI -0.827 to -0.436, 7 articles) and did not differ from mefenamic acid (SMD -0.214, 95% CI -0.446 to 0.017). Xu 2020 gave a small fennel effect (WMD 0.528, very wide CI 0.119 to 6.829). Thaliyil Poduval 2026 (14 trials of carrot-family herbs) found carrot-family herbs including fennel were effective add-ons, with some bias concerns. The Cochrane review (Pattanittum 2016, 27 trials of supplements) rated all evidence low or very low quality; for fennel versus placebo one trial of 43 women found no consistent benefit (MD -0.34 points, 95% CI -0.74 to 0.06). Individual trials: Namavar Jahromi 2003 (30 women): fennel essence and mefenamic acid both beat no treatment; mefenamic acid was stronger on days 2 and 3 and 5 women dropped out because of the smell. Modaress Nejad 2006 (110 girls): 80% versus 73% had relief on fennel versus mefenamic acid, not significantly different. Ghodsi 2014 (80 students, no-treatment control): lower nausea and weakness and shorter periods. Negi 2026 (384 women, crossover): fennel lowered pain (to 4.61 from about 6) versus placebo (6.24), but ginger worked better.

Results

Many small positive trials; the best pooled analyses disagree on how much, and Cochrane judges the evidence low or very low.

Effect sizes as reported

Versus placebo: SMD -0.632 (95% CI -0.827 to -0.436) in one meta-analysis; SMD -3.27 with I2 98% in another; Cochrane MD -0.34 points (95% CI -0.74 to 0.06, one trial). Versus mefenamic acid: no clear difference (SMD 0.07 and -0.214).

Why this rating

Many small trials point the same way, but the main pooled analyses differ widely, risk of bias is moderate with signs of publication bias, Cochrane rates all supplement evidence low or very low, and most data come from students in one country.

Form and dose studied

Fennel capsules, extract, oil/essence and tea; details differ between trials.

Who was studied

Young women and students, mostly in Iran, with moderate to severe period pain.

Limits

Small trials; mixed products; high inconsistency; no long-term data; side effects poorly reported (only three of twelve trials checked); odour was a reason to drop out.

Why researchers looked

Period cramps are very common in young women, and drugs like ibuprofen do not suit everyone. Fennel is a traditional remedy for menstrual cramps.

Traditional use

The EU herbal committee lists bitter and sweet fennel fruit tea as a traditional medicine for minor spasm associated with menstrual periods. That is long-standing use, not trial proof. The EU monograph does not recommend this use under age 12.

Proposed mechanism Pharmacological theory

Fennel tea relaxed stomach muscle in guinea pig tissue, and the trial authors suggest fennel may relax the womb in a similar way. Relaxing the womb was not shown in the women studied.

A proposed mechanism does not show that the effect happens in people.

One trial reported a mild rise in menstrual flow; another PMS combination trial reported more bleeding. Women who are pregnant, or hormone-sensitive, should read the safety file.

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Premenstrual syndrome (PMS)

Very low certainty

Three small Iranian trials suggest fennel (alone or with another herb) may lower PMS symptom scores, but all are small and short. One branded fennel extract and one fennel plus Persian borage mix were tested; one trial found more bleeding with its fennel mix.

3 studiesBranded fennel extract; fennel plus Echium flower; fennel extract (de…

Studies, doses and limits

What the trials found

Shayan 2026 (90 students): a branded fennel extract (30 mg) cut PMS severity by 79.3% versus no significant change with placebo (P=0.016) over two cycles; no side effects reported. Motevalli Haghi 2024 (80 women): fennel 1 g/day plus Echium amoenum flower 2 g/day beat placebo on daily symptom subscales and quality of life; bleeding volume rose in the herb group at two months. Delaram 2011 (90 students, single-blind): fennel extract lowered PMS scores to 64.4 versus 79.1 with placebo (P<0.001).

Results

All three trials favoured fennel over placebo, but trials are small and short.

Effect sizes as reported

PMS severity -79.3% with fennel extract (P=0.016, versus no change for placebo); score 64.4 versus 79.1 (P<0.001).

Why this rating

Three small trials, short (two cycles), two with unclear blinding or combinations, no independent replication.

Form and dose studied

Branded fennel extract; fennel plus Echium flower; fennel extract (details not in the abstracts).

Who was studied

Female students and young women, Iran.

Limits

Small; short; combinations; PMS symptoms are self-rated and respond strongly to placebo; abstract only.

Why researchers looked

PMS affects many women; fennel is a traditional women's remedy.

Traditional use

No specific traditional claim for PMS appears in the abstracts read. The EU monograph lists traditional use of fennel fruit tea for minor spasm associated with menstrual periods.

Proposed mechanism Pharmacological theory

Authors suggest fennel's plant-oestrogen-like compounds or effect on serotonin. Not tested in these trials.

A proposed mechanism does not show that the effect happens in people.

One combination trial reported a rise in bleeding volume.

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Menopause symptoms such as hot flushes

Mixed findings

Results are mixed. A 2021 meta-analysis of two placebo-controlled trials found fennel eased menopausal symptoms, and two further trials agreed, but one placebo-controlled trial found no difference because its placebo group improved too. All were small and from Iran.

8 studiesFennel soft capsules (100 mg x 2 daily), fennel seed powder 2 g daily…

Studies, doses and limits

What the trials found

Lee 2021 (meta-analysis, 7 randomised trials): two placebo-controlled trials (n=145) favoured fennel for menopausal symptoms (SMD -1.32, 95% CI -1.76 to -0.87), but risk of bias was concerning and other outcomes were unclear. Rahimikian 2017 (90 women, triple-blind): menopause rating scale fell with fennel at 4, 8 and 10 weeks versus placebo (P<0.001). Ghaffari 2020 (80 women): symptom score fell from 30.8 to 19 with fennel seed powder (2 g) versus 31.2 to 26.4 with starch; oestradiol did not differ. Mahdavian 2019 (120 women): a chamomile-fennel-saffron mix improved menopause scores in the two higher-dose groups. Jenabi 2023 (76 women): a fennel-valerian extract lowered hot flash frequency and severity versus placebo. Ghazanfarpour 2018 (50 women, double-blind): both groups improved, with no significant difference from placebo; the authors blame a high placebo response. Ghavi 2023 (125 women): FSH and oestradiol changed with fennel and evening primrose oil versus placebo, but the direction is not given in the abstract.

Results

Two to four small trials favour fennel; one equally small trial does not. Hormone-level findings are inconsistent.

Effect sizes as reported

Meta-analysis of 2 trials: SMD -1.32 (95% CI -1.76 to -0.87). Kupperman index -11.8 points with fennel versus -4.8 with starch (Ghaffari, own subtraction).

Why this rating

Small trials disagree: some show clear benefit, one shows none with a high placebo response, and the meta-analysis pooled only two trials with concerning risk of bias.

Form and dose studied

Fennel soft capsules (100 mg x 2 daily), fennel seed powder 2 g daily, mixed extracts. Products differ.

Who was studied

Postmenopausal and perimenopausal women aged 45 to 65, Iran.

Limits

Small; short; combinations; placebo response high in menopause trials; oestrogen effect unresolved; abstract only.

Why researchers looked

Fennel contains anethole, which has weak oestrogen-like effects in lab tests, so researchers asked whether it could help menopausal symptoms.

Traditional use

No specific traditional claim for menopause appears in the abstracts read.

Proposed mechanism Laboratory research

In lab cells, a breakdown product of anethole bound to the oestrogen receptor and made breast cancer cells grow (Nakagawa 2003), but one trial found blood oestradiol did not rise with fennel (Ghaffari 2020). So whether fennel eases menopause symptoms through an oestrogen-like effect is unproven.

A proposed mechanism does not show that the effect happens in people.

No serious side effects reported in the trials. Women with hormone-sensitive cancers should talk to their doctor first because of fennel's weak plant-oestrogen-like compounds (see safety).

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Sleep and mood in menopause

Very low certainty

Oral fennel alone did not improve sleep quality or depression and anxiety scores in menopausal women in two small trials. A fennel plus valerian mix improved sleep scores versus placebo, but valerian is itself a sleep herb.

3 studiesFennel capsules; fennel-valerian extract capsules.

Studies, doses and limits

What the trials found

Afiat 2018 (50 women): no significant difference in the Pittsburgh Sleep Quality Index (total P=0.439); a non-significant tendency for sleep duration (P=0.059). Ghazanfarpour 2018 (60 women): no significant overall fall in anxiety or depression scores; a borderline or significant improvement in the women who had anxiety or depression to begin with (subgroup). Jenabi 2023 (76 women): fennel-valerian extract lowered PSQI versus placebo at 2 months (P=0.030).

Results

Fennel alone: no clear benefit. Fennel plus valerian: better sleep score.

Effect sizes as reported

PSQI total P=0.439 (fennel alone); fennel-valerian PSQI P=0.030 versus control.

Why this rating

Two small null trials of fennel alone, one positive combination trial in which valerian could explain the effect, and one subgroup finding.

Form and dose studied

Fennel capsules; fennel-valerian extract capsules.

Who was studied

Menopausal women, Iran.

Limits

Small; subgroup analysis; combination with valerian; self-rated sleep.

Why researchers looked

Poor sleep and low mood are common in menopause.

Traditional use

No specific traditional claim found.

Proposed mechanism Animal research

Animal studies suggest fennel compounds may act on mood pathways (cited by the trial authors). Not shown in people.

A proposed mechanism does not show that the effect happens in people.

No side effects reported in the sleep trial.

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Vaginal dryness and sexual function after menopause

Very low certainty

Fennel taken by mouth did not help vaginal atrophy in one trial. A fennel cream put in the vagina did in two small trials from the same group, but those are single small studies and the effects look unusually large.

3 studiesOral fennel capsules (no effect); 5% fennel vaginal cream (effect rep…

Studies, doses and limits

What the trials found

Ghazanfarpour 2017 (60 women, oral fennel for 3 months): no significant difference from placebo in vaginal cell counts (superficial cells P=0.82). Yaralizadeh 2016 (60 women, 5% fennel vaginal cream daily for 8 weeks): superficial cells 76.1 versus 11.8 on placebo (P<0.001); vaginal pH improved in all women on fennel versus 7.4% on placebo. Abedi 2018 (60 women, same cream): total sexual function score 33.79 versus 18.99 on placebo (P<0.001).

Results

Oral: no benefit. Vaginal cream: big improvements reported in two small trials from one research group.

Effect sizes as reported

Cream: superficial cells 76.1 +/- 15.3 versus 11.8 +/- 8; FSFI 33.79 versus 18.99.

Why this rating

The positive results come from two small trials of a vaginal cream by one group, with unusually large effects; the oral trial was null.

Form and dose studied

Oral fennel capsules (no effect); 5% fennel vaginal cream (effect reported).

Who was studied

Postmenopausal women, Iran.

Limits

Small (60 each); same group; no independent replication; surrogate cell counts; abstract only.

Why researchers looked

Fennel's weak plant-oestrogen-like compounds might act on the vaginal lining, as oestrogen cream does.

Proposed mechanism Pharmacological theory

A possible weak oestrogen-like effect at the vaginal lining. Not measured directly.

A proposed mechanism does not show that the effect happens in people.

The cream trials reported no side effects, but a fennel cream's absorption and effect on the womb lining were not checked.

^{31 87 1}

Breast milk supply (galactagogue use)

Not enough evidence

Fennel is widely used by breastfeeding mothers to boost milk supply, but good evidence is lacking. The Cochrane review says it is very uncertain whether fennel (or fenugreek) helps infant weight, and results for milk volume could not be combined. A safety trial of a fennel-containing tea found no harm in mothers or babies over a month.

3 studiesFennel tea, fennel in blended 'lactation' teas and capsules.

Studies, doses and limits

What the trials found

Foong 2020 (Cochrane review, 41 trials, 3,005 mothers, of drug and natural galactagogues): evidence overall was low to very low certainty; 'very uncertain whether fennel or fenugreek improves infant weight'; milk volume results for natural products could not be pooled (I2 99%); reported side effects were minor. LactMed reports that two small studies saw increases in some measures (milk volume, fat content, infant weight gain) with fennel, while no rise in prolactin was found. Wagner 2019 (60 mothers with no milk shortage): Mother's Milk tea (bitter fennel, anise, coriander, fenugreek and other herbs) versus lemon verbena tea for 30 days found no adverse effects in mothers or infants up to 12 months and no differences in infant growth. This trial tested safety, not supply.

Results

No reliable evidence that fennel raises milk supply; short-term safety of one blended tea looked reassuring in a small trial.

Effect sizes as reported

Not pooled for fennel (Cochrane).

Why this rating

Cochrane rates the whole field low to very low and cannot say whether fennel improves infant weight; the one safety trial did not test supply.

Form and dose studied

Fennel tea, fennel in blended 'lactation' teas and capsules.

Who was studied

Breastfeeding mothers of healthy term infants.

Limits

Blends; mothers without milk shortage; no fennel-only trials in the abstracts; large inconsistency; abstract only.

Why researchers looked

Many mothers worry about low milk supply, and fennel is a classic folk 'milk-boosting' herb.

Traditional use

LactMed describes fennel as a purported galactagogue used in traditional medicine and in proprietary milk-supply products.

Proposed mechanism Pharmacological theory

LactMed notes that anethole is a plant oestrogen-like compound but that no rise in prolactin was found with fennel in nursing mothers.

A proposed mechanism does not show that the effect happens in people.

LactMed and the EU monographs urge caution: anethole passes into breast milk, and large intakes caused toxicity in two newborns; the EU monograph says pregnancy and breastfeeding use is not recommended. See safety.

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Polycystic ovary syndrome (PCOS) and irregular periods

Very low certainty

Small trials have used fennel in PCOS with mixed results: one fennel plus cupping combination shortened the time between periods compared with metformin, ovarian follicle counts were lower in a three-month trial, but fennel did not add to weight loss on a diet. Nothing here is strong enough to guide care.

3 studiesFennel infusion plus cupping; fennel capsules or extract.

Studies, doses and limits

What the trials found

Mokaberinejad 2019 (61 women with PCOS and infrequent periods): fennel infusion plus dry cupping for 6 months gave shorter gaps between periods than metformin (about 31 versus 41 to 43 days). Ghavi 2023 (47 women): fennel (46 mg twice daily) and Ferula both lowered follicle counts versus placebo (P<0.05); only Ferula changed DHEAS and TSH. Nadjarzadeh 2021 (64 women): fennel added to a low-calorie diet did not significantly improve weight or androgens.

Results

Mixed and mostly small; no consistent benefit on hormones or weight.

Effect sizes as reported

Cycle length about 31 versus 41-43 days (fennel plus cupping versus metformin).

Why this rating

Three small trials with different designs (a combination with cupping versus metformin, a three-arm trial of 47 women, a factorial diet trial); no replication.

Form and dose studied

Fennel infusion plus cupping; fennel capsules or extract.

Who was studied

Women with PCOS, Iran.

Limits

Small; no placebo in the largest positive result; two treatments combined; abstract has a typing error in one figure.

Why researchers looked

PCOS involves irregular periods and raised male hormones, and fennel is used in traditional Persian medicine for infrequent periods.

Traditional use

Persian traditional medicine uses fennel infusion with dry cupping for infrequent periods (as described by the trial authors).

Proposed mechanism Pharmacological theory

Possible plant-oestrogen-like effects. Not shown in these trials.

A proposed mechanism does not show that the effect happens in people.

No serious adverse events reported in the abstracts.

^{56 30 61}

Unwanted facial hair (hirsutism), as a cream or gel on the skin

Low certainty

Two small double-blind trials found that fennel extract cream or gel on the skin made facial hair thinner. The creams were put on skin, so the results do not apply to tea or capsules.

2 studiesTopical fennel extract cream (1 to 2%) or gel (3%).

Studies, doses and limits

What the trials found

Javidnia 2003 (38 women with idiopathic hirsutism): 1% and 2% fennel extract creams versus placebo; hair diameter fell 7.8%, 18.3% and -0.5% respectively. Akha 2014 (44 women, 24 weeks): 3% fennel gel cut hair thickness from 97.9 to 75.6 microns; itching or irritation was reported by a few patients and was not statistically different from placebo.

Results

Thinner hair with fennel cream or gel in two small trials.

Effect sizes as reported

Hair diameter -18.3% with 2% cream versus +0.5% placebo; thickness -22.3 microns with 3% gel (within-group).

Why this rating

Two small double-blind trials agree, but they are small, of unclear duration, and the second reports only the within-group change.

Form and dose studied

Topical fennel extract cream (1 to 2%) or gel (3%).

Who was studied

Women with idiopathic hirsutism, Iran.

Limits

Small; skin-only; no replication; cosmetic outcome.

Why researchers looked

Fennel was thought to have oestrogen-like effects that might lower the male-hormone effect on hair.

Traditional use

Not found.

Proposed mechanism Pharmacological theory

Authors suggest an oestrogen-like effect on hair follicles. Not shown.

A proposed mechanism does not show that the effect happens in people.

Itching or irritation reported by some users (not significantly different from placebo). Fennel on skin plus sun can cause skin reactions; see safety.

^{39 4}

Fertility measures (ovarian reserve, womb lining)

Very low certainty

Two small Iranian trials looked at ultrasound measures in infertile women. Fennel raised antral follicle count slightly in one and womb-lining thickness during clomiphene treatment in another. Neither showed more babies, and one found no change in the main hormone (AMH).

2 studiesFennel extract capsules.

Studies, doses and limits

What the trials found

Banaei 2025 (60 infertile women with occult premature ovarian insufficiency, 60 days): AMH unchanged (P=0.986); antral follicle count 1.6 higher with fennel (95% CI 0.07 to 3.1; P=0.040). Kamali 2025 (60 women on clomiphene): endometrium 1.7 mm thicker with fennel (60 mg/day) than control (P<0.001); pregnancy 16% versus 3% (not significant).

Results

Small changes in scan measures; no proof of better fertility.

Effect sizes as reported

Antral follicle count +1.6 (0.07 to 3.1); endometrial thickness +1.7 mm.

Why this rating

Two small trials, ultrasound surrogates only, one without placebo, no pregnancy benefit shown.

Form and dose studied

Fennel extract capsules.

Who was studied

Infertile women, Iran.

Limits

Surrogate outcomes; no live birth data; small.

Why researchers looked

The trial authors cite fennel's antioxidant properties and possible benefits on ovarian function.

Traditional use

Not found.

Proposed mechanism Pharmacological theory

Authors cite antioxidant properties; not tested.

A proposed mechanism does not show that the effect happens in people.

Women trying to conceive should not use fennel supplements without medical advice because safety in pregnancy is not established (EU monograph).

^{14 42}

Knee osteoarthritis pain

Very low certainty

One small two-week trial in 66 women found fennel seed extract capsules reduced knee pain and disability more than placebo. It is the only trial.

1 studiesSweet fennel seed extract capsules.

Studies, doses and limits

What the trials found

Alazadeh 2020 (66 women, double-blind): sweet fennel seed extract capsules for 2 weeks lowered WOMAC pain, disability and total score and visual pain score more than placebo; stiffness did not differ between groups.

Results

Less pain than placebo after two weeks.

Effect sizes as reported

Numbers not given in the abstract.

Why this rating

One short, small trial, first of its kind, abstract gives no numbers.

Form and dose studied

Sweet fennel seed extract capsules.

Who was studied

Women with knee osteoarthritis, Iran.

Limits

Two weeks only; one trial; abstract only.

Why researchers looked

Fennel extracts showed anti-inflammatory effects in the lab.

Traditional use

Not found.

Proposed mechanism Animal research

Anti-inflammatory activity in animals and cells (not measured in the trial).

A proposed mechanism does not show that the effect happens in people.

No safety data in the abstract.

⁵

Appetite, weight and blood fats

Mixed findings

Evidence is thin and conflicting. Fennel tea eased hunger ratings in nine women for one meal, a chia plus fennel seed trial reported better weight and cholesterol (without numbers), but fennel alone did not change cholesterol or body weight in postmenopausal women.

4 studiesFennel tea, fennel with chia seeds, fennel capsules.

Studies, doses and limits

What the trials found

Bae 2015 (9 overweight women, crossover): fennel tea lowered hunger and raised fullness ratings versus placebo tea (P<0.05) but did not change food eaten at lunch. Khan 2024 (obese adults, 3 months): chia plus fennel seeds reported better BMI and lipids (P<0.05); no numbers in the abstract. Afiat 2018 (60 postmenopausal women, 3 months): no significant effect on cholesterol, LDL, HDL or triglycerides. Saghafi 2017 (47 overweight postmenopausal women): no significant effect on weight, BMI, waist or fat distribution.

Results

Mixed: tiny positive appetite and combination results, null results for fennel alone on weight and lipids.

Effect sizes as reported

Lipids: triglycerides P=0.679, total cholesterol P=0.103, LDL P=0.146, HDL P=0.266 (fennel versus placebo).

Why this rating

Positive appetite and combination-seed findings conflict with null results for fennel alone on weight and lipids; all studies are small.

Form and dose studied

Fennel tea, fennel with chia seeds, fennel capsules.

Who was studied

Overweight women, obese adults, postmenopausal women.

Limits

Tiny crossover (9 people); no numbers in the chia trial; combination; short.

Why researchers looked

Fennel seeds are fibre-rich and traditional as digestive and appetite herbs.

Traditional use

Not found.

Proposed mechanism Pharmacological theory

Not shown; fibre content proposed by the chia-fennel authors.

A proposed mechanism does not show that the effect happens in people.

No adverse effects reported.

^{13 44 3 78}

Anxiety and well-being with fennel oil massage

Not enough evidence

A small exploratory Portuguese-authored trial found massage with fennel oil lowered anxiety scores more than massage with almond oil alone after two months. Sleep and well-being were not statistically different. Evidence is preliminary.

1 studies1.6% fennel essential oil in sweet almond oil, used as massage.

Studies, doses and limits

What the trials found

Felix 2026 (40 participants, 2 months, massage every 15 days): state anxiety was 32.47 with fennel oil massage versus 41.75 with plain massage after the last session (difference -9.28, P=0.007); changes over time within each group were not significant, and sleep and well-being differences were not significant.

Results

Lower anxiety after the last session, but not clearly a change over time.

Effect sizes as reported

State anxiety difference -9.28.

Why this rating

One exploratory study of 40 people with an odd pattern (no significant change over time within groups).

Form and dose studied

1.6% fennel essential oil in sweet almond oil, used as massage.

Who was studied

Adults (details limited).

Limits

Exploratory; small; skin and smell exposure only.

Why researchers looked

Fennel oil has been suggested to reduce anxiety and aid sleep.

Traditional use

Not found.

Proposed mechanism Preliminary mechanism

Not tested; trans-anethole made up 78.2% of the oil used.

A proposed mechanism does not show that the effect happens in people.

Fennel essential oil is a skin and respiratory sensitiser (EFSA animal-feed opinion). See safety.

²⁵

Blood sugar

Not enough evidence

No human trial was found. A rat study reported lower blood sugar after fennel essential oil. That is not evidence for people.

1 studiesEssential oil (rats).

Studies, doses and limits

What the trials found

No randomised human trial of fennel for blood sugar was found in PubMed searches. A diabetic rat study (Stefanescu 2023, essential oil with 64.6% trans-anethole and 24.5% fenchone, 4 weeks) found significantly lower blood sugar with both skin and oral use.

Results

Animal only.

Effect sizes as reported

Not available for humans.

Why this rating

Rat data only.

Form and dose studied

Essential oil (rats).

Who was studied

Diabetic rats.

Limits

No human data.

Why researchers looked

Fennel is a folk remedy for diabetes in several countries.

Traditional use

Not found in the sources read.

Proposed mechanism Animal research

Not clear.

A proposed mechanism does not show that the effect happens in people.

People on diabetes medicines should not assume fennel is safe to combine; no interaction studies exist.

¹⁰⁰

Cough and chest congestion

Not enough evidence

Fennel fruit tea is a traditional EU-listed expectorant for cough with colds. We found no human trial. Mouse studies show anti-inflammatory effects in injured lungs, which does not show it helps coughs.

3 studiesFennel fruit tea (traditional); extract or anethole in mice.

Studies, doses and limits

What the trials found

No human trials of fennel for cough were found. Evidence is the EU monograph's traditional-use listing and two mouse studies (Zhang 2018, Lee 2015).

Results

No human results.

Effect sizes as reported

Not available.

Why this rating

Traditional use and mouse studies only.

Form and dose studied

Fennel fruit tea (traditional); extract or anethole in mice.

Who was studied

Mice.

Limits

No human trials.

Why researchers looked

Fennel is a traditional cough remedy.

Traditional use

The EU herbal monographs (2024) list traditional use of fennel fruit tea as an expectorant for cough associated with colds, based on long-standing use only.

Proposed mechanism Animal research

In mice with lung injury caused by a bacterial toxin, a fennel extract and trans-anethole lowered inflammation. Both were given as injections or at high doses.

A proposed mechanism does not show that the effect happens in people.

EU limits on estragole apply to teas; see safety file.

^{92 88 45}

Connections to the rest of health

How Fennel connects to the rest of our health knowledge graph. Every link says what kind of connection it is. A safety link (for example to the liver) is a warning, not a benefit. A study that merely mentions a topic never creates a benefit link.

Explore every connection: goals, body systems, organs, symptoms, genes

Kind of connection Connected to Search

A. Wellness goals

Connected to	Kind of connection	Evidence status	Context	Studies
Women's wellness	Potential benefit	Low certainty	Period pain: many small trials, low certainty; menopause mixed. Preparation or compound: Fennel fruit capsules, extract	^{46 80 68 47}
Digestive Support	Potential benefit	Low certainty	Infant colic: crying and fussing in the first months: A few small trials suggest fennel oil (and a fennel-chamomile-lemon balm extract) may cut crying time in colicky babies. Reviews call this promising but low in confidence, because the trials are small, some use mixed herbs, and one product dominates. Safety in babies is a separate and important question (see the safety tab): the EU herbal committee does not recommend fennel preparations for children under 4. Irritable bowel syndrome (IBS): pain, bloating and bowel habit: One placebo-controlled trial found that a capsule combining curcumin (from turmeric) and fennel essential oil eased IBS symptoms over 30 days, and an open study using a turmeric-plus-fennel-oil product reported improvement over two months. Fennel was never tested alone, so we cannot say how much of the effect is fennel.	^{6 79 37 70 71 9 26 73 20 38 12 23 72 27 50 18}
Calm Relaxation	Potential benefit	Low certainty	Infant colic: crying and fussing in the first months: A few small trials suggest fennel oil (and a fennel-chamomile-lemon balm extract) may cut crying time in colicky babies. Reviews call this promising but low in confidence, because the trials are small, some use mixed herbs, and one product dominates. Safety in babies is a separate and important question (see the safety tab): the EU herbal committee does not recommend fennel preparations for children under 4. Anxiety and well-being with fennel oil massage: A small exploratory Portuguese-authored trial found massage with fennel oil lowered anxiety scores more than massage with almond oil alone after two months. Sleep and well-being were not statistically different. Evidence is preliminary.	^{6 79 37 70 71 9 26 25}
Gut Health	Potential benefit	Low certainty	Irritable bowel syndrome (IBS): pain, bloating and bowel habit: One placebo-controlled trial found that a capsule combining curcumin (from turmeric) and fennel essential oil eased IBS symptoms over 30 days, and an open study using a turmeric-plus-fennel-oil product reported improvement over two months. Fennel was never tested alone, so we cannot say how much of the effect is fennel. Constipation: Several small trials of herbal formulas that contain fennel found better bowel movements than placebo or even than a standard laxative. But every formula contained other herbs, and three contained senna or aloe, which are well-known laxatives. Fennel alone has not been tested for constipation.	^{73 20 38 12 23 72 27 50 18}
Digestive Support	Traditional use	Not enough evidence	Indigestion and upper-stomach discomfort (functional dyspepsia): There is no trial of fennel on its own for indigestion. The only human study found used a seven-ingredient supplement, was not randomised, and cannot show what fennel did. Lab and animal work suggests a plausible way fennel could help, but that is not proof it helps people. Gas and bloating (flatulence) after surgery or in daily life: One small hospital trial in women after caesarean section found that fennel capsules eased gas about as well as dimethicone, a standard anti-gas medicine. There was no placebo group, so we do not know how much was due to fennel. No trial in everyday bloating was found.	^{69 10 11 41 89}
Gut Health	Traditional use	Not enough evidence	Indigestion and upper-stomach discomfort (functional dyspepsia): There is no trial of fennel on its own for indigestion. The only human study found used a seven-ingredient supplement, was not randomised, and cannot show what fennel did. Lab and animal work suggests a plausible way fennel could help, but that is not proof it helps people.	^{69 10 11}
Womens Wellness	Potential benefit	Low certainty	Period pain (primary dysmenorrhoea): Fennel is the best-studied of fennel's women's-health uses: more than a dozen small trials, mostly from Iran and mostly in students, suggest it can ease period pain, and several found it about as good as mefenamic acid or ibuprofen. Cochrane, however, rates the evidence for all supplements in this area as low or very low, and the trials disagree with each other a lot. Premenstrual syndrome (PMS): Three small Iranian trials suggest fennel (alone or with another herb) may lower PMS symptom scores, but all are small and short. One branded fennel extract and one fennel plus Persian borage mix were tested; one trial found more bleeding with its fennel mix.	^{46 80 85 83 68 63 54 34 64 81 58 19 47 77 28 32 51 40 29 62 31 87 1 56 30 61 39 4 14 42}
Hormone Balance	Potential benefit	Low certainty	Period pain (primary dysmenorrhoea): Fennel is the best-studied of fennel's women's-health uses: more than a dozen small trials, mostly from Iran and mostly in students, suggest it can ease period pain, and several found it about as good as mefenamic acid or ibuprofen. Cochrane, however, rates the evidence for all supplements in this area as low or very low, and the trials disagree with each other a lot. Premenstrual syndrome (PMS): Three small Iranian trials suggest fennel (alone or with another herb) may lower PMS symptom scores, but all are small and short. One branded fennel extract and one fennel plus Persian borage mix were tested; one trial found more bleeding with its fennel mix.	^{46 80 85 83 68 63 54 34 64 81 58 19 56 30 61}
Mood Balance	Potential benefit	Very low certainty	Premenstrual syndrome (PMS): Three small Iranian trials suggest fennel (alone or with another herb) may lower PMS symptom scores, but all are small and short. One branded fennel extract and one fennel plus Persian borage mix were tested; one trial found more bleeding with its fennel mix. Sleep and mood in menopause: Oral fennel alone did not improve sleep quality or depression and anxiety scores in menopausal women in two small trials. A fennel plus valerian mix improved sleep scores versus placebo, but valerian is itself a sleep herb.	^{81 58 19 2 33 40}
Menopause Support	Potential benefit	Mixed findings	Menopause symptoms such as hot flushes: Results are mixed. A 2021 meta-analysis of two placebo-controlled trials found fennel eased menopausal symptoms, and two further trials agreed, but one placebo-controlled trial found no difference because its placebo group improved too. All were small and from Iran. Sleep and mood in menopause: Oral fennel alone did not improve sleep quality or depression and anxiety scores in menopausal women in two small trials. A fennel plus valerian mix improved sleep scores versus placebo, but valerian is itself a sleep herb.	^{47 77 28 32 51 40 29 62 2 33 31 87 1}
Better Sleep	Potential benefit	Very low certainty	Sleep and mood in menopause: Oral fennel alone did not improve sleep quality or depression and anxiety scores in menopausal women in two small trials. A fennel plus valerian mix improved sleep scores versus placebo, but valerian is itself a sleep herb.	^{2 33 40}
Womens Wellness	Traditional use	Not enough evidence	Breast milk supply (galactagogue use): Fennel is widely used by breastfeeding mothers to boost milk supply, but good evidence is lacking. The Cochrane review says it is very uncertain whether fennel (or fenugreek) helps infant weight, and results for milk volume could not be combined. A safety trial of a fennel-containing tea found no harm in mothers or babies over a month.	^{24 84 96}
Hair Support	Potential benefit	Low certainty	Unwanted facial hair (hirsutism), as a cream or gel on the skin: Two small double-blind trials found that fennel extract cream or gel on the skin made facial hair thinner. The creams were put on skin, so the results do not apply to tea or capsules.	^{39 4}
Fertility Support	Potential benefit	Very low certainty	Fertility measures (ovarian reserve, womb lining): Two small Iranian trials looked at ultrasound measures in infertile women. Fennel raised antral follicle count slightly in one and womb-lining thickness during clomiphene treatment in another. Neither showed more babies, and one found no change in the main hormone (AMH).	^{14 42}
Joint Support	Potential benefit	Very low certainty	Knee osteoarthritis pain: One small two-week trial in 66 women found fennel seed extract capsules reduced knee pain and disability more than placebo. It is the only trial.	⁵
Inflammation Balance	Potential benefit	Very low certainty	Knee osteoarthritis pain: One small two-week trial in 66 women found fennel seed extract capsules reduced knee pain and disability more than placebo. It is the only trial.	⁵
Weight Management	Potential benefit	Mixed findings	Appetite, weight and blood fats: Evidence is thin and conflicting. Fennel tea eased hunger ratings in nine women for one meal, a chia plus fennel seed trial reported better weight and cholesterol (without numbers), but fennel alone did not change cholesterol or body weight in postmenopausal women.	^{13 44 3 78}
Cholesterol Balance	Potential benefit	Mixed findings	Appetite, weight and blood fats: Evidence is thin and conflicting. Fennel tea eased hunger ratings in nine women for one meal, a chia plus fennel seed trial reported better weight and cholesterol (without numbers), but fennel alone did not change cholesterol or body weight in postmenopausal women.	^{13 44 3 78}
Metabolic Health	Potential benefit	Mixed findings	Appetite, weight and blood fats: Evidence is thin and conflicting. Fennel tea eased hunger ratings in nine women for one meal, a chia plus fennel seed trial reported better weight and cholesterol (without numbers), but fennel alone did not change cholesterol or body weight in postmenopausal women.	^{13 44 3 78}
Anxiety Support	Potential benefit	Not enough evidence	Anxiety and well-being with fennel oil massage: A small exploratory Portuguese-authored trial found massage with fennel oil lowered anxiety scores more than massage with almond oil alone after two months. Sleep and well-being were not statistically different. Evidence is preliminary.	²⁵
Blood Sugar Balance	Preliminary mechanism	Not enough evidence	Blood sugar: No human trial was found. A rat study reported lower blood sugar after fennel essential oil. That is not evidence for people.	¹⁰⁰
Metabolic Health	Preliminary mechanism	Not enough evidence	Blood sugar: No human trial was found. A rat study reported lower blood sugar after fennel essential oil. That is not evidence for people.	¹⁰⁰
Immune Support	Traditional use	Not enough evidence	Cough and chest congestion: Fennel fruit tea is a traditional EU-listed expectorant for cough with colds. We found no human trial. Mouse studies show anti-inflammatory effects in injured lungs, which does not show it helps coughs.	^{92 88 45}
Inflammation Balance	Traditional use	Not enough evidence	Cough and chest congestion: Fennel fruit tea is a traditional EU-listed expectorant for cough with colds. We found no human trial. Mouse studies show anti-inflammatory effects in injured lungs, which does not show it helps coughs.	^{92 88 45}

B. Body systems

Connected to	Kind of connection	Evidence status	Context	Studies
Reproductive system	Drug or supplement interaction	Mixed findings	Bleeding in women on DMPA (73% versus 19% placebo); weak oestrogen-like lab activity; pregnancy and breastfeeding use not recommended. Preparation or compound: Fennel fruit; anethole	^{55 62 92}
Liver	Adverse effect or risk	Very low certainty	Rodent liver tumours at high doses; no human case series found. Preparation or compound: Estragole	^{91 16 21}
Immune system (allergy)	Contraindication	Low certainty	Cross-reactivity with the carrot family and mugwort pollen; oil is a skin and airway sensitiser. Preparation or compound: Fennel fruit and oil	^{92 93 22}
Nervous system	Adverse effect or risk	Very low certainty	One seizure case after a large amount of oil. Preparation or compound: Fennel essential oil	⁸²
Skin	Adverse effect or risk	Low certainty	Itching or irritation in gel trial; photosensitivity listed by LactMed; low furocoumarin content in fruit. Preparation or compound: Fennel on the skin, essential oil	^{4 96 43}
Digestive system	Potential benefit	Low certainty	Infant colic, IBS (with curcumin) and post-surgery bowel recovery: small trials, low certainty. Preparation or compound: Fennel oil, tea, extracts	^{6 37 73 50}
Digestive System	Biological association	Low certainty	Studied for: Infant colic: crying and fussing in the first months Studied for: Irritable bowel syndrome (IBS): pain, bloating and bowel habit	^{6 79 37 70 71 9 26 73 20 38 69 10 11 41 12 23 72 27 50 18 89}
Reproductive System	Biological association	Low certainty	Studied for: Period pain (primary dysmenorrhoea) Studied for: Premenstrual syndrome (PMS)	^{46 80 85 83 68 63 54 34 64 81 58 19 47 77 28 32 51 40 29 62 2 33 31 87 1 24 84 96 56 30 61 14 42}
Endocrine System	Biological association	Mixed findings	Studied for: Menopause symptoms such as hot flushes Studied for: Polycystic ovary syndrome (PCOS) and irregular periods	^{47 77 28 32 51 40 29 62 56 30 61 100}
Nervous System	Biological association	Very low certainty	Studied for: Sleep and mood in menopause Studied for: Anxiety and well-being with fennel oil massage	^{2 33 40 25}
Integumentary System	Biological association	Low certainty	Studied for: Unwanted facial hair (hirsutism), as a cream or gel on the skin	^{39 4}
Musculoskeletal System	Biological association	Very low certainty	Studied for: Knee osteoarthritis pain	⁵
Metabolism Weight	Biological association	Mixed findings	Studied for: Appetite, weight and blood fats Studied for: Blood sugar	^{13 44 3 78 100}
Respiratory System	Biological association	Not enough evidence	Studied for: Cough and chest congestion	^{92 88 45}

C. Body parts and organs

Connected to	Kind of connection	Evidence status	Context	Studies
Liver	Adverse effect or risk	Not enough evidence	DNA damage and tumours in rodent liver; weak direct genotoxicity in cells. Preparation or compound: Estragole	^{52 21 67}

G. Root causes and contributing factors

Connected to	Kind of connection	Evidence status	Context	Studies
Medication interactions	Drug or supplement interaction	Very low certainty	Rat study: ciprofloxacin peak level down 83% and exposure down 48% with fennel extract; no human study. Preparation or compound: Aqueous fennel extract	⁹⁰

I. Biomarkers

Connected to	Kind of connection	Evidence status	Context	Studies
Crying time in colicky infants (minutes per day)	Biological association	Low certainty	Measured in trials: lowered. A lab change is not the same as a health benefit.	^{79 37}
Share of infants whose colic resolved (crying under 9 hours a week)	Biological association	Low certainty	Measured in trials: raised. A lab change is not the same as a health benefit.	⁶
IBS symptom severity score (IBS-SSS)	Biological association	Low certainty	Measured in trials: lowered. A lab change is not the same as a health benefit.	^{73 20}
Colonic transit time (hours)	Biological association	Very low certainty	Measured in trials: lowered. A lab change is not the same as a health benefit.	⁷²
Time to first passing of gas after surgery (hours)	Biological association	Low certainty	Measured in trials: lowered. A lab change is not the same as a health benefit.	^{50 18}
Gas (flatulence) score on a visual scale	Biological association	Very low certainty	Measured in trials: lowered. A lab change is not the same as a health benefit.	⁴¹
Period pain score (visual scale)	Biological association	Low certainty	Measured in trials: lowered. A lab change is not the same as a health benefit.	^{46 80 68 64}
PMS symptom score	Biological association	Very low certainty	Measured in trials: lowered. A lab change is not the same as a health benefit.	^{81 19}
Menopause symptom score (Menopause Rating Scale or Kupperman index)	Biological association	Mixed findings	Measured in trials: mixed. A lab change is not the same as a health benefit.	^{47 77 28 32}
Blood oestradiol	Biological association	Mixed findings	Measured in trials: mixed. A lab change is not the same as a health benefit.	^{28 29}
Sleep quality score (Pittsburgh Sleep Quality Index)	Biological association	Very low certainty	Measured in trials: no-change. A lab change is not the same as a health benefit.	^{2 40}
Cholesterol and triglycerides	Biological association	Low certainty	Measured in trials: no-change. A lab change is not the same as a health benefit.	^{3 44}
Vaginal cell maturation and pH	Biological association	Very low certainty	Measured in trials: mixed. A lab change is not the same as a health benefit.	^{31 87}
Facial hair diameter or thickness	Biological association	Low certainty	Measured in trials: lowered. A lab change is not the same as a health benefit.	^{39 4}
Antral follicle count and AMH	Biological association	Very low certainty	Measured in trials: mixed. A lab change is not the same as a health benefit.	^{14 30}
Womb lining (endometrial) thickness	Biological association	Very low certainty	Measured in trials: raised. A lab change is not the same as a health benefit.	⁴²
WOMAC knee pain and function score	Biological association	Very low certainty	Measured in trials: lowered. A lab change is not the same as a health benefit.	⁵
Milk volume and infant weight	Biological association	Not enough evidence	Measured in trials: mixed. A lab change is not the same as a health benefit.	^{24 84}

J. Genes, receptors and enzymes

Connected to	Kind of connection	Evidence status	Context	Studies
Cytochrome P450 enzymes (estragole 1'-hydroxylation)	Preliminary mechanism	In vitro	Activate estragole to its reactive form in liver fractions; individual differences in enzyme activity explain the wide range in urinary AMPAC between volunteers.	^{67 57 65}
Sulfotransferases (SULT)	Preliminary mechanism	In vitro	Make the reactive 1'-sulfoxyestragole; blocked by certain plant flavonoids in cells and models (not shown for fennel).	^{8 7 15}
Oestrogen receptor alpha (ESR1)	Preliminary mechanism	In vitro	A breakdown product of anethole displaced oestradiol from the receptor in a test system and made MCF-7 cells grow at low concentration.	⁶²
CYP19A1 (aromatase) promoter	Preliminary mechanism	In vitro	Estragole and trans-anethole stimulated promoter-specific CYP19 expression through PKA and PKC pathways in fetal adrenal-like and placenta-like cells.	⁸⁶
StAR, CYP11A1, HSD3B1, HSD3B2, SULT2A1, HSD17B1, HSD17B4, HSD17B5	Preliminary mechanism	In vitro	Steroid-making genes whose expression changed with estragole or trans-anethole in the cell co-culture.	⁸⁶

K. Biological pathways

Connected to	Kind of connection	Evidence status	Context	Studies
Store-operated calcium entry in smooth muscle	Preliminary mechanism	Animal	The fennel tea relaxation of upper-stomach muscle was blocked by a store-operated calcium entry blocker.	¹⁰
NF-kB and apoptosis (p53, caspase 9, PARP)	Preliminary mechanism	In vitro	Anethole suppressed cell survival and activated cell-death markers in breast cancer cell lines regardless of oestrogen receptor status, at about 1 millimolar.	¹⁷
ERK / NF-kB inflammatory signalling	Preliminary mechanism	Animal	A fennel extract reduced ERK phosphorylation and inflammatory mediators in mouse lungs.	⁴⁵
IL-17 and IL-10 (Th17/Treg balance)	Preliminary mechanism	Animal	trans-Anethole lowered IL-17 and raised IL-10 and regulatory T cells in mice with lung injury.	⁸⁸

L. Active compounds

Connected to	Kind of connection	Evidence status	Context	Studies
trans-Anethole	Biological association	Animal	Main compound of fennel oil and the usual 'marker' of its smell and taste. In rodents it improved delayed stomach emptying; in mice it reduced lung inflammation; in cells its breakdown product bound the oestrogen receptor. Described by LactMed as a phytoestrogen that passes into breast milk. Weak mutagenicity in animals (EU monograph). It forms the same DNA and haemoglobin adduct types as estragole, at lower levels. Preparation or compound: Fruit (essential oil)	^{25 100 11 88 62 15 96 92}
Estragole (methyl chavicol)	Biological association	Animal	Causes liver tumours in rodents at high doses after being activated by liver enzymes; basis of the EU's limits for children, pregnancy and breastfeeding. A minor oil component but the main safety concern. Preparation or compound: Fruit (essential oil)	^{91 92 99 22 52 21}
Fenchone	Biological association	None found	Named as a major oil constituent by LactMed. The sources read gave no activity data for fenchone alone. Preparation or compound: Fruit (essential oil)	^{100 96}
1,8-Cineole (eucalyptol)	Biological association	None found	Listed by LactMed among fennel oil constituents. No activity data from the sources read. Preparation or compound: Fruit (essential oil)	⁹⁶
Psoralen	Biological association	In vitro	A family of sun-sensitising compounds. Levels in fennel fruit were below the strictest safety recommendations. Preparation or compound: Fruit	⁴³
Bergapten (5-methoxypsoralen)	Biological association	In vitro	As above. Preparation or compound: Fruit	⁴³
Imperatorin	Biological association	In vitro	As above. Preparation or compound: Fruit	⁴³

Each connection is stored with the ingredient, the connected record, the kind of connection, the evidence status, the supporting studies, the preparation or compound involved, and a review date (last reviewed October 25, 2026).

Evidence at a glance: what changed in 18 lab markers

Tap a number to show only those markers. Counts are markers, not people.

Hormonal1 Other9224

The evidence

The research centre for Fennel. Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.

Evidence by outcome

Bars show how many studies we found for each outcome, not how well it works. People are added up across trials only (reviews are not added, to avoid double counting).

How we rate evidence

High certainty

Several well-run trials or reviews agree; further research is unlikely to change the picture much.

Moderate certainty

Good trials point the same way, but some doubt remains.

Low certainty

Small, short or inconsistent trials. The finding could change with better research.

Very low certainty

Very little or very weak human data. Treat as a possibility only.

Mixed findings

Trials or reviews disagree with each other.

Not enough evidence

Not enough human research to say either way.

Evidence against

Good research found no benefit, or found harm.

We take the reviewers' own risk-of-bias and GRADE statements where they exist, and otherwise judge from study size, design, consistency, directness and whether a product matches what is sold. Many publications do not make evidence high. Method note: We searched PubMed, read the abstracts of the studies cited, read the EU herbal monographs on bitter and sweet fennel fruit, the 2022 HMPC meeting report, the 2014 draft EU public statement on estragole and the US LactMed entry on fennel in full, and checked the plant name, chemical IDs and food data against GBIF, NCBI, PubChem and USDA FoodData Central. One retracted paper was skipped.

Study library: every study we checked 100

Design Research type Plant part Year from Search

Study	Design	People	Product, dose, length	Result
Abedi 2018 Effect of fennel vaginal cream on sexual function in postmenopausal women: A double blind randomized controlled trial. J Med Life · PMID 29696061	Randomized controlled trial (double blind)	60 Postmenopausal women with sexual dysfunction	Fennel vaginal cream fruit/seed (cream) 5 g every night 8 weeks · vs Placebo cream	All areas improved in both groups but more with fennel. Total FSFI: 8.2 to 33.79 with fennel versus 8.03 to 18.99 with placebo (P<0.001). FSFI 33.79 vs 18.99 after treatment Methods, limits and funding Outcomes: Female Sexual Function Index (FSFI) Limitations: Applied vaginally; baseline FSFI values are unusually low; from the same research group as the 2016 cream trial; small. Abstract only. Read: abstract
Afiat 2018 Effect of Foeniculum Vulgare (Fennel) on Sleep Quality of Menopausal Women: A Double-blinded, Randomized Placebo-controlled Trial. J Menopausal Med · PMID 30671414 · DOI	Randomized controlled trial (double blind, placebo controlled)	50 Menopausal women, Iran	Fennel soft capsules fruit/seed Not given in the abstract 12 weeks · vs Placebo	No significant difference in total PSQI or its parts. A borderline tendency for sleep duration (P=0.059). No side effects reported. Total PSQI P=0.439 Methods, limits and funding Outcomes: Pittsburgh Sleep Quality Index (PSQI) Limitations: Small; short; subjective measure. Abstract only. Funding and conflicts: The fennel capsules were supplied by Barij Essence Pharmaceutical Company; the authors state the company did not shape design, analysis or conduct Read: abstract
Afiat 2018 The Effect of Short-term Treatment with Fennel on Lipid Profile in Postmenopausal Women: A Randomized Controlled Trial. J Menopausal Med · PMID 29765924 · DOI	Randomized controlled trial (double blind, placebo controlled)	60 Postmenopausal women, Iran	Fennel fruit/seed Not given in the abstract 3 months · vs Placebo	No significant differences between fennel and placebo for any lipid. A borderline HDL rise within the fennel group (P=0.052). Triglycerides P=0.679, total cholesterol P=0.103, LDL P=0.146, HDL P=0.266 Methods, limits and funding Outcomes: Total and LDL cholesterol, HDL cholesterol, triglycerides Limitations: Small; authors suggest higher doses or longer treatment could matter. Abstract only. Funding and conflicts: Authors declared no conflict of interest Read: abstract
Akha 2014 The effect of fennel (Foeniculum vulgare) gel 3% in decreasing hair thickness in idiopathic mild to moderate hirsutism, A randomized placebo controlled clinical trial. Caspian J Intern Med · PMID 24490010	Randomized controlled trial (double blind, placebo controlled)	44 Women with mild to moderate idiopathic hirsutism, Sari, Iran	Fennel gel 3% fruit/seed (gel) Not given in the abstract 24 weeks · vs Placebo gel	Hair thickness fell from 97.9 to 75.6 microns with fennel (P<0.001). Eight patients reported itching (4) or irritation with itching (4); three of each four were on fennel gel. The difference was not statistically significant. Hair thickness -22.3 microns (own subtraction) Methods, limits and funding Outcomes: Facial hair thickness (microscope) Limitations: Small; the abstract shows the change within the fennel group, not the between-group difference. Topical use. Abstract only. Registration: IRCT 138901213672N1 Read: abstract
Alazadeh 2020 Effect of sweet fennel seed extract capsule on knee pain in women with knee osteoarthritis. Complement Ther Clin Pract · PMID 32835919 · DOI	Randomized controlled trial (double blind, placebo controlled)	66 Women with knee osteoarthritis, Iran	Sweet fennel seed extract capsules (200 mg extract from 7 g of seed each) fruit/seed (extract) 4 capsules twice a day 2 weeks · vs Placebo	Pain, disability and total WOMAC score fell more with fennel than placebo (significant difference); stiffness did not differ between groups. Both groups improved. Percentage change larger with fennel (numbers not given in the abstract) Methods, limits and funding Outcomes: WOMAC pain, stiffness, disability and visual pain scale Limitations: Two weeks only; small; abstract gives no numbers; first trial of its kind. Read: abstract
Alexandrovich 2003 The effect of fennel (Foeniculum Vulgare) seed oil emulsion in infantile colic: a randomized, placebo-controlled study. Altern Ther Health Med · PMID 12868253	Randomized controlled trial	125 Infants aged 2 to 12 weeks with colic (Wessel criteria), two clinics in Russia (St Petersburg)	Fennel seed oil emulsion fruit/seed (oil) Not given in the abstract Not given in the abstract (cumulative crying judged against a weekly threshold) · vs Placebo	Colic was eliminated in 65% (40/62) of infants on fennel oil emulsion and 23.7% (14/59) on placebo (P<0.01). No side effects reported in either group. Absolute risk reduction 41%; number needed to treat 2 (ARR 95% CI 25 to 57; NNT 95% CI 2 to 4) Methods, limits and funding Outcomes: Colic relief, defined as cumulative crying under 9 hours a week Limitations: Abstract only. 121 of 125 infants appear in the group counts. Outcome counted by parent report. Dose, duration, emulsion make-up and funding not given in the abstract. Small single-product trial that has not been repeated by an independent team. Read: abstract
Alhusainy 2010 Identification of nevadensin as an important herb-based constituent inhibiting estragole bioactivation and physiology-based biokinetic modeling of its possible in vivo effect. Toxicol Appl Pharmacol · PMID 20226806 · DOI	Laboratory and modelling study in-vitro	Rat hepatocytes, rat and human liver fractions	Nevadensin (a basil flavonoid) with estragole basil Up to 20 micromolar · vs Estragole alone	Nevadensin blocked the enzyme that activates estragole (Ki 4 nanomolar) and, in models, nearly abolished formation of the carcinogenic metabolite. The authors note a food matrix with such blockers could lower cancer risk compared with pure estragole. Nevadensin is from basil, not fennel. Predicted inhibition above 83% Methods, limits and funding Outcomes: Estragole DNA adducts Limitations: Basil compound; models; abstract only. Read: abstract
Alhusainy 2012 Matrix modulation of the bioactivation of estragole by constituents of different alkenylbenzene-containing herbs and spices and physiologically based biokinetic modeling of possible in vivo effects. Toxicol Sci · PMID 22649189 · DOI	Laboratory and modelling study in-vitro	Herb and spice extracts; human HepG2 cells; computer models	Flavonoids (quercetin, kaempferol, myricetin, apigenin, nevadensin) from alkenylbenzene-containing herbs and spices various herbs Various	Flavonoids blocked this enzyme and reduced DNA adducts in cells, and models predicted lower activation of estragole when it is taken with them. The abstract does not state that fennel itself contains these flavonoids. Not applicable Methods, limits and funding Outcomes: Block of the enzyme (SULT) that makes the cancer-causing estragole metabolite Limitations: Not specific to fennel. Cells and models only. Abstract only. Read: abstract
Anheyer 2017 Herbal Medicines for Gastrointestinal Disorders in Children and Adolescents: A Systematic Review. Pediatrics · PMID 28562281 · DOI	Systematic review	1927 Children and adolescents 0 to 18 years with gastrointestinal disorders; 14 randomised trials	Herbal treatments including fennel oil, fennel tea and fennel-containing compound preparations (for colic), peppermint oil, and others various Various Various · vs Placebo, no treatment or drugs	Evidence was found for different fennel preparations (oil, tea, herbal compound) in treating infantile colic. Peppermint oil helped functional abdominal pain. No serious adverse events were reported. Few studies existed for any one herb. Not pooled Methods, limits and funding Outcomes: Effectiveness and safety of herbs for stomach and bowel disorders in children Limitations: Search to July 2016. Few trials per herb. Only the abstract was read. Funding and conflicts: One author reported grants from herbal-medicine companies (Schwabe Pharma, Steigerwald, Repha); the others reported none (as stated in the record) Read: abstract
Annahazi 2025 Fennel Tea Has a Region-Specific Effect on the Motility of the Stomach. Neurogastroenterol Motil · PMID 41214408 · DOI	Laboratory study (animal tissue) animal	Smooth muscle strips from guinea pig stomach (antrum, corpus, fundus)	Freshly brewed fennel tea, 0.78 to 100 microlitres per mL in an organ bath fruit/seed (tea) 0.78 to 100 microlitres per mL Minutes per exposure · vs Strips before and after tea; blockers (tetrodotoxin, L-NAME, SKF-96365)	Fennel tea relaxed the upper stomach (fundus and corpus) at every concentration and increased the force of contractions in the lower stomach (antrum). The relaxation was blocked by SKF-96365, a store-operated calcium channel blocker, but not by nerve or nitric oxide blockers. Significant relaxation (P<0.05) at all concentrations in fundus and corpus Methods, limits and funding Outcomes: Muscle tone, amplitude and frequency of contractions Limitations: Guinea pig tissue in a dish; not people. The exact target was not identified. Abstract only. Funding and conflicts: Authors declared no conflicts Read: abstract
Asano 2016 Anethole restores delayed gastric emptying and impaired gastric accommodation in rodents. Biochem Biophys Res Commun · PMID 26915803 · DOI	Animal study (mice and rats) animal	Mice with drug-delayed stomach emptying; rats tested for stomach accommodation	Anethole; also fennel oil and Anchu-san (a Japanese herbal medicine containing anethole) fruit/seed (oil, isolated compound) Oral; amounts not in the abstract Single dosing · vs Vehicle	Anethole improved clonidine-induced delayed stomach emptying but did not change normal emptying in mice. Fennel oil and Anchu-san also restored emptying. Anethole stimulated stomach accommodation in rats. Not given as numbers in the abstract Methods, limits and funding Outcomes: Gastric emptying; gastric accommodation (stomach relaxing to hold food) Limitations: Rodent study; isolated compound; abstract only. Read: abstract
Azimi 2022 Efficacy of the herbal formula of Foeniculum vulgare and Rosa damascena on elderly patients with functional constipation: A double-blind randomized controlled trial. J Integr Med · PMID 35339396 · DOI	Randomized controlled trial (double blind, active controlled)	50 Adults over 60 with functional constipation (Rome IV), a hospital clinic in Kerman, Iran; 25 per group finished	Herbal formula of fennel (Foeniculum vulgare) and Damask rose (Rosa damascena). A COMBINATION. fruit/seed (with rose) 10 g sachet in warm water twice a day 4 weeks of treatment plus 4 weeks follow-up · vs Polyethylene glycol 4000 (a standard laxative)	Both groups improved. The herbal formula group had a greater improvement in constipation severity, stool consistency and quality of life (all P<0.001), with milder side effects (mild diarrhoea) and longer relief than PEG 4000. Between-group P<0.001 for all three main outcomes (values not given in the abstract) Methods, limits and funding Outcomes: Constipation severity, stool consistency, constipation quality of life, side effects Limitations: Small trial. Active comparator only, no placebo. Fennel and rose given together. Mechanism unknown. Single centre. Abstract only. Registration: Iranian Registry of Clinical Trials IRCT20200108046056N1 Read: abstract
Bae 2015 Fennel (Foeniculum vulgare) and Fenugreek (Trigonella foenum-graecum) Tea Drinking Suppresses Subjective Short-term Appetite in Overweight Women. Clin Nutr Res · PMID 26251835 · DOI	Randomized crossover trial (single blind, placebo controlled)	9 Nine overweight Korean women	Fennel tea and fenugreek tea fruit/seed (tea) One serving before lunch Single sessions · vs Placebo tea	Fennel tea reduced hunger and prospective food consumption and increased fullness compared with placebo tea (P<0.05) on rating scales. Actual food eaten at lunch did not differ. Ratings improved; food intake no different Methods, limits and funding Outcomes: Subjective appetite (hunger, fullness) and lunch buffet intake Limitations: Only nine women; single meal; subjective ratings only. Funding and conflicts: No conflict declared Read: abstract
Banaei 2025 Effect of fennel extract on Anti-Müllerian Hormone and sonographic indices in infertile women with occult premature ovarian insufficiency: a randomized controlled clinical trial. BMC Complement Med Ther · PMID 41029339 · DOI	Randomized controlled trial (placebo controlled)	60 Infertile women with occult premature ovarian insufficiency, Tabriz, Iran	Fennel extract fruit/seed (extract) Not given in the abstract 60 days · vs Placebo	AMH did not differ (P=0.986). Antral follicle count was 1.6 higher with fennel (95% CI 0.07 to 3.1; P=0.040). AFC mean difference 1.6; AMH no difference (0.07 to 3.1) Methods, limits and funding Outcomes: Anti-Mullerian hormone (AMH) and antral follicle count Limitations: Small; one secondary outcome positive and the main hormone unchanged; no pregnancy outcome. Abstract only. Funding and conflicts: Authors declared no competing interests Registration: IRCT20111219008459N15 Read: abstract
Bergau 2021 Bioactivation of estragole and anethole leads to common adducts in DNA and hemoglobin. Food Chem Toxicol · PMID 34015424 · DOI	Laboratory and human pilot study	Rat and human liver fractions; a pilot with volunteers drinking fennel tea for four weeks	Estragole, anethole; fennel tea rich in both fruit/seed (tea) Not given in the abstract 4 weeks of tea, then washout	Estragole and anethole formed the same type of adducts, anethole at lower levels. In the pilot, haemoglobin adduct levels in volunteers rose significantly during four weeks of fennel tea and fell during washout. Significant rise during consumption Methods, limits and funding Outcomes: Haemoglobin and DNA adducts Limitations: Pilot; number of volunteers not given in the abstract; adducts show exposure, not disease. Abstract only. Read: abstract
Bristol 2011 NTP 3-month toxicity studies of estragole (CAS No. 140-67-0) administered by gavage to F344/N rats and B6C3F1 mice. Toxic Rep Ser · PMID 21445103	Animal toxicity study (rats and mice) animal	F344/N rats and B6C3F1 mice, 10 per sex per group	Estragole (>99% pure) by gavage, 37.5 to 600 mg/kg isolated compound 37.5, 75, 150, 300, 600 mg/kg, 5 days a week 3 months · vs Corn oil vehicle	At 300 and 600 mg/kg weight gain was reduced, rats developed a mild anaemia, and liver enzymes and liver weights rose with liver changes. Relative liver weight rose from 75 mg/kg in females. Effects were stronger in males. Liver weights increased at 75 mg/kg and above (females) Methods, limits and funding Outcomes: Body weight, blood tests, organ weights, liver changes Limitations: Pure estragole at doses far above human exposure; only the first part of the long abstract was read. Abstract only. Read: abstract
Chen 2012 Anethole suppressed cell survival and induced apoptosis in human breast cancer cells independent of estrogen receptor status. Phytomedicine · PMID 22464689 · DOI	Laboratory study (human breast cancer cells) in-vitro	MCF-7 (oestrogen-receptor positive) and MDA-MB-231 (negative) human breast cancer cells	Anethole at about 1 millimolar isolated compound 1 mM Not given · vs Untreated	Anethole reduced survival and triggered cell death in both cell types regardless of oestrogen receptor status. Not given Methods, limits and funding Outcomes: Cell survival and cell-death pathways Limitations: A very high concentration, in a dish. Abstract only. Read: abstract
Chen 2020 Heated fennel therapy promotes the recovery of gastrointestinal function in patients after complex abdominal surgery: A single-center prospective randomized controlled trial in China. Surgery · PMID 32682507 · DOI	Randomized controlled trial (surgeon blinded)	381 Patients after major abdominal surgery for liver/bile duct, pancreatic or stomach tumours, China	HEATED FENNEL PACK applied on the abdomen (an external heat treatment), compared with a heated rice-husk pack. Fennel was NOT swallowed. fruit/seed (external pack) Not given in the abstract After surgery until bowel function returned · vs Heated rice husk pack	Time to first flatus, first defecation and fasting time were shorter with the fennel pack (P<0.05 each). Abdominal distension eased (P<0.001). In patients with bowel reconstruction, hospital stay was 9.25 versus 11.1 days (P=0.023). Hospital stay (reconstruction subgroup) 9.25 +/- 5.1 versus 11.1 +/- 6.4 days Methods, limits and funding Outcomes: Time to first flatus and defecation, fasting time, hospital stay, pain, distension Limitations: The pack is applied on the skin, so the result does not apply to fennel tea or capsules. Heat itself may matter; the comparison pack was also heated but different. Single centre. Subgroup finding. Abstract only. Read: abstract
Delaram 2011 Comparing the Effects of Echinophora-platyloba, Fennel and Placebo on Pre-menstrual Syndrome. J Reprod Infertil · PMID 23926506	Single blind randomized trial	90 Students with moderate to severe PMS, Shahrekord, Iran	Fennel extract versus Echinophora platyloba extract versus placebo fruit/seed (extract) Not given in the abstract Two cycles · vs Placebo	Scores after treatment were 64.4 with fennel versus 79.1 with placebo (49.7 with Echinophora); P<0.001. Fennel and Echinophora were not significantly different. Score 64.4 vs 79.1 (start about 101 vs 104) Methods, limits and funding Outcomes: PMS severity (Daily Record of Severity of Problems) Limitations: Single-blind; abstract does not give dose; 2008 study. Abstract only. Read: abstract
Di Ciaula 2018 Efficacy of bio-optimized extracts of turmeric and essential fennel oil on the quality of life in patients with irritable bowel syndrome. Ann Gastroenterol · PMID 30386118 · DOI	Open pilot (uncontrolled) study	211 Adults with IBS recruited by family doctors (14% diarrhoea-predominant, 24% constipation-predominant, 62% mixed)	Enterofytol: bio-optimised turmeric extract plus fennel essential oil. A COMBINATION product. fruit/seed (essential oil) 2 capsules twice a day for one month, then 2 capsules once a day 2 months	IBS severity fell and quality of life improved in all three IBS subtypes. People with diarrhoea-predominant IBS started worst and improved most. Not given as a number in the abstract Methods, limits and funding Outcomes: IBS severity index and quality of life Limitations: No control group, so placebo response and natural change cannot be separated. Combination product. The record lists no conflicts, but some authors appear to have links to the product company; this was not checked. Read: abstract
Ding 2015 In vivo genotoxicity of estragole in male F344 rats. Environ Mol Mutagen · PMID 25361439 · DOI	Animal study (rats) animal	Male F344 rats	Estragole 300, 600 or 1,000 mg/kg by mouth; safrole for comparison isolated compound 300 to 1,000 mg/kg at 0, 24 and 45 hours 48 hours · vs Corn oil	Estragole caused dose-dependent DNA damage in the liver (the organ where it causes cancer in rodents) but not in the stomach, and no micronuclei in blood. Oxidative damage appeared to contribute. Dose-dependent liver DNA damage Methods, limits and funding Outcomes: DNA damage in liver and stomach; micronuclei Limitations: Very high single doses in rats. Abstract only. Read: abstract
EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) 2023 Safety and efficacy of feed additives consisting of essential oils from the fruit and stems of Foeniculum vulgare Mill. ssp. vulgare: Bitter fennel oil for use in all animal species and sweet fennel oil for use in dogs and cats (FEFANA asbl). EFSA J · PMID 37908453 · DOI	Regulatory/scientific opinion n/a	Bitter fennel oil and sweet fennel oil used as animal feed flavourings	Fennel essential oils (estragole up to 6.1% in bitter oil, up to 5.0% in sweet oil) fruit and stem essential oil Feed levels	The oils are irritants to skin and eyes and are dermal and respiratory sensitisers. Because estragole is over 1%, fennel oils are classified as suspected of causing genetic defects and cancer and should be handled accordingly. Not applicable Methods, limits and funding Outcomes: Safety for animals, consumers and handlers Limitations: An opinion on animal feed use, not on human supplements. Abstract only. Funding and conflicts: EFSA panel opinion Read: abstract
Eliasvandi 2019 Effect of an herbal capsule on chronic constipation among menopausal women: A randomized controlled clinical trial. Avicenna J Phytomed · PMID 31763211 · DOI	Randomized controlled trial (triple blind, placebo controlled)	64 Postmenopausal women with chronic constipation, Iran	Traditional herbal capsule of many ingredients including Roman anise, green anise or fennel, cloves, violet, Terminalia chebula, raisins, Alhagi maurorum, SENNA LEAVES and golqand. A MANY-HERB COMBINATION that contains a stimulant laxative (senna). mixed Not given in the abstract Not given in the abstract · vs Placebo	Bowel movements were more frequent on the herbal capsule than placebo (mean difference 4.2). Straining and other symptoms fell more (P<0.001). Mean difference in bowel movement frequency 4.2; symptom score difference -15.4 (Bowel frequency CI as printed 0.3 to 4.5 (inconsistent with the mean difference of 4.2; quoted as printed); symptom score CI -19.29 to -11.5) Methods, limits and funding Outcomes: Bowel movement frequency and constipation symptom scores Limitations: Fennel is one of about ten ingredients and senna is a known laxative, so the result says nothing specific about fennel. The printed confidence interval does not match the mean difference. Funding and conflicts: Authors declared no conflict of interest Read: abstract
Foong 2020 Oral galactagogues (natural therapies or drugs) for increasing breast milk production in mothers of non-hospitalised term infants. Cochrane Database Syst Rev · PMID 32421208 · DOI	Systematic review and meta analysis (Cochrane)	3005 Breastfeeding mothers of healthy term infants; 41 randomised trials of oral galactagogues, 27 of natural ones including fennel	Natural galactagogues (banana flower, fennel, fenugreek, ginger, moringa, shatavari and others) and drugs various Various Various · vs Placebo or no treatment	Certainty of evidence was low to very low. For fennel specifically, the review is "very uncertain" whether fennel or fenugreek improves infant weight. Natural galactagogues may help infant weight and milk volume in some subgroup analyses, but magnitude is very uncertain. Milk volume results could not be pooled (I2 99%). Reported adverse effects were minor (e.g. maple-syrup-smelling urine, urticaria in infants). Not pooled for fennel Methods, limits and funding Outcomes: Continued breastfeeding, infant weight, milk volume, adverse effects Limitations: Judged low to very low certainty by Cochrane (high risk of bias, large inconsistency, imprecision). Only the abstract was read. Read: abstract
Félix 2026 Effect of Aromatherapy Massage With Foeniculum vulgare Mill. Seed Essential Oil Compared to Massage on Anxiety, Well-Being, and Sleep Quality: An Exploratory Randomized Study. Health Sci Rep · PMID 42147465 · DOI	Randomized exploratory study	40 Adult participants (country not stated in the abstract; authors are from Portugal)	Massage with 1.6% fennel seed essential oil in sweet almond oil (aromatherapy massage; 78.2% trans-anethole in the oil) versus massage with almond oil alone fruit/seed (essential oil, skin and inhaled) Massage every 15 days 2 months · vs Massage with almond oil only	State anxiety was lower in the fennel oil group after the last session (32.47 versus 41.75; difference -9.28, P=0.007). Sleep and well-being differences did not reach statistical significance. State anxiety difference -9.28 (Not given) Methods, limits and funding Outcomes: State anxiety (STAI), sleep (PSQI), well-being (WHO-5) Limitations: Exploratory; 40 people; no change over time within groups (P=0.536 and 0.381), which makes the between-group difference hard to interpret; skin and aroma exposure, not swallowed. Read: abstract
Gavish 2023 A real-world evaluation of an herbal treatment for infantile colic reported by 1218 parents in Israel. J Pediatr Nurs · PMID 36528454 · DOI	Observational study (retrospective online survey, case control)	1218 Parents of babies with colic in Israel; 771 used a fennel-based product, the rest used nothing	BabyCalm, a fennel-based commercial herbal product (Hisunit Ltd., Israel) Not given in the abstract Not given in the abstract · vs Parents who used no product	Parents rated the treatment successful in 65% of cases and reported clear improvement within 30 minutes for 69% to 79% of symptoms. Fewer colic symptoms were reported by users than non-users. Perceived success 65% Methods, limits and funding Outcomes: Parent-perceived treatment success and symptom improvement Limitations: Parent opinion collected after the fact, not blinded, no placebo, parents chose whether to use the product. Cannot show the product caused the improvement. Funding and conflicts: Two authors were paid scientific consultants of the product maker (stated in the record) Read: abstract
Ghafarzadegan 2025 Efficacy of an Iranian herbal medicine formula for postoperative constipation in trauma patients with hip and lower limb fractures: A triple-blind, placebo-controlled randomized clinical trial. Int J Orthop Trauma Nurs · PMID 39951927 · DOI	Randomized controlled trial (triple blind, placebo controlled)	61 Patients with constipation after surgery for hip or leg fractures, Kashan, Iran	Herbal Laxative Capsule: SENNA (Cassia angustifolia), Aloe vera, fennel, coriander, caraway. A MANY-HERB COMBINATION that includes two known laxative plants. mixed 520 mg capsule twice a day 1 week · vs Placebo	Constipation severity and stool consistency improved more with the capsule than placebo (P<0.001). No significant adverse effects were reported. P<0.001 (values not given in the abstract) Methods, limits and funding Outcomes: Constipation severity, stool consistency, patient satisfaction Limitations: Senna and aloe are established laxatives, so the result says nothing specific about fennel. Short, small trial. Abstract only. Funding and conflicts: Authors declared no competing interests Read: abstract
Ghaffari 2020 The effect of Fennel seed powder on estradiol levels, menopausal symptoms, and sexual desire in postmenopausal women. Menopause · PMID 33110044 · DOI	Randomized controlled trial	80 Postmenopausal women aged 45 to 60, Yasuj, Iran	Fennel seed powder fruit/seed (powder) 4 capsules a day (2 g) 8 weeks · vs Starch capsules	Menopausal symptom score fell from 30.8 to 19 in the fennel group and from 31.2 to 26.4 in the control group (P<0.05). Sexual desire did not change significantly. Estradiol fell in both groups (60.4 to 52.6 on fennel, 55.1 to 39.9 on control); the difference between groups was not significant. Symptom score -11.8 versus -4.8 points (own subtraction); estradiol not different between groups Methods, limits and funding Outcomes: Kupperman index (menopausal symptoms), sexual desire (Hurlbert index), blood estradiol Limitations: Abstract does not say whether the trial was blinded. Abstract only. Read: abstract
Ghavi 2023 Comparison of the Effect of Fennel and Evening Primrose Oil on Menopausal Problems and Hormonal Levels: A Randomized Controlled Trial. Iran J Nurs Midwifery Res · PMID 37694196 · DOI	Randomized controlled trial (triple blind)	125 Postmenopausal women, Iran	Fennel or evening primrose oil, versus placebo fruit/seed Twice daily 8 weeks · vs Placebo	FSH and estradiol changed significantly in the fennel and evening primrose groups versus placebo (P<0.001). The abstract does not state which direction. MRS scores did not differ between fennel and evening primrose after treatment. Hormone changes P<0.001 (direction not given in the abstract) Methods, limits and funding Outcomes: FSH, estradiol and Menopause Rating Scale Limitations: The abstract does not say whether hormones rose or fell, so it cannot be used to support or rule out an oestrogen-like effect. Abstract only. Funding and conflicts: Nothing to declare Read: abstract
Ghavi 2023 "Ferula assa-foetida L" or "Foeniculum vulgare"? Which one is more effective in the management of polycystic ovarian syndrome? A randomized, placebo controlled, triple-blinded. Avicenna J Phytomed · PMID 37655000 · DOI	Randomized controlled trial (triple blind, placebo controlled)	47 Women with PCOS, Iran	Fennel 46 mg twice a day or Ferula assa-foetida 100 mg, or placebo fruit/seed (extract) 46 mg twice a day 3 months · vs Placebo	Ovarian follicle numbers were lower in fennel and ferula groups than placebo (P<0.05). Only Ferula changed DHEAS and TSH significantly. Authors conclude Ferula was more effective than fennel. Follicle count lower versus placebo (P<0.05) Methods, limits and funding Outcomes: Ovarian follicle count (ultrasound), hormones Limitations: Very small groups (14 to 15). Funding: authors state no tie to Barij Essence Company. Funding and conflicts: Authors declared no financial or technical relationship with Barij Essence Company Read: abstract
Ghazanfarpour 2017 Effect of Foeniculum vulgare (fennel) on vaginal atrophy in postmenopausal women: A double-blind, randomized, placebo-controlled trial. Post Reprod Health · PMID 28990439 · DOI	Randomized controlled trial (double blind, placebo controlled)	60 Postmenopausal women with vaginal atrophy, Mashhad, Iran	Oral fennel fruit/seed Not given in the abstract 3 months · vs Placebo	Both groups improved from baseline, but there was no significant difference between fennel and placebo for any cell type (e.g. superficial cells P=0.82). The authors conclude oral fennel had no significant positive effect. No between-group difference (P=0.19 to 0.82) Methods, limits and funding Outcomes: Maturation Vaginal Index (cell counts on a vaginal smear) Limitations: Small; the authors suggest higher doses might be needed; abstract only. Read: abstract
Ghazanfarpour 2018 A double-blind, placebo-controlled trial of Fennel (Foeniculum vulgare) on menopausal symptoms: A high placebo response. J Turk Ger Gynecol Assoc · PMID 29755029 · DOI	Randomized controlled trial (double blind, placebo controlled)	50 Postmenopausal women, Mashhad, Iran	Oral fennel fruit/seed Not given in the abstract 3 months · vs Placebo	Both groups improved on hot flushes, night sweats, sweating, anxiety and depressed mood. No difference between fennel and placebo except for one item (coughing and sneezing when urinating, P=0.03). Authors blame a high placebo response. No significant difference between groups on most items Methods, limits and funding Outcomes: Menopause-Specific Quality of Life questionnaire Limitations: Small; high placebo response. Abstract only. Funding and conflicts: Authors declared no conflict of interest Read: abstract
Ghazanfarpour 2018 Effect of Foeniculum vulgare (fennel) on symptoms of depression and anxiety in postmenopausal women: a double-blind randomised controlled trial. J Obstet Gynaecol · PMID 28891367 · DOI	Randomized controlled trial (double blind, placebo controlled)	60 Postmenopausal women, Iran	Fennel fruit/seed Not given in the abstract Not given in the abstract · vs Placebo	No significant fall in the whole group. In women who had anxiety or depression at the start, scores showed a borderline or significant improvement. Whole group: no significant difference Methods, limits and funding Outcomes: Anxiety and depression scores (HADS, Zung scale) Limitations: Subgroup finding; small; abstract only. Read: abstract
Ghodsi 2014 The effect of fennel on pain quality, symptoms, and menstrual duration in primary dysmenorrhea. J Pediatr Adolesc Gynecol · PMID 25085020 · DOI	Randomized clinical trial (no treatment control)	80 Female students with primary dysmenorrhoea, Iran	Fennel soft capsule fruit/seed One 30 mg capsule every 4 hours from 3 days before menstruation to the 5th day 3 months · vs No medication	Nausea and weakness were lower and period length shorter after 2 and 3 months with fennel. Well-being improved. Not given as numbers for pain in the abstract Methods, limits and funding Outcomes: Pain (visual scale, McGill questionnaire), symptoms, menstrual duration, well-being Limitations: No placebo, so people knew they were treated. The abstract does not report a pain score difference clearly. Abstract only. Read: abstract
Gori 2012 Can estragole in fennel seed decoctions really be considered a danger for human health? A fennel safety update. Evid Based Complement Alternat Med · PMID 22899959 · DOI	Narrative review in-vitro	Fennel safety literature on estragole in decoctions	Fennel seed decoctions fruit/seed	The authors argue that estragole in a decoction is part of a mixture and that pure estragole is inactivated by other substances in the decoction, so the cancer risk from decoctions may be overstated. They note the classic use of fennel infusions for infant colic. Not applicable Methods, limits and funding Outcomes: Whether estragole in fennel decoctions is a real danger Limitations: Opinion review (Italian herbal-medicine researchers); the EMA does not adopt this view in its limits. Abstract only. Read: abstract
Gumus 2023 Assessment of Toxic Pyrrolizidine and Tropane Alkaloids in Herbal Teas and Culinary Herbs Using LC-Q-ToF/MS. Foods · PMID 37835225 · DOI	Laboratory survey in-vitro	Herbal teas and culinary herbs sold in Turkish markets	Many herbal teas including fennel tea fruit/seed (tea)	At least a few of these toxic plant alkaloids were found in every product tested. Total contents across black, green, mixed, flavoured, chamomile, sage, linden, fennel, rosehip, peppermint and thyme samples ranged from 4.6 to 1,054.5 ng per g. The abstract does not give a separate figure for fennel tea. Range 4.6 to 1,054.5 ng/g across all teas Methods, limits and funding Outcomes: Pyrrolizidine and tropane alkaloids Limitations: No separate fennel result in the abstract; one country. Abstract only. Funding and conflicts: Author declared no conflict of interest Read: abstract
Harb 2016 Infant Colic-What works: A Systematic Review of Interventions for Breast-fed Infants. J Pediatr Gastroenterol Nutr · PMID 26655941 · DOI	Systematic review and meta analysis	Breastfed or mixed-fed infants under 6 months with colic; 17 randomised trials	Interventions for colic; subgroup of 3 trials of preparations containing fennel (oil) fruit/seed (oil) Various Various · vs Placebo or other	In the 3 fennel-containing trials the pooled difference in crying time was -72.1 minutes a day. Probiotics (Lactobacillus reuteri) gave -55.8 minutes a day at day 21 across 6 trials. Fennel preparations: mean difference -72.1 min/day (95% CI -126.4 to -17.7) Methods, limits and funding Outcomes: Crying time (minutes a day) Limitations: Only three small trials were pooled and they used different fennel products (including a three-herb combination). The authors note limitations and call for better trials. Only the abstract was read. Read: abstract
Hawrelak 2020 Western herbal medicines in the treatment of irritable bowel syndrome: A systematic review and meta-analysis. Complement Ther Med · PMID 31987249 · DOI	Systematic review and meta analysis	Adults with IBS; 33 double-blind placebo-controlled trials of Western herbal medicines (17 on peppermint oil)	Western herbal medicines, including the combination of curcumin and Foeniculum vulgare oil, Pimpinella anisum oil, and others various Various Various · vs Placebo	Peppermint oil, Aloe vera and asafoetida were effective in pooled analyses. The curcumin plus fennel oil combination was among those that showed efficacy in a single well-designed trial. Apart from peppermint oil, Aloe vera and asafoetida, none of the positive trials had been repeated. Not pooled for fennel Methods, limits and funding Outcomes: IBS symptoms and quality of life Limitations: Fennel only appears as one unreplicated combination trial. Only the abstract was read. Read: abstract
Javidnia 2003 Antihirsutism activity of Fennel (fruits of Foeniculum vulgare) extract. A double-blind placebo controlled study. Phytomedicine · PMID 13678227 · DOI	Randomized controlled trial (double blind)	38 Women with idiopathic hirsutism (excess hair), Shiraz, Iran	Topical cream with 1% or 2% fennel fruit ethanol extract, or placebo cream fruit/seed (cream) 1% and 2% cream Not given in the abstract · vs Placebo cream	Hair diameter fell 7.8% (1%), 18.3% (2%) and -0.5% (placebo). Hair diameter -7.8% and -18.3% versus +0.5% Methods, limits and funding Outcomes: Hair diameter Limitations: Only 38 patients; 2003; duration not given in the abstract; applied on the skin. Read: abstract
Jenabi 2023 Effect of Fennel-Valerian Extract on Hot Flashes and Sleep Disorders in Postmenopausal Women: A Randomized Trial. J Menopausal Med · PMID 37160299 · DOI	Randomized trial	76 Postmenopausal women with hot flashes and sleep problems, Iran	Fennel-valerian extract, 500 mg capsule. A TWO-HERB COMBINATION. fruit/seed (with valerian) One 500 mg capsule twice a day 8 weeks · vs Starch placebo capsule	Hot flash frequency and severity were lower than control at one and two months (P<0.05). PSQI score lower than control at two months (P=0.030). Hot flash duration rose in both groups. P<0.05 for frequency and severity Methods, limits and funding Outcomes: Hot flash frequency, severity, duration; sleep (PSQI) Limitations: Combination with valerian (a sleep herb); abstract does not state blinding; abstract only. Funding and conflicts: No conflicts declared Read: abstract
Jourshari 2024 A comparative study of fennel and dimethicone capsule effects on flatulence rate after cesarean section: A double-blind randomized controlled trial. J Educ Health Promot · PMID 39309989 · DOI	Randomized controlled trial (double blind)	Women with flatulence after a caesarean section, teaching hospital in Iran (group sizes not given in the abstract)	Fennel capsules versus dimethicone (simethicone-type anti-gas medicine) capsules One dose every 6 hours for four doses after oral feeding restarted About 1 day (four doses) · vs Dimethicone	Flatulence fell in both groups. After adjusting for the starting level, there was no difference between fennel and dimethicone. No between-group difference (F(1,72)=0.27, P=0.607) Methods, limits and funding Outcomes: Flatulence rating on a 0-10 style visual analogue scale before and one hour after each dose Limitations: No placebo group, so a fall in gas that would have happened anyway cannot be ruled out. Fennel dose and product not given in the abstract. Small hospital trial. Abstract only. Funding and conflicts: Authors declared no financial or other interests Read: abstract
Kamali 2025 Fennel (Foeniculum vulgare) oral capsules improve endometrial thickness in infertile women following clomiphene citrate treatment. Eur J Obstet Gynecol Reprod Biol · PMID 40784268 · DOI	Randomized controlled trial	60 Infertile women taking clomiphene citrate, Iran	Fennel capsules, 60 mg per day fruit/seed 60 mg/day During the clomiphene treatment cycle (length not given) · vs No capsule (control group)	Endometrial lining was about 1.7 mm thicker with fennel (P<0.001). Follicle number and size did not differ. Pregnancy rates 16% versus 3% were not significantly different. Endometrial thickness +1.7 mm Methods, limits and funding Outcomes: Endometrial thickness, follicles, pregnancy Limitations: No placebo; an ultrasound measure, not live births; small; abstract only. Funding and conflicts: Authors declared no competing interests Registration: IRCT20241118063767N2 Read: abstract
Kerekes 2019 Furocoumarin Content of Fennel-Below the Safety Threshold. Molecules · PMID 31387269 · DOI	Laboratory analysis (chemistry) in-vitro	33 33 fennel fruit samples of different origins	Fennel fruit (psoralen, bergapten and imperatorin measured by LC-MS) fruit/seed Highest EMA-monograph dose used for the calculation	At the highest therapeutic dose in the EU monograph the furocoumarin intake from the samples reached up to 1.22 micrograms a day, which is below the most restrictive recommendations. The authors conclude fennel is safe in this respect. Up to 1.22 micrograms a day Methods, limits and funding Outcomes: Furocoumarin (a sun-sensitising compound family) content Limitations: Measures content, not skin reactions in people. Did not look at essential oil or at skin contact with fresh plant. Abstract only. Funding and conflicts: Authors declared no conflict of interest Read: abstract
Khan 2024 Effect of Salvia hispanica (Chia seeds) and Foeniculum vulgare (Fennel seeds) against weight-loss and lipid profile in obese human subjects. Pak J Pharm Sci · PMID 38747274	Randomized controlled trial	Obese adults aged 25 to 40, Jinnah Hospital Lahore	Chia seeds PLUS fennel seeds. A TWO-SEED COMBINATION. fruit/seed (with chia) Not given in the abstract 3 months · vs Placebo	The authors report significant (P<0.05) improvements in BMI, LDL, HDL, triglycerides and total cholesterol. No numbers in the abstract. Not given Methods, limits and funding Outcomes: BMI and blood lipids Limitations: Two seeds given together, so fennel cannot be singled out; no numbers, group sizes or doses in the abstract. Abstract only. Read: abstract
Lee 2015 Foeniculum vulgare Mill. Protects against Lipopolysaccharide-induced Acute Lung Injury in Mice through ERK-dependent NF-κB Activation. Korean J Physiol Pharmacol · PMID 25729281 · DOI	Animal study (mice) animal	Mice with lipopolysaccharide-induced acute lung injury	Foeniculum vulgare extract (125, 250 or 500 microlitres/kg, by injection) fruit/seed (extract) 125 to 500 microlitres/kg by injection Single dose before injury · vs Dexamethasone; vehicle	Fennel lowered inflammatory cells and cytokines dose-dependently and reduced ERK phosphorylation. Not given as numbers in the abstract Methods, limits and funding Outcomes: Inflammatory cells, IL-6, TNF-alpha, MMP-9, nitric oxide Limitations: Given by injection (not swallowed) to mice; abstract only. Read: abstract
Lee 2020 Fennel for Reducing Pain in Primary Dysmenorrhea: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrients · PMID 33182553 · DOI	Systematic review and meta analysis	Women with primary dysmenorrhoea; 12 randomised trials	Fennel (various forms) versus placebo or conventional pain drugs fruit/seed Various Various · vs Placebo or conventional drugs (e.g. mefenamic acid)	Seven trials (n=502) found fennel similar to conventional drugs for pain (SMD 0.07, 95% CI -0.08 to 0.21, I2 0%). Versus placebo (n=468) fennel reduced pain (SMD -3.27, 95% CI -5.28 to -1.26) but with very high inconsistency (I2 98%). Only three trials checked side effects; one reported minor ones. Risk of bias moderate; publication bias suspected. Versus drugs SMD 0.07; versus placebo SMD -3.27 (Versus drugs -0.08 to 0.21; versus placebo -5.28 to -1.26) Methods, limits and funding Outcomes: Menstrual pain Limitations: I2 of 98% against placebo means trials disagree greatly, so the pooled number should not be trusted as a size. Many small trials with favourable results (possible publication bias). Mostly Iranian. Abstract only. Funding and conflicts: Authors declared no conflict of interest Read: abstract
Lee 2021 Fennel (Foeniculum vulgare Miller) for the management of menopausal women's health: A systematic review and meta-analysis. Complement Ther Clin Pract · PMID 33725577 · DOI	Systematic review and meta analysis	Menopausal women; 7 randomised trials of fennel	Fennel (various) versus placebo fruit/seed Various Various · vs Placebo	Two trials against placebo (n=145) favoured fennel for menopausal symptoms (SMD -1.32, 95% CI -1.76 to -0.87). Other trials found no benefit for sexual function, quality of life or psychological health. No serious adverse events. Concerning risk of bias in general. Menopausal symptoms SMD -1.32 (-1.76 to -0.87) Methods, limits and funding Outcomes: Menopausal symptoms, sexual function, quality of life, mood Limitations: Only two trials in the pooled result, both small, with concerning risk of bias. Abstract only. Read: abstract
Levorato 2018 In vitro toxicity evaluation of estragole-containing preparations derived from Foeniculum vulgare Mill. (fennel) on HepG2 cells. Food Chem Toxicol · PMID 29233689 · DOI	Laboratory study (human liver cells) in-vitro	HepG2 human liver cancer cells	Fennel seed powder and fennel seed essential oil fruit/seed Several concentrations Not given in the abstract · vs Untreated	Fennel seed powder caused no DNA damage, cell death or cell cycle change. The essential oil caused no DNA damage but did produce marked dose-dependent cell death and cell cycle arrest at the highest dose. The authors suggest estragole genotoxicity may be reduced in whole botanical mixtures. No DNA damage with either Methods, limits and funding Outcomes: DNA damage, cell death, cell cycle Limitations: Cells in a dish; abstract only. Read: abstract
Liu 2026 Rapid Detection and Deep Characterization of Adulterants in Fennel Essential Oil Using Electronic Nose With GC-MS/Chemometrics. J Food Sci · PMID 42340018 · DOI	Laboratory study (analytical chemistry) in-vitro	Fennel essential oil and four adulterants	Fennel essential oil adulterated with anise, dill, caraway or cumin oils fruit/seed (essential oil)	The authors state fennel essential oil is at risk of fraud because of high value and demand, and developed methods that detected adulteration above 30% with 100% accuracy. Not applicable Methods, limits and funding Outcomes: Detecting adulteration Limitations: Method paper. Abstract only. Read: abstract
Ma 2015 [The Effect of Fennel Tea Drinking on Postoperative Gut Recovery after Gynecological Malignancies Operation]. Sichuan Da Xue Xue Bao Yi Xue Ban · PMID 26867333	Randomized controlled trial	159 Women after abdominal surgery for gynaecological cancers, Sichuan, China (article in Chinese)	Fennel fruit tea (Fructus Foeniculi), 5 g of dried fruit in 130 mL of boiling water, filtrate only, twice a day from the morning after surgery until first flatus. Control: plain water. fruit/seed 5 g fruit per cup, twice a day Until first passing of gas · vs Water	Hospital stay 5.6 versus 6.7 days, time to flatus 53.1 versus 64.2 hours, time to first bowel movement 4.3 versus 5.4 days (all P<0.001, tea versus water). Ileus symptoms were more common in the control group (relative risk 2.6). Time to flatus about 11 hours shorter (own subtraction); ileus relative risk 2.6 (Ileus relative risk 95% CI 1.5 to 4.5) Methods, limits and funding Outcomes: Time to first flatus and first bowel movement, hospital stay, ileus symptoms Limitations: Not blinded in an obvious way (tea versus water). Single Chinese centre. Abstract only. Tea given to adult cancer surgery patients, which is not the same as use in healthy people. Read: abstract
Mahdavian 2019 Effect of the Mixed Herbal Medicines Extract (Fennel, Chamomile, and Saffron) on Menopause Syndrome: a Randomized Controlled Clinical Trial. J Caring Sci · PMID 31598511 · DOI	Randomized controlled trial (triple blind, placebo controlled)	120 Perimenopausal women aged 45 to 65, Iran	Drops of mixed extract: chamomile, fennel and saffron. A THREE-HERB COMBINATION. fruit/seed (with chamomile and saffron) Group A: 250 mg chamomile, 30 mg fennel, 15 mg saffron; B: 1000, 120, 60 mg; D: 500, 60, 30 mg 12 weeks · vs Placebo	Physical, psychological and urogenital scores improved in groups B and D, not in group A or placebo. The high-dose group B improved most (effect size 0.92). Effect size 0.92 (group B) Methods, limits and funding Outcomes: Menopause Rating Scale Limitations: Three-herb mix; the lowest dose did not work; funding not stated; abstract only. Read: abstract
Martins 2012 Estragole: a weak direct-acting food-borne genotoxin and potential carcinogen. Mutat Res · PMID 22561883 · DOI	Laboratory study (cells) in-vitro	V79 and CHO hamster cells	Estragole fruit/seed (isolated compound) Not given Up to 24 hours · vs Untreated	Estragole was a weak direct-acting genotoxin without needing liver enzymes: it caused DNA strand breaks and formed DNA adducts in a dose-dependent way, and damage was partly repaired. Dose-dependent DNA adducts Methods, limits and funding Outcomes: DNA damage, DNA adducts, apoptosis Limitations: Cell lines; isolated compound at high concentration. Abstract only. Read: abstract
Mihats 2017 Levels of estragole in fennel teas marketed in Austria and assessment of dietary exposure. Int J Food Sci Nutr · PMID 27917696 · DOI	Chemical analysis and exposure assessment in-vitro	42 42 fennel teas on the Austrian market	Fennel teas fruit/seed (tea) Typical servings (model)	Estimated estragole exposure was 0.25 to 5.04 micrograms per kg a day for children, 0.32 to 6.42 for women, 0.15 to 2.93 for men and 0.008 to 20.78 for infants. Nearly half of the teas gave MOEs above 10,000, but some were below, indicating a priority for risk management. Teas are used only briefly, so the authors say the estimates are probably conservative. Infant exposure up to 20.78 micrograms per kg per day Methods, limits and funding Outcomes: Estragole in teas; daily exposure; margin of exposure Limitations: Exposure model; one national market. Abstract only. Read: abstract
Modaress Nejad 2006 Comparison of the effectiveness of fennel and mefenamic acid on pain intensity in dysmenorrhoea. East Mediterr Health J · PMID 17037712	Randomized controlled trial	110 High-school girls (mean age 13) with dysmenorrhoea, Kerman, Iran	Fennel extract fruit/seed Not given in the abstract 2 months · vs Mefenamic acid	Complete pain relief or pain decrease in 80% on fennel and 73% on mefenamic acid; no longer needed to rest 80% versus 62%. No significant difference between groups. No significant difference between fennel and mefenamic acid Methods, limits and funding Outcomes: Pain relief Limitations: No placebo group; dose not given; older (2002) study; abstract only. Read: abstract
Mohebbi-Kian 2014 Efficacy of fennel and combined oral contraceptive on depot medroxyprogesterone acetate-induced amenorrhea: a randomized placebo-controlled trial. Contraception · PMID 24981150 · DOI	Randomized controlled trial (double blind, double dummy, placebo controlled)	78 Married women in Hamadan, Iran, with no periods for 45 to 140 days after depot medroxyprogesterone (DMPA) contraceptive injections	Fennel capsules (two a day) for 21 days; a low-dose combined oral contraceptive; or placebo fruit/seed (capsule) Two capsules a day 21 days; bleeding followed for 40 days · vs Placebo	Bleeding occurred in 73% on fennel, 81% on the pill and 19% on placebo (fennel relative risk 3.1, 95% CI 1.6 to 6.2). Mean bleeding amount was higher with fennel (21 cc) than with the pill (14 cc) or placebo (12 cc). More women on fennel (73%) had the next DMPA injection than on placebo (31%). Bleeding RR 3.1 (fennel versus placebo) (1.6 to 6.2) Methods, limits and funding Outcomes: Menstrual bleeding and continuing the DMPA method Limitations: Small trial. It shows fennel can bring on bleeding and larger blood loss in women on a hormonal injection, which is a hormone-active effect. Read: abstract
Mokaberinejad 2019 The comparison of fennel infusion plus dry cupping versus metformin in management of oligomenorrhoea in patients with polycystic ovary syndrome: a randomised clinical trial. J Obstet Gynaecol · PMID 30856025 · DOI	Randomized clinical trial	61 Women with oligomenorrhoea (infrequent periods) and polycystic ovary syndrome (PCOS), Iran	Fennel seed infusion PLUS dry cupping (a Persian-medicine treatment) versus metformin fruit/seed (infusion) Not given in the abstract 6 months · vs Metformin	Days between periods after 3 and 6 months: 32.6 and 30.7 with fennel plus cupping versus 40.7 and 43.2 (the abstract prints "431.22") with metformin. Pain fell more with fennel plus cupping. Cycle length about 31 versus 41-43 days Methods, limits and funding Outcomes: Days between periods; BMI; pain Limitations: Two treatments given together, so fennel cannot be separated from cupping; no placebo; open-label; the abstract contains a typing error ("431.22"). Read: abstract
Monien 2019 Detection of N-Acetyl-S-[3'-(4-methoxyphenyl)allyl]-l-Cys (AMPAC) in Human Urine Samples after Controlled Exposure to Fennel Tea: A New Metabolite of Estragole and trans-Anethole. Chem Res Toxicol · PMID 31565931 · DOI	Human exposure study (controlled)	12 12 healthy adult volunteers (6 women, 6 men), Germany	Fennel tea, 500 mL containing 2.2 mg estragole; one volunteer also took isolated trans-anethole fruit/seed (tea) 500 mL tea (2.2 mg estragole) Single dose; urine collected for 8 hours	Before the tea AMPAC was undetectable. It appeared in the first hour, had a half-life of about 1.1 hours and was almost fully cleared in 8 hours. Total excreted ranged from 93 to 1,076 nanograms, showing large differences between people. Trans-anethole produced much less of it. AMPAC 93 to 1,076 ng total (Not given) Methods, limits and funding Outcomes: Urinary AMPAC, a breakdown product that shows the body detoxified the reactive estragole metabolite Limitations: Shows exposure and handling of estragole, not harm. Small number of healthy volunteers. Abstract only. Read: abstract
Motevalli Haghi 2024 Evaluation of the effect of Foeniculum vulgare fruit and Echium amoenum flower combination on the severity of physical and psychological symptoms of premenstrual syndrome. Avicenna J Phytomed · PMID 40255949 · DOI	Randomized controlled trial (triple blind)	80 Women with premenstrual syndrome, Iran	Fennel fruit 1 g/day plus Echium amoenum (Persian borage) flower 2 g/day. A TWO-HERB COMBINATION. fruit/seed (with borage flower) Fennel 1 g/day with Echium 2 g/day in the second half of the cycle 2 cycles · vs Placebo	All subscales of the daily symptom record were better than placebo at one and two months. Bleeding volume rose in the herb group at 2 months (P<0.05). Between-group P<0.05 on DRSP subscales Methods, limits and funding Outcomes: PMS scales (PSST, DRSP) and quality of life (SF-36) Limitations: Two-herb combination. The increase in bleeding volume is a possible side effect. Abstract only. Funding and conflicts: Authors declared no conflict of interest Read: abstract
Murone 2005 Severe methemoglobinemia due to food intoxication in infants. Pediatr Emerg Care · PMID 16096602 · DOI	Case report (four cases)	4 Four infants with methaemoglobinaemia (blood that cannot carry oxygen properly), Switzerland	Homemade fennel purée that had been improperly handled or stored bulb/vegetable purée Hours before illness	All four infants ate homemade fennel purée a few hours earlier, were treated with methylene blue and recovered fully. The authors conclude that improper handling and storage of vegetables can lead to life-threatening methaemoglobinaemia. Four cases Methods, limits and funding Outcomes: Blue skin (cyanosis) not responding to oxygen Limitations: Describes cooked fennel vegetable, not seed or tea. The abstract does not name the cause beyond handling and storage. Abstract only. Read: abstract
Murphy 2024 Authentication of Fennel, Star Anise, and Anise Essential Oils by Gas Chromatography (GC/MS) and Stable Isotope Ratio (GC/IRMS) Analyses. Plants (Basel) · PMID 38256767 · DOI	Laboratory study (analytical chemistry) in-vitro	45 15 authentic reference oils and 30 commercial samples of anethole-containing oils (fennel, star anise, anise)	Fennel, star anise and anise essential oils fruit/seed (essential oil)	Of the 30 commercial samples analysed, 27% were adulterated, in various ways. 27% of commercial samples adulterated Methods, limits and funding Outcomes: Authenticity Limitations: Mixed oils, not fennel only; 30 samples. Abstract only. Funding and conflicts: Authors declared no conflict of interest Read: abstract
Nadjarzadeh 2021 Effect of hypocaloric high-protein, low-carbohydrate diet supplemented with fennel on androgenic and anthropometric indices in overweight and obese women with polycystic ovary syndrome: A randomized placebo-controlled trial. Complement Ther Med · PMID 33271298 · DOI	Randomized placebo controlled trial (factorial)	64 Overweight or obese women with PCOS, Iran	Fennel capsules (2 a day) with a low-calorie diet (standard or high-protein) fruit/seed 2 capsules a day Not given in the abstract · vs Placebo capsules	Adding fennel to the high-protein diet did not significantly change outcomes. There was a significant interaction between the high-protein diet and fennel on weight (P=0.019). No significant added benefit Methods, limits and funding Outcomes: Weight, BMI and androgen levels Limitations: Only 16 per group; duration not given in the abstract. Read: abstract
Nakagawa 2003 Cytotoxic and xenoestrogenic effects via biotransformation of trans-anethole on isolated rat hepatocytes and cultured MCF-7 human breast cancer cells. Biochem Pharmacol · PMID 12818366 · DOI	Laboratory study (rat liver cells and human breast cancer cells) in-vitro	Isolated rat hepatocytes and cultured MCF-7 human breast cancer cells	trans-Anethole and its metabolites isolated compound 0.25 to 2.0 mM (liver cells); 1e-9 to 1e-5 M (MCF-7) Hours · vs Untreated	Anethole itself did not affect MCF-7 growth, but its breakdown product 4-hydroxy-1-propenylbenzene bound to the oestrogen receptor alpha and made MCF-7 cells grow at low concentrations; at higher concentrations it was toxic. Oestrogen-receptor displacement IC50 about 1e-5 M for the metabolite Methods, limits and funding Outcomes: Cell death; binding to oestrogen receptor; cell growth Limitations: Cells in a dish; the metabolite level in people after normal use is not known. Abstract only. Read: abstract
Namavar Jahromi 2003 Comparison of fennel and mefenamic acid for the treatment of primary dysmenorrhea. Int J Gynaecol Obstet · PMID 12566188 · DOI	Cohort comparison in the same women (three cycles, not randomised)	30 Women aged 15 to 24 with moderate to severe primary dysmenorrhoea, Iran	Sweet fennel fruit essence, 2% (Foeniculum vulgare var. dulce) fruit/seed (essence) 25 drops every 4 hours from the start of the period One cycle (versus a no-treatment cycle and a mefenamic acid cycle) · vs Mefenamic acid 250 mg every 6 hours; a no-medicine control cycle	Both fennel and mefenamic acid reduced pain compared with the control cycle (P<0.001). Mefenamic acid was stronger on days 2 and 3 (P<0.05). Five women (16.6%) dropped out because of fennel odour; one reported mildly increased menstrual flow. Both better than no treatment; mefenamic acid stronger on days 2-3 Methods, limits and funding Outcomes: Pain on a 10-point scale Limitations: Each woman went through the cycles in a fixed order, so order and expectation effects are possible; not blinded or randomised; small. Read: abstract
Negi 2026 Efficacy of ginger and fennel in relieving primary dysmenorrhea: A triple-blind crossover controlled trial. J Educ Health Promot · PMID 42829743 · DOI	Crossover trial (triple blind, placebo controlled)	384 Women aged 18 to 26 with primary dysmenorrhoea, Dehradun, India	Ginger (500 mg), fennel (480 mg) or placebo capsules fruit/seed (fennel) Every 8 hours for the first 3 days of the period 3 cycles per treatment with washouts · vs Placebo	Pain fell from 6.14 to 3.28 with ginger, to 4.61 with fennel, and 6.24 (little change) with placebo. Ginger was strongest. Fennel pain score about 4.61 versus placebo about 6.24 after treatment (starting level not given for fennel in the abstract) Methods, limits and funding Outcomes: Pain severity (visual scale), McGill questionnaire, pain duration Limitations: Starting score for the fennel period is not given. Abstract only. Funding and conflicts: Authors declared no conflict of interest Read: abstract
Ning 2017 Study on inter-ethnic human differences in bioactivation and detoxification of estragole using physiologically based kinetic modeling. Arch Toxicol · PMID 28357488 · DOI	Computer modelling study in-vitro	Liver fraction data from Chinese and Caucasian donors	Estragole (modelled dietary intake) isolated compound Realistic dietary levels	About 0.02% of the dose was converted to the ultimate carcinogenic metabolite in Chinese and 0.09% in Caucasian subjects (a 4.5-fold difference), with similar detoxification. 0.02% versus 0.09% Methods, limits and funding Outcomes: Share of estragole converted to the cancer-causing metabolite Limitations: Model based on liver fractions. Abstract only. Funding and conflicts: Authors declared no conflict of interest Read: abstract
Okdemir 2014 Premature thelarche related to fennel tea consumption? J Pediatr Endocrinol Metab · PMID 24030028 · DOI	Case report	1 A 12-month-old girl in Turkey with breast development (premature thelarche)	Fennel tea, two to three teaspoons a day for about 6 months 2 to 3 teaspoons a day About 6 months	Breast development regressed gradually and was normal by the end of one year after the tea was stopped. The authors suggest anethole as a plant oestrogen-like compound. Single case Methods, limits and funding Outcomes: Breast development after stopping fennel tea Limitations: One case: shows a possible link, cannot show cause or how common. Abstract only. Read: abstract
Paini 2012 In vivo validation of DNA adduct formation by estragole in rats predicted by physiologically based biodynamic modelling. Mutagenesis · PMID 22844077 · DOI	Animal study (rats) animal	60 Male Sprague Dawley rats, 10 per group	Estragole single oral doses 5 to 300 mg/kg isolated compound 5, 30, 75, 150, 300 mg/kg 48 hours · vs Vehicle	DNA adducts rose with dose and were highest in the liver, with lower levels in lung and kidney. A computer model predicted values within an order of magnitude. Dose-dependent liver DNA adducts Methods, limits and funding Outcomes: DNA adducts in liver, kidney and lung Limitations: Single doses far above human exposure. Abstract only. Read: abstract
Pattanittum 2016 Dietary supplements for dysmenorrhoea. Cochrane Database Syst Rev · PMID 27000311 · DOI	Systematic review and meta analysis (Cochrane)	3101 Women with moderate or severe primary dysmenorrhoea; 27 randomised trials of 12 herbs and 5 non-herbal supplements, mostly students in Iran	Dietary supplements including fennel fruit/seed (fennel) Various Various · vs Placebo, no treatment, other supplements, NSAIDs	All evidence was low or very low quality. For fennel versus placebo or no treatment, one trial of 43 women found no consistent benefit (MD -0.34 points, 95% CI -0.74 to 0.06). Ginger, fenugreek, valerian and others had limited evidence of benefit. Few trials reported adverse effects. Fennel MD -0.34 points (1 trial, 43 women) (-0.74 to 0.06) Methods, limits and funding Outcomes: Pain intensity (0-10 scale) and adverse effects Limitations: Cochrane counted only the fennel trial that met its criteria; other fennel trials were in separate comparisons. Abstract only; search to March 2015. Read: abstract
Pellicano 2014 Benefit of supplements in functional dyspepsia after treatment of Helicobacter pylori. Minerva Gastroenterol Dietol · PMID 25384804	Open non randomised comparative study	91 Adults with functional dyspepsia after treatment for Helicobacter pylori, Italy	Perdiges food supplement: sodium alginate, calcium carbonate, pineapple, papaya, ginger, alpha-galactosidase AND fennel. A MULTI-INGREDIENT COMBINATION. Not given in the abstract 30 days · vs No supplement	All 55 treated people (100%) and 31 of 36 untreated (86.1%) stayed off proton-pump inhibitors (P=0.008). Well-being score improved by 1.78 points with the supplement and worsened by 0.08 without (P<0.0001). Score +1.78 versus -0.08 Methods, limits and funding Outcomes: Staying off acid-reducing drugs (PPIs); well-being score on a visual scale Limitations: Open, not randomised or blinded. Seven active ingredients, so fennel cannot be singled out. Waiting period before a breath test, not a long-term trial. Abstract only. Read: abstract
Perry 2011 Nutritional supplements and other complementary medicines for infantile colic: a systematic review. Pediatrics · PMID 21444591 · DOI	Systematic review	Infants with colic; 15 randomised trials of nutritional supplements and other complementary medicines	Several complementary medicines, including fennel extract, mixed herbal tea and sugar solutions various Various Various · vs Placebo in 13 of 15 trials	Eleven of 15 trials favoured the complementary medicine, but none was free of flaws and most treatments had no independent repeat trial. The authors say encouraging results exist for fennel extract, mixed herbal tea and sugar solutions, but the idea that any of these is effective is not currently supported. Not pooled (narrative) Methods, limits and funding Outcomes: Crying time and related colic outcomes Limitations: Search ended February 2010. Eight of 15 trials were of good quality by Jadad score. Only the abstract was read. Read: abstract
Perry 2019 An overview of systematic reviews of complementary and alternative therapies for infantile colic. Syst Rev · PMID 31711532 · DOI	Overview of systematic reviews	Infants up to 1 year with colic; 16 systematic reviews of complementary therapies	Complementary therapies including probiotics, fennel extract, spinal manipulation, acupuncture, soy various Various Various · vs Various	Probiotics, fennel extract and spinal manipulation show promise, with concerns remaining. Most of the 16 reviews had high or unclear risk of bias and low confidence in findings. Larger, better trials are needed. Not pooled Methods, limits and funding Outcomes: Review quality (AMSTAR-2, ROBIS) and conclusions about colic Limitations: Overview of reviews, not of trials. Search to September 2018. Only the abstract was read. One author (Perry) wrote one of the included reviews. Funding and conflicts: One author wrote an included review; others declared none (as stated in the record) Read: abstract
Picon 2010 Randomized clinical trial of a phytotherapic compound containing Pimpinella anisum, Foeniculum vulgare, Sambucus nigra, and Cassia augustifolia for chronic constipation. BMC Complement Altern Med · PMID 20433751 · DOI	Randomized crossover trial (single blind, placebo controlled)	20 Adults with chronic constipation, Brazil	Tea of a compound of anise (Pimpinella anisum), fennel (Foeniculum vulgare), elderberry (Sambucus nigra) and SENNA (Cassia angustifolia). A COMBINATION that includes a stimulant laxative. mixed Not given in the abstract 5 days per treatment with a 9-day washout · vs Placebo	Average transit time was 15.7 hours on the compound and 42.3 hours on placebo (P<0.001). Daily bowel movements rose. Quality of life did not change. Serum potassium fell slightly during active treatment. Transit time 15.7 h versus 42.3 h (95% CI 11.1 to 20.2 (active) and 33.5 to 51.1 (placebo)) Methods, limits and funding Outcomes: Colonic transit time measured by X-ray Limitations: Only 20 people and 5 days. Senna is a stimulant laxative, so the result says little about fennel. Slight fall in potassium. Abstract only. Registration: ClinicalTrials.gov NCT00872430 Read: abstract
Portincasa 2016 Curcumin and Fennel Essential Oil Improve Symptoms and Quality of Life in Patients with Irritable Bowel Syndrome. J Gastrointestin Liver Dis · PMID 27308645 · DOI	Randomized controlled trial	121 Adults with mild-to-moderate irritable bowel syndrome (IBS), Italy	Curcumin plus fennel essential oil capsules (CU-FEO). A COMBINATION product with turmeric extract, so the effect cannot be put down to fennel alone. fruit/seed (essential oil) 2 capsules twice a day 30 days · vs Placebo	The average relative fall in IBS-SSS was 50.05% with CU-FEO and 26.12% with placebo (P<0.001). 25.9% were symptom-free on CU-FEO versus 6.8% on placebo (P=0.005). All quality-of-life areas improved more on CU-FEO. Relative IBS-SSS fall 50.05 +/- 28.85% versus 26.12 +/- 30.62% Methods, limits and funding Outcomes: Change in IBS symptom severity score (IBS-SSS); IBS quality of life Limitations: Abstract only. Curcumin and fennel oil were given together, so fennel alone was not tested. 30 days only. Placebo group also improved by about a quarter. Funding not stated in the abstract (two authors list a company affiliation; the record gives no detail). Read: abstract
Rabsch 2005 Molecular epidemiology of Salmonella enterica serovar Agona: characterization of a diffuse outbreak caused by aniseed-fennel-caraway infusion. Epidemiol Infect · PMID 16181503 · DOI	Laboratory/epidemiological outbreak investigation	165 Salmonella Agona isolates from infants with gastroenteritis in Germany, plus aniseed and tea samples	Aniseed-fennel-caraway infusion in tea bags; untreated aniseed imported from Turkey fruit/seed (tea bag) 2002-2003 outbreak	Clonally identical Salmonella Agona was found in 36 isolates from infants with gastroenteritis, in an untreated batch of aniseed from Turkey and in a fennel-aniseed-caraway infusion in tea bags, pointing to the tea as a source of infection. Matching bacterial type in infants, aniseed and tea bags Methods, limits and funding Outcomes: Typing of bacteria to find the source Limitations: The tea contained fennel, aniseed and caraway; the abstract points to aniseed as the likely carrier. Shows contamination of one product batch, not a general problem. Abstract only. Read: abstract
Raffo 2011 Quantification of estragole in fennel herbal teas: implications on the assessment of dietary exposure to estragole. Food Chem Toxicol · PMID 21094197 · DOI	Chemical analysis and exposure assessment in-vitro	Commercial fennel herbal teas (tea bags, instant, loose seed)	Fennel herbal teas fruit/seed (tea) Three portions a day (model)	Estragole ranged from 241 to 2,058 micrograms per litre in tea bags, 9 to 912 in diluted instant teas and 251 to 1,718 in teas from loose seeds. Adult exposure up to 10 micrograms per kg a day; infants up to 51 (tea bags) and 23 (instant teas) micrograms per kg a day. Some instant teas designed for infants had relatively high levels. Infant exposure up to 51 micrograms per kg per day Methods, limits and funding Outcomes: Estragole concentration and dietary exposure Limitations: Exposure model. Abstract only. Read: abstract
Rafieian 2024 Exploring fennel (Foeniculum vulgare): Composition, functional properties, potential health benefits, and safety. Crit Rev Food Sci Nutr · PMID 36803269 · DOI	Narrative review	Fennel composition, pharmacology and safety literature	Fennel (Foeniculum vulgare) whole plant	The review collects lab and animal studies showing antibacterial, antioxidant, anti-inflammatory and other effects and says fennel has been shown to be effective in infant colic, dysmenorrhoea, polycystic ovary syndrome and milk production, and notes that gaps remain. Not applicable Methods, limits and funding Outcomes: Overview Limitations: Narrative review; its efficacy statements are stronger than the trial evidence in this profile supports. Abstract only. Read: abstract
Rahimikian 2017 Effect of Foeniculum vulgare Mill. (fennel) on menopausal symptoms in postmenopausal women: a randomized, triple-blind, placebo-controlled trial. Menopause · PMID 28509813 · DOI	Randomized controlled trial (triple blind, placebo controlled)	90 Postmenopausal women aged 45 to 60, Tehran	Fennel soft capsules (100 mg fennel) fruit/seed Two capsules a day 8 weeks plus 2 weeks follow-up · vs Placebo	MRS fell in the fennel group at 4, 8 and 10 weeks and not in the placebo group (P<0.001 between groups). Authors say no serious side effects. Between-group P<0.001 at 4, 8, 10 weeks (values not in the abstract) Methods, limits and funding Outcomes: Menopause Rating Scale (MRS) Limitations: Single-country trial; funding not stated; abstract only. A later Iranian trial (Ghazanfarpour 2018) found no difference from placebo. Read: abstract
Saghafi 2017 The Effect of Foeniculum Vulgare (Fennel) on Body Composition in Postmenopausal Women with Excess Weight: A Double-blind Randomized Placebo-controlled Trial. J Menopausal Med · PMID 29354616 · DOI	Secondary analysis of a randomized controlled trial	47 Overweight postmenopausal women, Iran	Fennel fruit/seed Not given in the abstract 12 weeks · vs Placebo	No significant effect. The fennel group had a slight, non-significant rise in weight and fat distribution. No significant between-group difference Methods, limits and funding Outcomes: Body weight, BMI, waist and hip, fat distribution Limitations: Secondary analysis; small; abstract only. Funding and conflicts: Fennel capsules supplied by Barij Essence Pharmaceutical Company; authors state the company did not shape the research Read: abstract
Savino 2005 A randomized double-blind placebo-controlled trial of a standardized extract of Matricariae recutita, Foeniculum vulgare and Melissa officinalis (ColiMil) in the treatment of breastfed colicky infants. Phytother Res · PMID 16041731 · DOI	Randomized controlled trial	93 Breastfed infants with colic (Wessel criteria), Turin, Italy; 88 finished	ColiMil: standardised extract of chamomile (Matricaria recutita), fennel (Foeniculum vulgare) and lemon balm (Melissa officinalis). A COMBINATION product, so the effect cannot be put down to fennel alone. Twice a day (amount not given in the abstract) 1 week · vs Placebo	Average crying time fell from 201.2 to 76.9 minutes a day with the extract and from 198.7 to 169.9 on placebo (P<0.005). Crying time fell in 85.4% on the extract versus 48.9% on placebo. No side effects reported. About 124 minutes a day less crying with the extract versus about 29 minutes with placebo (own subtraction from the reported means) Methods, limits and funding Outcomes: Daily crying time and side effects Limitations: Abstract only. Three-herb combination. One week only. 5 of 93 infants did not finish. Funding not stated in the abstract. Read: abstract
Shahrahmani 2021 Effect of fennel on primary dysmenorrhea: a systematic review and meta-analysis. J Complement Integr Med · PMID 34187122 · DOI	Systematic review and meta analysis	Women with primary dysmenorrhoea; 12 studies in the meta-analysis (Jadad quality scoring)	Foeniculum vulgare (fennel) versus placebo and versus mefenamic acid fruit/seed Various Various · vs Placebo; mefenamic acid	Fennel reduced pain versus placebo (SMD -0.632, 95% CI -0.827 to -0.436; 7 articles, I2 0%). Fennel and mefenamic acid did not differ (SMD -0.214, 95% CI -0.446 to 0.017; 6 trials). Versus placebo SMD -0.632; versus mefenamic acid SMD -0.214 (-0.827 to -0.436; -0.446 to 0.017) Methods, limits and funding Outcomes: Pain intensity Limitations: Search to January 2019; small trials; quality rated with Jadad scale only. Abstract only. The authors recommend fennel strongly, which goes further than the data. Read: abstract
Shayan 2026 Comparison of the Effects of Propolis and Fennelin Capsules on Premenstrual Syndrome in Students: A Randomized Clinical Trial. Rev Recent Clin Trials · PMID 41510731 · DOI	Randomized controlled trial (double blind)	90 Students with premenstrual syndrome, Hamadan, Iran	Fennelin capsules (30 mg fennel extract), propolis 500 mg, or placebo fruit/seed (extract) Per capsule 30 mg extract 2 menstrual cycles · vs Placebo	Propolis and fennelin reduced PMS severity by 78.9% and 79.3% (P=0.016); no significant change with placebo. No side effects reported. Severity fall 79.3% (fennelin) Methods, limits and funding Outcomes: PMS symptom severity and frequency Limitations: Small sample, only two cycles, short follow-up, per the authors. Abstract only. Product is a branded extract; funding not stated. Registration: IRCT20120215009014N525 Read: abstract
Skalli 2011 Epileptic seizure induced by fennel essential oil. Epileptic Disord · PMID 21865126 · DOI	Case report	1 A 38-year-old woman with well-controlled epilepsy	Cakes containing an unknown amount of fennel essential oil fruit/seed (essential oil, eaten) Unknown Single exposure	She had a generalised tonic-clonic seizure and was unconscious for 45 minutes after eating the cakes. The authors suggest people with epilepsy should avoid fennel essential oil. Single case Methods, limits and funding Outcomes: Seizure Limitations: One case with unknown amount; shows a possible link only. Abstract only. Read: abstract
Thaliyil Poduval 2026 Efficacy of herbaceous Apiaceae plants in primary dysmenorrhea: A systematic review and meta-analysis of RCTs. Ann Pharm Fr · PMID 41653970 · DOI	Systematic review and meta analysis	Women with primary dysmenorrhoea; 14 randomised trials of herbs from the carrot family (fennel, anise, dill, cumin)	Herbs from the Apiaceae family including fennel seed fruit/seed Various Various · vs Placebo or standard treatments (mefenamic acid, ibuprofen)	Seven trials against standard treatments pooled to a statistically significant effect with low heterogeneity, and a fennel and dill seed subgroup against mefenamic acid or ibuprofen also favoured the herbs. Risk of bias had concerns in trials against standard treatments (deviations from intervention, selective reporting). Statistically significant (value not given in the abstract) Methods, limits and funding Outcomes: Pain and safety Limitations: The abstract gives no numbers, and mixes several herbs. Concerns about bias. Abstract only. Registration: PROSPERO CRD42024538888 Read: abstract
Wagner 2019 The Safety of Mother's Milk® Tea: Results of a Randomized Double-Blind, Controlled Study in Fully Breastfeeding Mothers and Their Infants. J Hum Lact · PMID 30005170 · DOI	Randomized controlled trial (double blind, safety study)	60 Exclusively breastfeeding mothers with no milk shortage, and their infants, USA	Mother's Milk herbal tea: bitter fennel, anise and coriander fruits, fenugreek seed and other herbs. A MULTI-HERB BLEND. fruit/seed (blend) Daily tea as recorded in diaries (amount not given in the abstract) 30 days; follow-up to infant age 12 months · vs Lemon verbena leaf tea (placebo)	No adverse effects attributable to the tea were reported at any time. No differences between tea and placebo in symptoms, quality of life, infant growth or satisfaction. No difference in infant growth or adverse symptoms (P>0.05) Methods, limits and funding Outcomes: Maternal and infant adverse effects, infant growth Limitations: Mothers had no milk shortage, so the trial says nothing about milk supply. Blend of many herbs. Small. Adverse effects self-reported. Abstract only. The tea is a commercial product; funding not stated in the abstract. Read: abstract
Xu 2020 Efficacy of herbal medicine (cinnamon/fennel/ginger) for primary dysmenorrhea: a systematic review and meta-analysis of randomized controlled trials. J Int Med Res · PMID 32603204 · DOI	Systematic review and meta analysis	647 Women with primary dysmenorrhoea; 9 studies of cinnamon, fennel or ginger	Cinnamon, fennel or ginger versus placebo fruit/seed (fennel) Various Various · vs Placebo	Fennel versus placebo: WMD 0.528 (95% CI 0.119 to 6.829) reduction in pain intensity; ginger and cinnamon larger. Only cinnamon shortened pain duration. Fennel vs placebo WMD 0.528 (0.119 to 6.829 (as printed; very wide)) Methods, limits and funding Outcomes: Pain intensity and duration Limitations: The fennel confidence interval is very wide and printed oddly (0.119 to 6.829). Mixed herbs in one analysis. Abstract only. Read: abstract
Yancu 2019 Evaluating the effects on steroidogenesis of estragole and trans-anethole in a feto-placental co-culture model. Mol Cell Endocrinol · PMID 31536780 · DOI	Laboratory study (human cell co culture) in-vitro	Human fetal-like adrenal cells (H295R) and placenta-like cells (BeWo) in co-culture	Estragole and trans-anethole, 2.5, 5.2 and 25 micromolar fruit/seed (isolated compounds) 2.5 to 25 micromolar 24 hours · vs Untreated cells	Both compounds raised oestradiol, oestrone, DHEA, androstenedione, progesterone and oestriol in the cell mix and changed several steroid-making enzymes. The authors identify a pathway (cyclic AMP) involved. Significant increases in six hormones Methods, limits and funding Outcomes: Hormone levels and enzyme gene activity Limitations: Cells in a dish, not pregnant women. Concentrations not matched to human exposure. Abstract only. Read: abstract
Yaralizadeh 2016 Effect of Foeniculum vulgare (fennel) vaginal cream on vaginal atrophy in postmenopausal women: A double-blind randomized placebo-controlled trial. Maturitas · PMID 26617271 · DOI	Randomized controlled trial (double blind, placebo controlled)	60 Postmenopausal women aged 45 to 65, Ahvaz, Iran	Fennel 5% vaginal cream fruit/seed (cream) 5 g a day, once daily 8 weeks · vs Placebo cream	Superficial cells rose to 76.1 +/- 15.3 versus 11.8 +/- 8 (P<0.001); vaginal pH fell in all of the fennel group versus 7.4% of placebo; all fennel women reached an index of 65 to 100. Authors say no side effects. Superficial cells 76.1 vs 11.8; pH improved 100% vs 7.4% Methods, limits and funding Outcomes: Vaginal pH and Maturation Vaginal Index; atrophy symptoms Limitations: Applied in the vagina, so oral results do not apply. Small (60). Very large differences from a single small trial, which should be treated cautiously. Abstract only. Read: abstract
Zhang 2018 Fennel main constituent, trans‑anethole treatment against LPS‑induced acute lung injury by regulation of Th17/Treg function. Mol Med Rep · PMID 29901094 · DOI	Animal study (mice) animal	Mice with lipopolysaccharide-induced acute lung injury	trans-Anethole, 36.4, 72.8 or 145.6 mg/kg fruit/seed (isolated compound) 36.4 to 145.6 mg/kg per day 7 days · vs Dexamethasone; untreated	Anethole reduced lung tissue damage and inflammatory cells and shifted immune cells toward the regulatory type. Not given as numbers in the abstract Methods, limits and funding Outcomes: Lung damage, inflammatory cells, IL-17 and IL-10, Th17/Treg cells Limitations: Mouse injury model; isolated compound at high doses; abstract only. Read: abstract
Zhang 2022 Traditional Chinese Nursing Using Fennel With Coarse Salt for Ironing and Umbilical Moxibustion for Epigastric Pain With Spleen-stomach Vacuity Cold. Altern Ther Health Med · PMID 35951072	Randomized controlled trial	96 Patients with chronic upper-stomach pain of the Chinese-medicine "spleen-stomach vacuity cold" pattern (equivalent to chronic atrophic gastritis), Guangxi, China	Traditional Chinese nursing: fennel mixed with coarse salt, heated and pressed on the skin ("ironing"), PLUS moxibustion at the navel. Fennel was NOT swallowed. fruit/seed (external) Not given in the abstract Not given in the abstract · vs Routine nursing care	Stomach pain fell more, and quality of life and satisfaction were higher, in the treatment group (P<0.05). P<0.05 (values not given in the abstract) Methods, limits and funding Outcomes: Chinese-medicine symptom score, quality of life (SF-36), satisfaction Limitations: Two treatments given together (fennel-salt heat plus moxibustion), compared only with routine care, so the fennel part cannot be separated. External use. Abstract only. Read: abstract
Zhu 1999 Effect of oral administration of fennel (Foeniculum vulgare) on ciprofloxacin absorption and disposition in the rat. J Pharm Pharmacol · PMID 10678493 · DOI	Animal pharmacokinetic study (rats) animal	10 Male Sprague-Dawley rats (5 per group)	Ciprofloxacin 20 mg/kg by mouth with or without aqueous fennel extract (2 g herb/kg) fruit/seed (aqueous extract) 2 g herb per kg 6-hour and 24-hour sampling · vs Ciprofloxacin alone	With fennel, ciprofloxacin peak level fell 83%, AUC fell 48% and urinary recovery fell 43% (relative bioavailability about 0.52). Distribution volume and half-life rose. The authors think metal ions in the extract bind the antibiotic. Peak -83%, AUC -48%, urinary recovery -43% (Not given) Methods, limits and funding Outcomes: Blood levels of ciprofloxacin Limitations: Five rats per group; rat dose of 2 g herb/kg is high in human terms; shows a chelation-type effect, not proof in people. Abstract only. Read: abstract
s-ema-estragole-statement-2014-draft Public statement on the use of herbal medicinal products containing estragole, DRAFT Revision 1 (24 November 2014), EMA/HMPC/137212/2005 Rev 1 (European Medicines Agency, HMPC) · Source	Regulatory statement n/a			Methods, limits and funding Read: full-text
s-ema-hmpc-fennel-bitter EU herbal monograph on Foeniculum vulgare Miller subsp. vulgare var. vulgare, fructus (bitter fennel fruit), Final Revision 1, EMA/HMPC/372841/2016, adopted 31 January 2024 (European Medicines Agency, HMPC) · Source	Regulatory monograph n/a			Methods, limits and funding Read: full-text
s-ema-hmpc-fennel-sweet EU herbal monograph on Foeniculum vulgare Miller subsp. vulgare var. dulce (Mill.) Batt. & Trab., fructus (sweet fennel fruit), Final Revision 1, EMEA/HMPC/372839/2016, adopted 31 January 2024 (European Medicines Agency, HMPC) · Source	Regulatory monograph n/a			Methods, limits and funding Read: full-text
s-gbif-foeniculum-vulgare GBIF Backbone Taxonomy: Foeniculum vulgare Mill. (usageKey 3034922) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-hmpc-meeting-report-2022-07 HMPC meeting report, 18-20 July 2022 (EMA/HMPC/658338/2022): draft revised fennel fruit monographs and draft public statement on bitter fennel oil · Source	Committee report n/a			Methods, limits and funding Read: full-text
s-lactmed-fennel Fennel. Drugs and Lactation Database (LactMed), National Institute of Child Health and Human Development (entry dated 2026-10-15 in the PubMed record) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-ncbi-taxonomy-fennel NCBI Taxonomy: fennel (taxid 2849586, listed as Anethum foeniculum) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-usda-fdc-169385 USDA FoodData Central: Fennel, bulb, raw (SR Legacy, FDC ID 169385, NDB 11957, published 2019-04-01) · Source	Reference database n/a			Methods, limits and funding Read: full-text
van den Berg 2014 Chemical analysis of estragole in fennel based teas and associated safety assessment using the Margin of Exposure (MOE) approach. Food Chem Toxicol · PMID 24384409 · DOI	Chemical analysis and risk assessment in-vitro	Dry fennel preparations and infusions; fennel tea intake of 1 to 3 cups	Fennel-based teas fruit/seed (tea) 1 to 3 cups a day (model) Lifetime and short-term models	Estragole was 0.15 to 13.3 mg per gram of dry fennel; infusions held far less (0.4 to 133.4 micrograms per 25 mL from 1 g). Whole fruit gave about three times less than fine cut material. For adults MOEs pointed to low priority for risk management, especially for one cup a day. For children MOEs were mostly below 10,000, indicating priority for risk management, but if use is limited to 1-2 weeks MOEs rise about a thousand-fold. MOE below 10,000 for children with continued use Methods, limits and funding Outcomes: Estragole content and margin of exposure (MOE) compared with rodent tumour data Limitations: A calculation from rodent data. Brands tested are from one time and market. Abstract only. Read: abstract
Ștefănescu 2023 Fennel Essential Oil as a Complementary Therapy in the Management of Diabetes. Pharmaceutics · PMID 38139998 · DOI	Animal study (rats) with chemical analysis animal	Diabetic rats	Fennel essential oil, topical or oral (64.6% trans-anethole, 24.5% fenchone) fruit/seed (essential oil) Not given in the abstract 4 weeks · vs Untreated diabetic rats	Blood sugar fell significantly in diabetic rats with no difference between skin and oral use. P<=0.05 (numbers not in abstract) Methods, limits and funding Outcomes: Blood sugar; ex vivo cataract model Limitations: Rat study only; abstract only. Funding and conflicts: Authors declared no conflict of interest Read: abstract

What we do not know yet

What the evidence supports: nothing reaches moderate certainty. Infant colic, IBS (as a curcumin and fennel oil mix), period pain, post-surgery bowel recovery and skin products for hair are low certainty; menopause and weight are mixed.
What is uncertain: most trials are small, short, from a few countries (especially Iran), use different fennel products or mixes with other herbs, and were only read as abstracts. Several 'positive' trials contain senna, aloe or valerian.
What has never been tested: fennel alone for indigestion, IBS or constipation; long-term safety in babies and children; fennel with tamoxifen or other hormone treatments; any human trial for blood sugar or cough; oestrogen-like effects in women using standard fennel tea.
Safety unknowns: the final EU estragole statement and the fate of the bitter fennel oil monograph were not checked; case reports (infant breast development, seizure, newborn toxicity) cannot show how common these are.
Reviews of colic treatments disagree on how strong the fennel evidence is, and no fennel-specific GRADE rating was found.

How new research is added

New studies are found by a saved PubMed search and are placed in a review queue. A person reads each one before it changes any evidence rating or safety wording.

Lab markers

What changed in blood or saliva tests during trials. A changed number is not the same as feeling or being healthier, and we give no "normal ranges".

Hormonal 1

↕

Blood oestradiol

Mixed results in trials

The main oestrogen hormone in the blood (pg/mL or similar).

Mixed findings

Results and what it means

Why it was measured

Checks whether fennel acts like oestrogen in the body.

Statistical vs. clinical meaning

The first trial does not show a rise; the second cannot be interpreted from the abstract.

Safety implication

Relevant to women with hormone-sensitive conditions; no clear signal of an oestrogen rise.

Study	Result	People	Product
²⁸	Fell in both groups: 60.4 to 52.6 with fennel and 55.1 to 39.9 with control; difference between groups not significant	80 postmenopausal women	Fennel seed powder 2 g/day, 8 weeks
²⁹	Changed significantly versus placebo (P<0.001); direction not stated in the abstract	125 postmenopausal women	Fennel versus evening primrose oil, 8 weeks

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Other 17

▼

Crying time in colicky infants (minutes per day)

Lowered in trials

How long a baby cries or fusses each day, usually written in a parent diary. Colic is often defined as crying for more than 3 hours a day, 3 days a week, in a healthy baby.

Low certainty

Results and what it means

Why it was measured

Main outcome of colic trials.

Statistical vs. clinical meaning

A drop of an hour or more a day would matter to families, but the intervals are wide and parents measured it. Colic also fades by itself.

Safety implication

No harm was reported, but infant safety data are thin.

Study	Result	People	Product
⁷⁹	Crying fell from 201.2 to 76.9 min/day with the three-herb extract versus 198.7 to 169.9 min/day with placebo (P<0.005)	88 breastfed colicky infants finishing	Chamomile + fennel + lemon balm extract, 1 week
³⁷	Pooled difference -72.1 min/day (95% CI -126.4 to -17.7) across 3 fennel-containing trials	Breastfed or mixed-fed colicky infants	Fennel-containing preparations (mixed products)

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▲

Share of infants whose colic resolved (crying under 9 hours a week)

Raised in trials

The proportion of babies no longer meeting the Wessel criteria (a classic 'rule of threes' definition of colic).

Low certainty

Results and what it means

Why it was measured

Alexandrovich trial's main outcome.

Statistical vs. clinical meaning

Large difference but from one unreplicated trial of 121 analysed infants.

Safety implication

No side effects reported in the trial.

Study	Result	People	Product
⁶	Colic eliminated in 65% (40/62) versus 23.7% (14/59) on placebo (P<0.01)	125 infants aged 2 to 12 weeks	Fennel seed oil emulsion

⁶

▼

IBS symptom severity score (IBS-SSS)

Lowered in trials

A questionnaire (0 to 500) covering pain, bloating, bowel habit and life interference. Lower is better.

Low certainty

Results and what it means

Why it was measured

Main outcome of the curcumin plus fennel oil IBS trial.

Statistical vs. clinical meaning

Clearly better than placebo in the trial but placebo itself helped a lot, and the product has two active ingredients.

Safety implication

Well tolerated in the trial.

Study	Result	People	Product
⁷³	Relative fall 50.05 +/- 28.85% versus 26.12 +/- 30.62% with placebo (P<0.001); symptom-free 25.9% versus 6.8%	121 adults with mild to moderate IBS	Curcumin + fennel essential oil capsules, 30 days

^{73 20}

▼

Colonic transit time (hours)

Lowered in trials

How long markers take to pass through the large bowel, measured by X-ray. A shorter time suggests faster movement.

Very low certainty

Results and what it means

Why it was measured

Objective gut speed measure in the Brazilian constipation trial.

Statistical vs. clinical meaning

Large, but the tea contains senna, a stimulant laxative, so fennel's part is unknown.

Safety implication

A small fall in serum potassium was seen during active treatment.

Study	Result	People	Product
⁷²	15.7 h (95% CI 11.1 to 20.2) on the compound versus 42.3 h (33.5 to 51.1) on placebo (P<0.001)	20 adults with chronic constipation	Anise + fennel + elderberry + senna tea, 5 days

⁷²

▼

Time to first passing of gas after surgery (hours)

Lowered in trials

A common sign that the bowel is working again after an operation.

Low certainty

Results and what it means

Why it was measured

Main recovery marker in post-surgery trials.

Statistical vs. clinical meaning

An 11-hour shorter wait is useful for recovery planning but is a hospital-process measure.

Safety implication

None reported.

Study	Result	People	Product
⁵⁰	53.1 +/- 11.3 h with fennel tea versus 64.2 +/- 13.6 h with water (P<0.001)	159 women after gynaecological cancer surgery	Fennel fruit tea, twice a day
¹⁸	Time to first flatus shorter with heated fennel pack than heated rice husk (P<0.05); exact values not in abstract	381 patients after major abdominal surgery	Heated fennel pack on the abdomen

^{50 18}

▼

Gas (flatulence) score on a visual scale

Lowered in trials

Patients rate how gassy they feel on a line from none to worst.

Very low certainty

Results and what it means

Why it was measured

Main outcome of the post-caesarean trial.

Statistical vs. clinical meaning

Both reduced gas; no placebo, so the share due to fennel is unknown.

Safety implication

None reported in the abstract.

Study	Result	People	Product
⁴¹	Fell in both fennel and dimethicone groups; no difference between groups (P=0.607)	Women after caesarean section	Fennel capsules versus dimethicone

⁴¹

▼

Period pain score (visual scale)

Lowered in trials

Women mark how bad their period pain is on a line from none to worst (0 to 10).

Low certainty

Results and what it means

Why it was measured

Main outcome of dysmenorrhoea trials.

Statistical vs. clinical meaning

Statistical significance is clear in some analyses and absent in Cochrane's single-trial comparison; the size of effect ranges from small to huge, so the real effect is uncertain.

Safety implication

Pain relief did not appear to carry serious side effects in the trials.

Study	Result	People	Product
⁴⁶	SMD -3.27 (95% CI -5.28 to -1.26) versus placebo, I2 98%; SMD 0.07 versus drugs	468 and 502 women in pooled trials	Fennel, various
⁸⁰	SMD -0.632 (95% CI -0.827 to -0.436) versus placebo; SMD -0.214 (-0.446 to 0.017) versus mefenamic acid	Women with primary dysmenorrhoea	Fennel, various
⁶⁸	MD -0.34 points (95% CI -0.74 to 0.06), one trial	43 women	Fennel versus placebo or no treatment
⁶⁴	VAS about 4.61 on fennel versus 6.24 on placebo; ginger 3.28	384 women	Fennel 480 mg every 8 hours

^{46 80 68 64}

▼

PMS symptom score

Lowered in trials

Questionnaire scores for mood and body symptoms before periods (daily record scales).

Very low certainty

Results and what it means

Why it was measured

Main outcome of PMS trials.

Statistical vs. clinical meaning

Positive in all three small trials, but self-rated scores respond strongly to placebo.

Safety implication

One combination trial saw more bleeding.

Study	Result	People	Product
⁸¹	Severity fell 79.3% with fennel extract (P=0.016); no change with placebo	90 students	Fennelin 30 mg extract
¹⁹	64.4 with fennel versus 79.1 with placebo after treatment (P<0.001)	90 students	Fennel extract

^{81 19}

↕

Menopause symptom score (Menopause Rating Scale or Kupperman index)

Mixed results in trials

Questionnaires that add up hot flushes, sleep, mood, joint and vaginal symptoms.

Mixed findings

Results and what it means

Why it was measured

Main outcome of menopause trials.

Statistical vs. clinical meaning

Direction is mostly positive but one null trial and small sizes.

Safety implication

No serious events reported.

Study	Result	People	Product
⁴⁷	SMD -1.32 (95% CI -1.76 to -0.87), two trials	145 women	Fennel versus placebo
⁷⁷	Lower than placebo at 4, 8 and 10 weeks (P<0.001)	90 women	Fennel 100 mg capsules x 2/day
²⁸	Kupperman 30.8 to 19 versus 31.2 to 26.4 (P<0.05)	80 women	Fennel seed powder 2 g/day
³²	No significant difference from placebo except one item	50 women	Oral fennel, 3 months

^{47 77 28 32}

●

Sleep quality score (Pittsburgh Sleep Quality Index)

No clear change in trials

Questionnaire about sleep; higher scores mean worse sleep.

Very low certainty

Results and what it means

Why it was measured

Main outcome of menopause sleep trials.

Statistical vs. clinical meaning

Fennel alone: not different from placebo. The combination with valerian was better, but valerian could explain it.

Safety implication

None.

Study	Result	People	Product
²	Total score P=0.439 versus placebo; sleep duration tendency P=0.059	50 menopausal women	Fennel, 12 weeks
⁴⁰	Lower than control at 2 months (P=0.030)	76 postmenopausal women	Fennel-valerian extract 500 mg x 2/day, 8 weeks

^{2 40}

●

Cholesterol and triglycerides

No clear change in trials

Blood fats: total cholesterol, LDL ('bad'), HDL ('good') and triglycerides.

Low certainty

Results and what it means

Why it was measured

Heart health marker.

Statistical vs. clinical meaning

No difference from placebo in the one fennel-alone trial.

Safety implication

None.

Study	Result	People	Product
³	Triglycerides P=0.679, total cholesterol P=0.103, LDL P=0.146, HDL P=0.266 versus placebo	60 postmenopausal women	Fennel, 3 months

^{3 44}

↕

Vaginal cell maturation and pH

Mixed results in trials

A smear count of surface versus deeper cells that rises when the vaginal lining is healthy (oestrogen-sensitive), plus acidity (pH).

Very low certainty

Results and what it means

Why it was measured

Marker of vaginal atrophy.

Statistical vs. clinical meaning

Oral: null. Cream: large, but a single small trial.

Safety implication

The cream's oestrogen-like effect on the womb lining was not assessed.

Study	Result	People	Product
³¹	No difference from placebo for any cell type (P=0.19 to 0.82)	60 postmenopausal women	Oral fennel, 3 months
⁸⁷	Superficial cells 76.1 +/- 15.3 versus 11.8 +/- 8 (P<0.001); pH improved in 100% versus 7.4%	60 postmenopausal women	5% fennel vaginal cream, 8 weeks

^{31 87}

▼

Facial hair diameter or thickness

Lowered in trials

Width of facial hairs under a microscope (microns).

Low certainty

Results and what it means

Why it was measured

Main outcome of hirsutism trials.

Statistical vs. clinical meaning

Both small trials show thinner hair with fennel on the skin.

Safety implication

Itching or irritation in a few users.

Study	Result	People	Product
³⁹	-7.8% (1% cream), -18.3% (2% cream), +0.5% (placebo)	38 women	Fennel extract cream
⁴	97.9 to 75.6 microns with 3% fennel gel (P<0.001, within group)	44 women	Fennel gel 3%, 24 weeks

^{39 4}

↕

Antral follicle count and AMH

Mixed results in trials

Antral follicles are resting egg sacs seen on ultrasound; AMH is a hormone linked to egg reserve.

Very low certainty

Results and what it means

Why it was measured

Fertility reserve markers.

Statistical vs. clinical meaning

Small, opposite-direction changes in two conditions (more follicles in POI, fewer in PCOS), each from one small trial.

Safety implication

Not assessed.

Study	Result	People	Product
¹⁴	AFC +1.6 (95% CI 0.07 to 3.1; P=0.040); AMH no difference (P=0.986)	60 women with occult POI	Fennel extract, 60 days
³⁰	Ovarian follicle numbers lower with fennel versus placebo (P<0.05)	47 women with PCOS	Fennel 46 mg x 2/day, 3 months

^{14 30}

▲

Womb lining (endometrial) thickness

Raised in trials

Thickness of the lining of the womb on ultrasound (mm).

Very low certainty

Results and what it means

Why it was measured

Lining thickness matters for embryo implantation.

Statistical vs. clinical meaning

Statistical difference, but no clear improvement in pregnancy and no placebo.

Safety implication

Possible oestrogen-like effect on the womb lining was not assessed.

Study	Result	People	Product
⁴²	About 1.7 mm thicker with fennel than control (P<0.001)	60 women taking clomiphene	Fennel 60 mg/day

⁴²

▼

WOMAC knee pain and function score

Lowered in trials

A questionnaire for pain, stiffness and function in knee osteoarthritis.

Very low certainty

Results and what it means

Why it was measured

Main outcome of the knee trial.

Statistical vs. clinical meaning

One short trial; numbers not in the abstract.

Safety implication

None reported.

Study	Result	People	Product
⁵	Pain, disability and total score lower than placebo after 2 weeks; stiffness not different	66 women	Sweet fennel seed extract, 2 weeks

⁵

↕

Milk volume and infant weight

Mixed results in trials

Milk volume pumped or weighed, and the baby's weight gain.

Not enough evidence

Results and what it means

Why it was measured

Main outcomes of galactagogue trials.

Statistical vs. clinical meaning

Cochrane cannot say whether fennel has an effect.

Safety implication

See safety file.

Study	Result	People	Product
²⁴	Very uncertain whether fennel or fenugreek improves infant weight; milk volume results could not be pooled (I2 99%)	3,005 mothers across 41 trials	Natural galactagogues including fennel

^{24 84}

Safety

What studies and official sources say about side effects, medicines and who should check first. Each point shows what kind of evidence it comes from.

Main points to know 7

Estragole and anethole: a natural fennel compound that causes liver tumours in rodents, so exposure is kept low and use is kept short. Fennel fruit and its oil contain anethole (the main compound) and a smaller amount of estragole. In rodents, estragole at high doses causes DNA damage and liver tumours. The EU herbal committee calls it a genotoxic carcinogen in rodents and says exposure in the general population should be kept as low as practically achievable. It concluded in 2005 that short-term use by adults at normal tea doses does not pose a significant cancer risk, but asked that exposure of young children, pregnant and breastfeeding women be minimised. For this reason the EU monographs limit use to 2 weeks in adults and set daily estragole limits for pregnancy, breastfeeding and children. Estragole varies enormously between products (0.15 to 13.3 mg per gram of dry fennel), and much less ends up in tea than in oil. Margin-of-exposure studies find a low priority for risk management for adults who drink one cup a day, but not for children if use continues long term. Authoritative guidance ^{92 93 91 99 53 75 21 16 52 22}
Babies and children: the EU does not recommend fennel fruit preparations under 4 years, and limits use at 4 to 12. The 2024 EU monographs on bitter and sweet fennel fruit state that use is not recommended in children under 4 years because of lack of adequate data. For children 4 to 12 years the use is limited to short courses (less than one week) and is not recommended if the daily intake of estragole exceeds 1.0 microgram per kg of body weight, unless a risk assessment justifies it. Use for period spasm under age 12 is not recommended. This is more specific than a blanket ban for all infants and children: the monograph addresses medicinal fruit preparations and does not say that fennel eaten as a food is unsafe. Fennel preparations nonetheless are widely given to colicky babies, and small trials report no side effects. One 12-month-old girl developed breast development that went away after her daily fennel tea was stopped (a single case report), and measured estragole in instant and bagged fennel teas aimed at infants gave estimated infant intakes up to 51 micrograms per kg a day. A parent should ask a paediatrician or pharmacist before giving any fennel product to a baby. Authoritative guidance ^{92 93 66 75 53 99 9 6}
Pregnancy and breastfeeding: the EU says use is not recommended. The EU monographs say safety in pregnancy and breastfeeding has not been established and use is not recommended, because of missing data and the estragole concern. Daily estragole must stay below 0.05 mg per person in pregnancy and breastfeeding. A fennel seed extract given to pregnant mice (days 6 to 15) caused dose-dependent birth defects (EU monograph); reproduction tests have not been done properly. Anethole passes into breast milk. LactMed notes that fennel is generally well tolerated in adults and that a fennel-containing tea used excessively by breastfeeding mothers seemed to cause toxicity in two newborns, and that fennel can cause allergy and photosensitivity. A small trial of a blended fennel tea in breastfeeding mothers found no adverse events (but tested a blend, not fennel alone). Authoritative guidance ^{92 93 96 84}
Allergy: people allergic to carrot-family plants or mugwort pollen should avoid fennel. The EU monographs list hypersensitivity to fennel, to plants of the carrot family (Apiaceae), including aniseed, caraway, celery, coriander and dill, to anethole, or to mugwort pollen (cross-reaction) as reasons not to use fennel fruit. Allergic reactions affecting the skin or breathing may occur; how often is not known. LactMed adds that fennel oil can cause allergic reactions on the skin or in the airways. EFSA classes fennel essential oils as skin and respiratory sensitisers. Authoritative guidance ^{92 93 96 22}
Hormone-sensitive conditions: fennel has weak oestrogen-like activity in the lab, but human data do not show a clear oestrogen rise. Fennel is often described as a 'phytoestrogen' herb. In lab work a breakdown product of anethole bound to the oestrogen receptor and made oestrogen-sensitive breast cancer cells grow, while anethole itself reduced survival of both oestrogen-sensitive and insensitive breast cancer cells at a very high concentration; estragole and anethole raised oestrogen and other steroid hormones in a human placenta-adrenal cell model. In people, an 8-week trial of fennel seed powder in postmenopausal women found oestradiol did not rise with fennel; a second trial reported changes in oestradiol and FSH without giving the direction in the abstract. Fennel brought on bleeding in 73% of women with no periods on a hormonal contraceptive injection (versus 19% on placebo), and two trials noted heavier bleeding. One infant case of early breast development was reported. The EU monographs do not list breast cancer or hormone-sensitive conditions as contraindications, and no study of fennel with tamoxifen or other hormone therapies was found. Women with oestrogen-sensitive cancers or conditions (breast, womb or ovarian cancer, endometriosis, fibroids), those on hormone therapy and those taking contraception should speak to their specialist first. This is precaution based on theory and mixed data, not a proven harm. Laboratory research ^{62 17 86 28 29 55 66 58 63 92}
Fennel essential oil: a seizure case, and the EU proposed withdrawing its monograph on bitter fennel oil. One case report describes a generalised seizure in a woman with epilepsy after she ate cakes containing an unknown amount of fennel essential oil. The authors advise people with epilepsy to avoid fennel essential oil. The EU herbal committee, in July 2022, proposed withdrawing its monograph on bitter fennel oil because of new safety concerns (the final decision was not checked). EFSA classes fennel oils as suspected of causing genetic defects and cancer because of their estragole content and as skin, eye and airway irritants. Essential oils are far more concentrated than tea or the spice. Case report ^{82 95 22}
Medicines: ciprofloxacin absorption fell in rats; the EU lists no reported interactions, but formal studies are almost absent. In rats, an aqueous fennel extract given with ciprofloxacin cut the antibiotic's peak blood level by 83% and its total exposure by 48%, probably because metal ions in the extract bind it. No human study was found. The EU monographs say no interactions have been reported, which reflects little research rather than proven absence. Because fennel affected bleeding in women on a hormonal injection, it could in principle affect hormone treatments. See the interactions list. Animal research ^{90 92 55}

Side effects 10

Effect	How often	Severity and recovery	Evidence
Allergic reactions of the skin or breathing (rash, itch, wheeze) Possible cross-reaction in people allergic to celery, carrot, aniseed, caraway, coriander, dill or mugwort pollen.	Frequency not known (EU monograph)	mild to severe Usually settles after stopping; severe reactions need emergency care	Authoritative guidance ^{92 93 96}
Fennel smell or taste leading to stopping treatment Taken as drops of 2% fruit essence; unusual form.	5 of 30 women (16.6%) stopped fennel essence in one dysmenorrhoea study	mild Stops after stopping	Controlled trial ⁶³
Heavier or earlier menstrual bleeding Bleeding-inducing effect was used as a benefit in the DMPA trial. A concern if you bleed heavily or take blood thinners or hormones.	One of 30 women reported mildly increased flow (Namavar Jahromi 2003); mean flow 21 cc versus 12 cc on placebo in women on DMPA; bleeding volume rose in a fennel-borage PMS trial	mild to moderate Ends after the course	Controlled trial ^{63 55 58}
Mild diarrhoea The fennel-rose formula had milder side effects than the laxative it was compared with.	Reported as mild in the fennel-rose formula group (Azimi 2022); counts not given in the abstract	mild Settles after stopping	Controlled trial ¹²
Skin itch or irritation (gel or cream) Topical fennel only.	8 patients in the hirsutism gel trial reported itching or irritation, 6 of them on fennel gel; the difference was not statistically significant	mild Stops after stopping	Controlled trial ⁴
Sun sensitivity (photosensitivity) Fennel contains small amounts of furocoumarins (psoralen, bergapten, imperatorin) that can sensitise skin to sunlight. LactMed advises avoiding excessive sun or UV while using fennel. Fresh plant juice on skin carries more risk than a swallowed fruit.	Not known; LactMed lists it under adverse reactions, and furocoumarin content in fennel fruit was low (up to 1.22 micrograms a day at the top EU dose)	mild to moderate Fades with avoiding sun	Authoritative guidance ^{96 43}
Premature breast development in a 12-month-old after months of daily fennel tea (single case) Does not prove fennel was the cause.	One case report; no frequency	moderate (distressing; regressed over a year) Regressed over about a year after stopping	Case report ⁶⁶
Seizure after eating a large amount of fennel essential oil (single case) Oil, not tea or seed; woman had epilepsy.	One case report; no frequency	severe Recovered; unconscious for 45 minutes	Case report ⁸²
Toxicity in two breastfed newborns after the mother drank a lot of a herbal tea containing fennel and anise Tea had several herbs. Anethole is the suspected cause according to LactMed.	Two infants (cited in LactMed, individual reports not read)	moderate Not stated in the LactMed text	Case report ⁹⁶
No adverse effects found in several trials Trials were small and short, so they cannot detect rare harm.	No adverse effects attributable to a fennel-containing tea in 60 breastfeeding mothers and infants over a month, with follow-up to 12 months; no side effects reported in colic trials of fennel oil and a three-herb extract	n/a n/a	Controlled trial ^{84 6 79}

Liver

We found no published case series of fennel-induced liver injury in people. LactMed reports elevated liver enzymes in one woman taking Mother's Milk Tea (which contains fennel) and diarrhoea with an enlarged liver in a woman taking fennel, fenugreek and goat's rue together, but neither case points to fennel alone and the original reports were not read. In animals, estragole (a minor part of fennel) damaged the liver at high doses and caused liver tumours in mice. NTP rat and mouse studies found raised liver enzymes and liver weights at 75 mg/kg a day and above, much higher than human intake. ^{96 16 21}

How often. No frequency of liver injury in people could be found. A LiverTox entry for fennel was not read.

Monitoring. No agency monitoring advice was found. Stop and seek care for yellow skin or eyes, dark urine, pale stools or severe tiredness.

This is a safety connection. It is not evidence that Fennel supports liver health.

Medicines and supplements 6

With	Why it matters	Importance	Evidence	What to do
Ciprofloxacin and similar antibiotics that bind metals prescription	Metal ions in the fennel extract may bind the antibiotic in the gut, as they do with calcium and iron products.	In rats, an aqueous fennel extract cut ciprofloxacin peak levels by 83% and total exposure by 48%. No human study was found. If the same happened in people, the antibiotic could fail to reach effective levels.	Animal research Very low certainty ⁹⁰	Ask a pharmacist before taking fennel tea or supplements while on ciprofloxacin or related antibiotics; the study authors suggest a gap between doses.
Hormonal contraception, including the DMPA injection, and menopausal hormone therapy prescription	Fennel produced bleeding in women who had stopped bleeding on DMPA, so it may affect the womb lining or hormone balance.	In 78 women with DMPA-induced amenorrhoea, bleeding occurred in 73% on fennel, 81% on a contraceptive pill and 19% on placebo. How fennel affects contraceptive effectiveness has not been studied.	Controlled trial Low certainty ⁵⁵	Tell the prescriber if you use fennel supplements with hormonal contraception or hormone therapy.
Tamoxifen, aromatase inhibitors and other anti-oestrogen cancer drugs prescription	Theory only: fennel compounds showed oestrogen-like activity in lab cells, which could in principle oppose anti-oestrogen treatment.	No human study of fennel with these drugs was found, and a human trial did not show a rise in oestradiol with fennel. The EU monographs list no interaction.	Pharmacological theory Not enough evidence ^{62 28 92}	Ask the oncology team before using fennel supplements, teas or oils.
Anti-seizure medicines and epilepsy prescription	A seizure followed ingestion of fennel essential oil in a woman taking anti-seizure treatment.	One case report only; the amount and product were unknown.	Case report Very low certainty ⁸²	People with epilepsy should avoid fennel essential oil and ask their neurologist about concentrated fennel products.
Blood thinners, diabetes medicines, blood pressure medicines and other prescription drugs prescription	Not studied.	The EU monographs state no interactions have been reported. Absence of reports is not evidence of safety, because few interaction studies have been done. A rat study found lower blood sugar after fennel oil (animal only).	Authoritative guidance Not enough evidence ^{92 93 100}	Tell your pharmacist about fennel supplements or regular medicinal teas.
Other herbs and foods containing estragole (basil, tarragon, anise) or the same family herbal	Total daily estragole from all sources adds up; the EU says total exposure should be considered.	Baseline dietary estragole is estimated at 0.5 to 5 mg a day (draft statement). Fennel tea adds to this. Some herbs contain compounds that block estragole activation in lab tests (flavonoids, nevadensin from basil), but this was not shown for fennel.	Authoritative guidance Low certainty ^{91 8 7 92}	Do not use several estragole-rich herbal products at once.

Who should check first 7

Situation	Advice	Evidence
Allergy to fennel, to carrot-family plants (aniseed, caraway, celery, coriander, dill), to anethole, or to mugwort pollen	Do not use fennel fruit preparations (EU monographs).	Authoritative guidance ^{92 93}
Children under 4 years	Fennel fruit preparations are not recommended because of lack of adequate data (EU monographs). Speak to a paediatrician about colic remedies.	Authoritative guidance ^{92 93}
Children 4 to 12 years	Short use only (less than one week), not recommended if estragole exceeds 1.0 microgram per kg body weight a day unless a risk assessment justifies it; use for menstrual spasm is not recommended under 12 (EU monographs).	Authoritative guidance ^{92 93}
Pregnancy and breastfeeding	Use is not recommended (EU monographs); estragole must stay below 0.05 mg per person a day. Speak to a midwife or doctor.	Authoritative guidance ^{92 93 96}
Epilepsy	Avoid fennel essential oil; a seizure case has been reported. Not an official contraindication for the fruit.	Case report ⁸²
Oestrogen-sensitive cancer or conditions, hormone treatment	Not an EU contraindication, but ask your specialist first because of fennel's weak oestrogen-like lab activity and bleeding effect in women on hormones.	Laboratory research ^{62 55 92}
Use for longer than 2 weeks in adults	The EU monographs say not to take fennel fruit medicinal tea for more than 2 weeks.	Authoritative guidance ^{92 93}

Overdose, product quality and regulators

Summary. Fennel fruit eaten as a spice or drunk as a tea is common and widely used. The EU reports no case of overdose. The main toxic concern is estragole, which causes DNA damage and liver tumours in rodents at doses far above human intake, and the essential oil, which concentrates it.

Animal. Estragole caused liver tumours in female mice fed 2,300 or 4,600 mg per kg of diet for 12 months (56% and 71% with liver tumours; draft EMA statement, citing Miller 1983); benchmark dose limits were 9 to 33 mg/kg/day. NTP 3-month rat and mouse studies found mild anaemia, raised liver enzymes and liver weight at 75 mg/kg a day and above. An aqueous fennel seed extract caused dose-dependent birth defects in mice given it from day 6 to 15 of pregnancy (EU monograph).

Human doses studied. Fennel tea containing 2.2 mg estragole per 500 mL was given to 12 volunteers and was fully cleared in 8 hours with large differences between people. Capsule trials of fennel up to 2 g seed powder a day for 8 weeks and fennel tea for four weeks (pilot) have been done; no serious events were mentioned in the abstracts that report safety.

High dose or long term signals. Haemoglobin adducts (a marker of exposure to reactive estragole and anethole metabolites) rose in volunteers drinking fennel tea for four weeks and fell after stopping. The meaning for health is unknown. A single infant case of breast development and a seizure after fennel oil are the only human toxicity signals found, apart from allergy.

Overdose response. The EU monographs state no cases of overdose have been reported.

Genotoxicity. Estragole is a weak direct-acting genotoxin in cells and, after liver activation, forms DNA adducts; anethole forms the same adduct types at lower levels. In a human liver cell model, fennel seed powder did not damage DNA, but the oil was toxic to cells at the highest dose. A fennel aqueous extract was negative in the Ames test, and anethole showed weak mutagenic activity in animals (EU monograph). The EU says estragole is a genotoxic carcinogen in rodents.

Toxic plant parts. The fruit (seed) is the part used medicinally; the stem and bulb are eaten as a vegetable. Essential oil is concentrated; estragole in oil of bitter fennel is 3.5 to 12% in the draft EMA statement, and EFSA lists up to 6.1% for bitter oil and up to 5.0% for sweet oil. Do not confuse fennel with poisonous umbellifers such as poison hemlock when picking wild plants.

Product quality is the main practical risk: estragole content varies hugely, tea bags have been linked to Salmonella, oils are often adulterated, and home-prepared fennel purée made infants ill when it was badly stored.

Salmonella in tea bags. In 2002-2003 an outbreak of Salmonella Agona in German infants was linked to an aniseed-fennel-caraway infusion in tea bags and to untreated aniseed from Turkey. ⁷⁴

Methaemoglobinaemia from homemade fennel purée. Four Swiss infants became blue and needed treatment with methylene blue after eating homemade fennel purée; they recovered. The authors blame improper handling and storage of vegetables. ⁵⁹

Adulteration of fennel and anethole oils. Of 30 commercial anethole-type oils tested, 27% were adulterated. A 2026 study notes fennel oil is open to fraud with anise, dill, caraway or cumin oils. ^{60 49}

Estragole content varies widely. Estragole in dry fennel preparations ranged from 0.15 to 13.3 mg per gram; teas from tea bags contained 241 to 2,058 micrograms per litre; some instant teas aimed at infants had relatively high levels. ^{99 75 53}

Furocoumarins (sun-sensitising compounds). Content in fennel fruit was low: up to 1.22 micrograms a day at the highest EU monograph amount, below the strictest recommendations. ⁴³

Pyrrolizidine alkaloids in herbal teas. A Turkish market survey found traces of these plant toxins in all tested teas and herbs including fennel tea (total range 4.6 to 1,054.5 ng per g across all products); a separate fennel figure is not given in the abstract. ³⁶

Body	Action	Date
European Medicines Agency, HMPC (European Union)	EU herbal monograph on bitter fennel fruit (Foeniculum vulgare subsp. vulgare var. vulgare, fructus), final Revision 1 (EMA/HMPC/372841/2016): traditional use for mild spasmodic stomach complaints including bloating and gas, minor menstrual spasm and cough with colds; not for adult use beyond 2 weeks; not recommended under 4 years; limits for 4 to 12 years; contraindicated in hypersensitivity to Apiaceae, anethole or mugwort pollen; pregnancy and breastfeeding not recommended; estragole below 0.05 mg per person a day in pregnancy and breastfeeding and below 1.0 microgram per kg a day in children under 12; allergic reactions possible; no interactions reported; no overdose cases. source	2024-01-31
European Medicines Agency, HMPC (European Union)	EU herbal monograph on sweet fennel fruit (var. dulce), final Revision 1 (EMEA/HMPC/372839/2016): same indications, limits and safety wording as the bitter fennel fruit monograph. source	2024-01-31
European Medicines Agency, HMPC (European Union)	Public statement on the use of herbal medicinal products containing estragole (EMA/HMPC/137212/2005 Rev 1). The 2005 statement concluded that short-term adult use at recommended doses does not pose a significant cancer risk and asked that exposure of young children, pregnant and breastfeeding women be minimised. The revised statement sets the guidance values quoted in the 2024 fennel monographs. source	2014-11-24 (draft read); final revision date not checked
European Medicines Agency, HMPC (European Union)	Meeting report July 2022: draft revised fennel fruit monographs adopted for consultation; because of new safety concerns the HMPC proposed withdrawing the EU monograph on bitter fennel oil and issuing a public statement instead. source	2022-07-20
US National Library of Medicine, LactMed (United States)	Fennel entry: generally well tolerated in adults, fennel oil is generally recognised as safe (GRAS) as a food ingredient per the entry; avoid in people allergic to Apiaceae; excess maternal tea may have caused toxicity in two newborns; may cause photosensitivity; some sources limit use to 2 weeks. source	2026-10-15 (entry date in PubMed record)
European Food Safety Authority, FEEDAP panel (European Union)	2023 opinion on fennel essential oils as animal feed flavourings: low concern at proposed levels; fennel oils are skin and eye irritants and sensitisers, and, with estragole over 1%, are classified as suspected of causing genetic defects and cancer. source	2023-10-30

When to get medical help

Swelling of the face, lips or throat, trouble breathing, wheezing or widespread hives after fennel: call emergency services.
A baby who turns blue or grey, breathes with difficulty, is limp or drowsy after any herbal tea or fennel food: go to emergency care.
A seizure, loss of consciousness or confusion after fennel oil or a product containing it: call emergency services.
Yellow skin or eyes, dark urine, pale stools, severe tiredness or pain in the upper right belly: stop fennel and see a doctor.
Heavy vaginal bleeding, or any bleeding in pregnancy, while using fennel: contact a doctor or midwife.
Breast development, vaginal bleeding or other signs of early puberty in a young child given fennel tea: stop the tea and see a paediatrician.
A baby with fever, bloody diarrhoea or repeated vomiting after herbal tea (Salmonella is possible): seek medical care.
Severe sunburn-like rash or blistering on skin that was exposed to sun after using fennel oil or fresh fennel on the skin: stop and seek advice.

Stop the supplement and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.

General information only, not medical advice. Ask a clinician or pharmacist before use, especially with medicines, in pregnancy or with a health condition. See the Natural Remedy Safety guide.

Frequently asked questions

Does fennel help with infant colic?

Possibly a little, but the evidence is low certainty. A fennel oil emulsion beat placebo in one trial of 125 infants (colic gone in 65% versus 23.7%), a chamomile, fennel and lemon balm extract cut crying time in another, and a pooled result of three fennel-containing trials found about 72 minutes less crying a day, with a very wide range. Reviews call fennel promising but say most trials have high or unclear risk of bias. Talk to a paediatrician first (see the next question).

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Is fennel tea safe for babies?

The EU herbal committee does not recommend fennel fruit preparations in children under 4 years because of lack of adequate data, and limits use at 4 to 12 years to short courses with an estragole cap. Small colic trials reported no side effects. There is one case report of early breast development in a 12-month-old after months of daily fennel tea, and some infant teas have high estragole levels. Ask a paediatrician or pharmacist before giving any fennel product to a baby.

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Does fennel help irritable bowel syndrome or indigestion?

For IBS, one 30-day placebo-controlled trial of capsules combining curcumin and fennel essential oil found better symptom scores, but fennel was not tested alone (low certainty). For indigestion no trial tested fennel alone; one open study used a seven-ingredient supplement. Lab work suggests fennel can relax part of the stomach.

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Does fennel ease period pain?

Many small trials, mostly from Iran, found less period pain with fennel and a similar effect to mefenamic acid, but results across trials differ widely and Cochrane rates the evidence for all supplements in this area low or very low. One trial found ginger worked better than fennel. Fennel capsules or extract may cause heavier bleeding in some women.

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Does fennel help menopause symptoms?

Results are mixed. A 2021 meta-analysis of two small placebo-controlled trials favoured fennel, but a third placebo-controlled trial found no difference because the placebo group also improved. Fennel alone did not clearly help sleep or mood. The one trial that measured blood oestradiol did not show a rise. All were small trials from Iran.

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Does fennel increase breast milk?

We do not know. Cochrane says it is very uncertain whether fennel (or fenugreek) improves infant weight, and milk volume results could not be combined. A safety trial of a fennel-containing tea in 60 breastfeeding mothers found no adverse events but did not test milk supply. The EU says fennel fruit is not recommended during breastfeeding.

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Is fennel safe in pregnancy and breastfeeding?

The EU herbal monographs say safety has not been established and use is not recommended in pregnancy or breastfeeding, partly because of the estragole limit (below 0.05 mg per person a day). Fennel extract caused birth defects in pregnant mice in a study cited by the EU. LactMed says anethole passes into breast milk and that excessive tea seemed to cause toxicity in two newborns. Ask a midwife or doctor.

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What is estragole and should I worry about it?

Estragole is a minor compound in fennel oil that causes DNA damage and liver tumours in rodents at doses far above human intake. The EU says exposure should be kept as low as practically achievable and, in 2005, concluded that short-term adult use at tea doses does not pose a significant cancer risk. Margin-of-exposure studies find a low priority for adults who drink one cup a day, but not for children if use continues long term. The amount varies hugely between products, and the oil is far more concentrated than tea.

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Is fennel a phytoestrogen? Is it safe with breast cancer or hormone treatment?

Fennel is often called a plant oestrogen. In lab cells, a breakdown product of anethole bound the oestrogen receptor and made breast cancer cells grow, and estragole and anethole raised oestrogen in a cell model. In people, one trial found oestradiol did not rise with fennel seed powder, but fennel brought on bleeding in women on a hormonal injection. The EU does not list hormone-sensitive conditions as a contraindication, but if you have an oestrogen-sensitive condition or take hormone treatment, ask your specialist first.

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Does fennel interact with medicines?

The EU monographs report no interactions, but very few have been studied. A rat study found an aqueous fennel extract cut ciprofloxacin absorption (peak level down 83%). Fennel produced bleeding in women on a depot contraceptive injection. No study of fennel with tamoxifen or other hormone treatments was found. Tell your pharmacist about fennel supplements or regular fennel tea.

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What is the difference between bitter and sweet fennel?

They are two varieties used by the EU herbal committee, each with its own monograph carrying the same safety wording. Bitter fennel oil has more estragole in the draft EMA table (3.5 to 12% of the oil versus 1.5 to 5.0% in sweet fennel). Florence fennel is a vegetable type grown for its bulb. Studies often do not say which variety was used.

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Should I be careful with fennel essential oil?

Yes. Oil concentrates anethole and estragole. One case report describes a seizure after eating cakes with fennel oil, EFSA classes fennel oils as skin and airway sensitisers and suspected of causing genetic defects and cancer, and the EU committee proposed withdrawing its monograph on bitter fennel oil in 2022. Many oils are also adulterated.

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Editorial transparency

Written by: AlternativeMed editorial team. Research compiled with AI assistance, then checked against PubMed records.
Medical review: None. This page has not been reviewed by a physician or pharmacist.
First published: 2026-10-25
Last substantive update: 2026-10-25
How we research: We searched PubMed, read the abstracts of the studies cited, read the EU herbal monographs on bitter and sweet fennel fruit, the 2022 HMPC meeting report, the 2014 draft EU public statement on estragole and the US LactMed entry on fennel in full, and checked the plant name, chemical IDs and food data against GBIF, NCBI, PubChem and USDA FoodData Central. One retracted paper was skipped.
How we rate evidence: See "How we rate evidence" in the Evidence tab.
Independence: No product is promoted on this page. No affiliate links are shown. If one is added later it will be labelled and kept apart from the evidence.

Sources 100

Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.

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