Gyokuro: shaded, steamed and dried green tea leaf.

Gyokuro

Q: What is gyokuro?

Gyokuro is a Japanese green tea made from Camellia sinensis. The plants are shaded with screens or cloth for about 20 days before harvest, and the leaves are then steamed and dried. Shading gives a leaf high in theanine.

Q: How much caffeine and theanine does gyokuro contain?

In a 2025 Japanese lab study, dry gyokuro leaf held 35.41 mg of caffeine and 30.84 mg of theanine per gram, more of both than the sencha types tested (24.70 to 31.01 mg caffeine and 17.65 to 20.37 mg theanine per gram). These are lab averages of blended market samples, and real products vary.

Q: Is gyokuro stronger in caffeine than other green teas?

Per gram of leaf, yes in that study. In the authors' own test infusions gyokuro also came out much stronger than a superior sencha, but it was made with much more leaf in less water, so the comparison is not like for like. The FDA and NHS cup figures for green tea are not measurements of gyokuro.

Q: Is gyokuro the same as matcha?

No. Both come from shaded plants, but gyokuro leaf is steeped and removed, while matcha is shaded leaf ground to powder. They are different products with separate pages.

Q: Does gyokuro calm you down or help focus?

It has not been tested. Theanine and caffeine given as compounds gave a moderate short-term lift in attention, and theanine supplements gave a modest, uncertain effect on stress. The stress result depended on studies at high risk of bias. A mouse study of gyokuro showed a stress marker fell, which does not show the same in people.

Q: Is gyokuro the same as green tea extract?

No. A cup of tea is a water extract of the leaf. Capsules and tablets are concentrated catechins and have been linked to rare serious liver injury. NCCIH reports no safety concerns for the drink in adults. Do not carry safety or benefit results from one to the other.

Q: Can gyokuro hurt the liver?

The drink rarely does. EFSA judged traditional green tea infusions generally safe at European intakes but noted rare liver injury after infusions, most probably an individual reaction. EFSA also found that supplements with high EGCG raised liver enzymes in trials, and LiverTox lists liver failure for extracts. Stop any extract and get medical care if you notice yellow skin or eyes or dark urine.

Q: Is gyokuro safe in pregnancy or breastfeeding?

It is not banned, but it carries a lot of caffeine that counts toward your daily limit. The NHS says no more than 200 mg of caffeine a day in pregnancy, and a 2014 meta-analysis linked higher intake with more miscarriage, stillbirth and low birth weight with no clear safe threshold, though the links may be partly bias. LactMed reports infant fussiness only at extremely high maternal caffeine. Ask your midwife or doctor.

Q: Does gyokuro interact with medicines?

No gyokuro-specific interaction was found. For green tea in general, NCCIH says high doses lowered blood levels of nadolol, the extract lowered atorvastatin, and a study showed an interaction with raloxifene. One 1999 case report links very large amounts of green tea with weaker warfarin effect. Caffeine can also add to other stimulants. Ask your pharmacist or prescriber.

Q: Does gyokuro help with cholesterol, weight or blood pressure?

Not shown for gyokuro. For green tea in general, pooled trials found small and unstable falls in cholesterol and blood pressure and almost no weight change outside Japan. A review of short tea trials found no effect on cholesterol or blood pressure. Evidence is low.

Camellia sinensis · also called Shade-grown green tea, Japanese shaded tea. Not the same as matcha or green tea extract capsules.

Gyokuro is a Japanese green tea made from tea plants shaded for about three weeks before harvest. In a lab study its leaf had more theanine and more caffeine than the other Japanese green teas tested. No trial has tested gyokuro in people: the research is on green tea in general and on theanine and caffeine as compounds, and it shows small or uncertain effects. The main caution is its caffeine, and concentrated extract capsules are a separate product with rare serious liver injury reports.

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

Get your Gyokuro today. Order now from Amazon and have it delivered to your door.Shop Gyokuro tea on AmazonSupport our free guides: as an Amazon Associate we earn from qualifying purchases.

About Gyokuro

Gyokuro is the shade-grown Japanese green tea, rich in theanine and in caffeine. No trial has tested it in people. Research on theanine and caffeine as compounds shows a short-term lift in attention and a modest, uncertain effect on stress. Research on green tea in general shows small or uncertain effects on heart risk factors and none on blood sugar. The main caution is caffeine; concentrated extract capsules are a separate product with rare serious liver injury reports.

What it is

Gyokuro is green tea from Camellia sinensis, a plant of the tea family (Theaceae) that GBIF accepts as a species. It is not a different plant. What sets it apart is the growing: the plants are covered with a reed screen or black cheesecloth for about 20 days after the sprouts appear, and the leaves are then steamed and dried like other Japanese green teas.

Shading changes the leaf. The researchers who measured it describe gyokuro as a premium tea with a particularly high theanine content and a green-laver-like aroma. Matcha is made from shaded leaf ground to powder, and extract capsules are concentrated catechins; each is a different product.

^{35 27 28 32}

What is in the leaf

A 2025 lab study in Japan blended market samples of eight Japanese green teas (gyokuro from Yame, Uji and Asahina) and measured the dry leaf. Per gram, gyokuro held 30.84 mg theanine, 35.41 mg caffeine and 53.31 mg EGCG. A superior sencha held 20.37 mg theanine, 31.01 mg caffeine and 67.45 mg EGCG. So gyokuro had the most amino acids and caffeine, and fewer catechins than the sencha types.

The authors also tested infusions, each tea under its own conditions. Gyokuro came out far stronger than sencha in both theanine and caffeine, partly because it was made with much more leaf in much less water. The authors propose that teas whose caffeine and EGCG are small next to their theanine and arginine may relieve stress, and say gyokuro fits that. That idea comes from animal and earlier work and has not been tested with gyokuro in people. These are one year of blended market samples; real products vary.

^{27 28 26}

Gyokuro, matcha, sencha or extract?

A cup of gyokuro is a water extract of the leaf. A capsule or tablet packs catechins into a concentrated pill. The liver warnings and many trial results belong to the concentrated form. A systematic review of 159 human studies found liver events came from concentrated, catechin-rich preparations taken in large single doses, and not from brewed tea or extracts used in drinks or food. Do not carry results from one form to the other, and do not carry results from theanine tablets to a cup of gyokuro.

^{12 5 32}

What the research shows

No trial of gyokuro in people was found. For attention, one pooled analysis of 11 one-off-dose trials found a moderate lift from caffeine and theanine together in the first two hours, driven partly by caffeine, and a 2026 pooled analysis of 31 theanine trials found faster choice reaction times. The same analysis found a modest stress effect that depended on studies at high risk of bias, inconsistent anxiety results, and a small depression effect that needs confirming. A 30-person tablet trial, funded by the supplement maker, saw better mood and sleep scores. A mouse study found that gyokuro and low-caffeine sencha reduced a stress marker.

For green tea in general, Cochrane found small and unstable falls in cholesterol and blood pressure, a later review of short tea trials found no effect, and weight loss outside Japan was almost nil. Cancer results were inconsistent and low in certainty. Heavy drinkers in Japan had lower death rates, which shows a link and not a cause. Trials of green tea supplements in type 2 diabetes found no effect on blood sugar.

^{4 7 11 26 9 14 16 6 1 3 22 29 18}

Fluoride and contaminants

Tea plants take up fluoride from the soil, and longer brewing releases more. A review of 88 studies found average fluoride in green tea (1.37 mg/L) was lower than in black or brick tea; that is a green tea average, not a gyokuro measurement. No measured lead, cadmium, aluminium or pesticide figures for gyokuro were found in the sources read, so that is unknown, not shown safe.

^{15 23}

Regulators and status

The EMA has an EU herbal monograph and assessment report for green tea leaf; only the web page was read and it does not name gyokuro. EFSA judged traditional infusions generally safe at European intakes. NCCIH notes that the FDA approved a green tea extract ointment as a prescription drug for genital warts, which is a topical medicine and not a drink or supplement.

^{34 5 32}

At a glance

Traditional uses history, not proof

Gyokuro is a high-grade Japanese green tea; the growers cover the tea field with a reed screen or black cheesecloth for about 20 days after the sprouts appear (Unno 2025).
Tea itself was first grown in China thousands of years ago, and NCCIH says it has been used for health purposes for about 3,000 years.
Today green tea and its extracts are promoted as supplements for weight loss, lower cholesterol and prevention of chronic disease (NCCIH).

Studied for research

Alertness and attention (from caffeine plus theanine as compounds), low
Stress and mood (from theanine supplements and a mouse study), low
Sleep quality (one small theanine tablet trial), very low
Cholesterol (green tea in general), low
Blood pressure (green tea in general), low
Body weight (green tea in general), low
Cancer risk (green tea in general), insufficient
Blood sugar in type 2 diabetes (green tea supplements), no effect found (against)

Main compounds

Theanine (very high for a green tea)
Caffeine (highest of the Japanese green teas measured)
Catechins, mainly EGCG (lower than sunlit sencha)
Arginine and other amino acids

Common forms

Loose leaf gyokuro, brewed as a drink
Shaded leaf ground to powder is matcha (separate page)
Concentrated green tea extract capsules and tablets (a different product with a liver warning)

Research links: NCCIH: Green Tea · Unno 2025: Japanese green tea composition, gyokuro included (open access) · EFSA opinion on green tea catechins (abstract) · Meta-analysis of L-theanine trials, 2026 (abstract) · LiverTox: Green Tea (summary) · FDA: How much caffeine is too much · NHS: foods to avoid in pregnancy (caffeine) · Research Library · Genes & Biomarkers Library

What it is and its history

Accepted scientific name: Camellia sinensis
Naming authority: (L.) Kuntze
Synonyms: Camellia bohea (L.) Sweet; Camellia chinensis (Sims) Kuntze; Camellia cantonensis Lour.
Common names: Gyokuro (Japanese); Shaded green tea (English)
Family or group: Theaceae (the tea family)
Classification: Plantae > Ericales > Theaceae > Camellia > Camellia sinensis
Native range: Not checked in the sources read (NCCIH says tea was first cultivated in China thousands of years ago).
Habitat: Not checked.
What it looks like: Stems: Stems are present in some tea products (LactMed).; Leaves: The leaf is the part used; steamed, pan fried and dried but not fermented for green tea (NCCIH).; Flowers: Not checked.; Fruit: Not checked.
Cultivation: Shaded before harvest for about 20 days (Unno 2025). The study's gyokuro samples came from Fukuoka (Yame), Kyoto (Uji) and Shizuoka (Asahina).
Harvest and processing: Gyokuro is cultivated by covering the tea field with a reed screen or black cheesecloth for about 20 days as soon as the sprouts appear, then the leaves are steamed and dried like other Japanese green teas (Unno 2025). Shading raises theanine and gives gyokuro a green-laver-like aroma.
Look-alikes and adulterants: Name: Matcha, sencha and extract capsules; Note: Matcha is made from shaded leaf (tencha) ground to powder; sencha is grown in direct sun; extract capsules are concentrated catechins. Each is a different product.
Sustainability and conservation: Not checked.

Photographs

Dark green rolled gyokuro tea leaves in a small dish beside a small cup of pale green tea — Gyokuro: shaded, steamed and dried green tea leaf.

Traditional use and history history, not clinical proof

Tradition or era	Documented use	Source
Japanese tea growing	The 2025 Foods paper describes gyokuro as a high-grade Japanese green tea shaded for about 20 days before harvest. No historical dates were read in a source.	p39796392
China, early use of tea	NCCIH says tea was first cultivated in China thousands of years ago and used for health purposes for about 3,000 years.	s-nccih-green-tea
European herbal medicine	EMA has an EU herbal monograph for green tea leaf; its wording was not read and it does not name gyokuro.	s-ema-hmpc-green-tea

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

What is inside, and how it may work

What it 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
Epigallocatechin gallate (EGCG) PubChem 65064	catechin (polyphenol)	Leaf Gyokuro leaf 53.31 mg per g, lower than the 61.61 to 67.45 mg per g of the sencha types tested (Unno 2025).	Liver effects at high supplement doses; other actions not established in the sources read. ^{36 5 24 27}	Human data
Caffeine PubChem 2519	purine alkaloid	Leaf Gyokuro leaf 35.41 mg per g, sencha types 24.70 to 31.01 mg per g (Unno 2025, lab measurement). FDA lists 37 mg in a 12 fl oz drink of green tea in general.	Stimulant; see Safety tab. ^{37 31 27}	Human data
L-theanine PubChem 439378	amino acid	Leaf Gyokuro leaf 30.84 mg per g against 17.65 to 20.77 mg per g in the sencha and steamed tamaryokucha types tested (Unno 2025).	Reviewers link benefits for attention to caffeine and L-theanine together. ^{38 18 19 27 28}	Human data
Tannins and other polyphenols	polyphenols	Leaf and stem Not given.	Tea polyphenols lower iron absorption (radio-iron study, black and herb teas). ^{19 13}	Human data
Arginine	amino acid	Leaf Gyokuro leaf 9.72 mg per g against 2.56 to 6.73 mg per g in the other green teas tested (Unno 2025).	Proposed with theanine to reduce stress in the authors' framework; not shown in people. ²⁷	Lab measurement

Mechanisms, receptors and pathways

Target or pathway	Gene or receptor	What was found	Level
Liver injury from concentrated EGCG	UGT1A4 and COMT variants (secondary trial analysis); an immune-related gene variant (NCCIH)	Toxicology review: liver is the target organ in lab studies, tied to large single doses and fasting and to EGCG content. In a secondary trial analysis, women with the UGT1A4 A/C variant had larger ALT rises on high-dose extract. ^{12 2 32}	Lab and human
Caffeine plus L-theanine on attention	n/a	Cognitive benefits were seen with caffeine and L-theanine together and less with either alone. ¹⁸	Human review
Iron absorption	n/a	Tea polyphenols reduce absorption of non-haem iron in a dose-related way (radio-iron study of black and herb teas). ¹³	Human data
Caffeine and EGCG set against theanine and arginine	n/a	In mice, caffeine and EGCG worked against the anti-stress effect of theanine, while EGC and arginine kept it. A research group turned this into a ratio (CE/TA); gyokuro measured 1.28 in leaf. This is a proposal from lab and mouse work, not a human result. ^{26 27 28}	Mouse and lab

Absorption, metabolism and elimination

Absorption: Not covered in the sources read.
Distribution: Not covered.
Metabolism: A secondary trial analysis links the enzymes COMT and UGT1A4 with liver enzyme changes on high-dose extract.
Elimination: Not covered.
Bioavailability: Not covered.

^{2 32}

Isolated compounds versus whole extracts

Brewed gyokuro, powdered shaded leaf (matcha), liquid extracts and concentrated EGCG capsules are different products. EFSA estimates that supplements can deliver far more EGCG than infusions do; liver warnings come from the concentrated form. Trial results for theanine tablets or extract cannot be applied to the drink, or the other way round.

Nutritional composition

Green tea is not a source of essential nutrients in the sources read. It contains caffeine, L-theanine, catechins and tannins.

10benefits and uses looked at

38studies and sources checked

Low certaintybest evidence rating found

7lab markers tracked in trials

6 low certainty2 very low certainty1 not enough evidence1 evidence against

What was looked at

The 10 benefits and uses checked for Gyokuro, each with how strong the evidence is. Tap one to open it.

Alertness and attentionLow certainty
Stress and moodLow certainty
Sleep qualityVery low certainty
CholesterolLow certainty
Blood pressureLow certainty
Body weightLow certainty
Heart disease and death rates in drinkersLow certainty
Cancer riskNot enough evidence
Dementia and memory loss riskVery low certainty
Blood sugar in type 2 diabetesEvidence against

Lab markers tracked in the studies

Choice reaction timeTheanine in the dry leafLDL cholesterolSystolic blood pressureBody weightDeath from any causeHbA1c

What is Gyokuro good for?

The uses people ask about and how strong the human evidence is for each. No trial tested gyokuro itself. Results below are for theanine and caffeine as compounds, or for green tea in general, and are labelled that way.

Alertness and attentionLow certaintyCaffeine and theanine together, given as compounds, gave a moderate short-term lift in alertness and attention; a pooled analysis of theanine supplements found faster choice reaction times. Part of the effect is the caffeine. Gyokuro was not tested. Stress and moodLow certaintyTheanine supplements gave a modest drop in acute stress, mostly in studies at high risk of bias, and inconsistent results for anxiety. For gyokuro itself there are lab measurements and one mouse study only. Sleep qualityVery low certaintyOne small four-week trial of theanine tablets (industry-funded) saw better sleep scores. Gyokuro also has a lot of caffeine. Cholesterol (green tea in general)Low certaintyPooled trials of green tea drinks and extracts found small falls, but a later review of shorter trials found no effect. Blood pressure (green tea in general)Low certaintyA 2025 review of 36 trials found average falls of about 1 mmHg with big differences between trials. A review of short tea trials found no effect. Body weight (green tea in general)Low certaintyA Cochrane review found almost no weight change outside Japan. Heart disease and death rates in drinkers (green tea in general)Low certaintyIn eight Japanese cohorts, people who drank five or more cups a day had lower all-cause death than those who drank under one cup. This is an association only. Cancer risk (green tea in general)Not enough evidenceA Cochrane review of 142 studies found limited, inconsistent, low-certainty results. Dementia and memory loss risk (green tea in general)Very low certaintyEight observational studies gave mixed results. Blood sugar in type 2 diabetes (green tea supplements)Evidence againstA meta-analysis of 14 trials found no significant effect on blood sugar measures.

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.

Alertness and attention

Low certainty

Gyokuro is rich in both caffeine and theanine. Trials of caffeine and theanine taken together (as compounds, not as gyokuro tea) show a moderate short-term lift in alertness and attention. Part of that comes from the caffeine. Nobody has tested a cup of gyokuro.

4 studiesIsolated compounds and mixed green tea products. No gyokuro drink was…

Studies, doses and limits

What the trials found

Camfield 2014 pooled 11 placebo-controlled one-off-dose trials of theanine, EGCG and caffeine as compounds. Gerolymos 2026 pooled 31 trials of oral L-theanine supplements. Mancini 2017 reviewed 21 mixed green tea studies. None tested gyokuro.

Results

Moderate effect sizes for caffeine plus theanine on alertness and attention-switching accuracy in the first 2 hours (Camfield 2014). A single theanine dose improved choice reaction time, SMD 0.51 (95% CI 0.25 to 0.77) (Gerolymos 2026). Mancini 2017 reports better attention and memory with green tea, with no numbers in the abstract.

Effect sizes as reported

Moderate and short-lived in the compound trials.

Why this rating

The evidence is for compounds and mixed green tea products, not gyokuro; effects last about two hours and partly come from caffeine.

Form and dose studied

Isolated compounds and mixed green tea products. No gyokuro drink was tested.

Who was studied

Mostly healthy adults.

Limits

No gyokuro trial. One author of the 2026 review founded a supplement company. Abstracts only were read.

Why researchers looked

Gyokuro is shade-grown, which raises its theanine, and it also holds a lot of caffeine. Theanine plus caffeine is the pairing studied for calm alertness.

Traditional use

Not described in the sources read.

Proposed mechanism Human study observation

A review of 11 trials saw larger changes with the caffeine dose than the theanine dose in the first hour. A review of green tea studies says benefits for thinking appeared with caffeine and theanine together and less with either alone.

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

Gyokuro also carries a lot of caffeine; see the Safety tab.

^{4 7 18 27}

Stress and mood

Low certainty

Theanine, the amino acid gyokuro is rich in, has been tested as a supplement for stress and mood with modest and uneven results. For gyokuro itself there are only lab measurements and one mouse study.

5 studiesTheanine supplements in people; gyokuro tea only in mice.

Studies, doses and limits

What the trials found

Gerolymos 2026 (31 trials, n = 1,168) tested theanine supplements, not tea. Hidese 2019 tested theanine tablets in 30 healthy adults.

Results

Acute stress fell modestly (SMD 0.31), largely in studies at high risk of bias; anxiety results were inconsistent and mostly not significant; depressive symptoms fell after a single dose once one outlier was removed (SMD 0.69, 95% CI 0.13 to 1.25). In the 30-person crossover trial, depression, trait anxiety and sleep scores improved against placebo over four weeks. In mice, gyokuro and low-caffeine sencha reduced stress-related adrenal enlargement.

Effect sizes as reported

Modest and uncertain.

Why this rating

Supplement trials, small or biased, one industry-funded; the gyokuro evidence is lab and mouse only.

Form and dose studied

Theanine supplements in people; gyokuro tea only in mice.

Who was studied

Healthy adults; mice.

Limits

No gyokuro trial in people. The small trial was funded by the supplement maker, and two authors work for it.

Why researchers looked

Shading the tea plants raises theanine, and theanine is studied for relaxation.

Traditional use

Not described in the sources read.

Proposed mechanism Hypothesis

A Japanese research group proposes that a tea whose caffeine and EGCG are small next to its theanine and arginine (a ratio below 3) may relieve stress. They measured gyokuro below that line. This is their inference from animal and earlier work, not a trial of gyokuro.

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

Caffeine in gyokuro can itself cause jitters and poor sleep; see the Safety tab.

^{7 11 26 27 28}

Sleep quality

Very low certainty

One small supplement trial saw better sleep scores with theanine tablets. Gyokuro carries a lot of caffeine, which can work against sleep.

1 studiesTheanine tablets.

Studies, doses and limits

What the trials found

A 30-person four-week crossover trial of theanine tablets (not tea).

Results

The Pittsburgh Sleep Quality Index score fell after theanine compared with placebo (p = 0.013), with lower sleep latency, sleep disturbance and sleep medication use sub-scores.

Effect sizes as reported

Not given as an effect size in the abstract.

Why this rating

One small, industry-funded trial of tablets, not gyokuro.

Form and dose studied

Theanine tablets.

Who was studied

30 healthy adults.

Limits

Single trial; supplier-funded; self-rated scores.

Why researchers looked

Theanine is sold for relaxation and sleep.

Traditional use

Not described in the sources read.

Proposed mechanism Not established

Not established in the sources read.

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

Caffeine in gyokuro can disturb sleep.

¹¹

Cholesterol

Low certainty

Pooled trials of green tea drinks and extracts show a small average fall in total and LDL cholesterol. Two reviews disagree, and most of the trial data comes from extract or mixed products, so the result for a cup of tea is uncertain.

4 studiesMixed green tea drinks and extracts from many teas. No trial tested g…

Studies, doses and limits

What the trials found

A 2011 meta-analysis of 14 trials (1,136 people) of green tea drinks or extracts found a small fall in total and LDL cholesterol and no change in HDL. A Cochrane review of 7 green tea trials found larger falls that were not stable when checked. A 2020 review of 14 shorter trials of green or black tea (4 to 24 weeks) found no significant effect. NCCIH says most trials tested extract supplements, not the drink.

Results

Total cholesterol -7.20 mg/dL (95% CI -8.19 to -6.21) and LDL -2.19 mg/dL (-3.16 to -1.21) in the 2011 pooled trials; Cochrane green tea: total -0.62 mmol/L and LDL -0.64 mmol/L, not stable to sensitivity analysis; 2020 review: no significant change.

Effect sizes as reported

Small average falls; reviewers disagree on whether they are real in short trials.

Why this rating

Pooled drinks and extracts, small trials, results not stable, a later review found no effect.

Form and dose studied

Mixed green tea drinks and extracts from many teas. No trial tested gyokuro as a drink. This result is for green tea or the compound named.

Who was studied

Healthy adults and adults at higher risk, mostly short trials.

Limits

Product types differ; most trials are short; no heart attack or stroke outcomes. No gyokuro-specific trial exists.

Why researchers looked

High LDL cholesterol is a risk factor for heart disease, and green tea catechins are often said to help.

Traditional use

Not described in the sources read.

Proposed mechanism Not established

No mechanism was established in the sources read.

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

^{29 9 14 32}

Blood pressure

Low certainty

Reviews find a very small average fall in blood pressure, with big differences between studies. One review of short trials found no effect.

3 studiesMixed green tea drinks and extracts from many teas. No trial tested g…

Studies, doses and limits

What the trials found

A 2025 meta-analysis of 36 trials of green tea supplementation found average falls of about 1 mmHg in both systolic and diastolic pressure with very high differences between trials. The Cochrane review found larger falls (about 3 mmHg) from a small number of green tea trials that were not stable. A 2020 review of 14 trials of green or black tea (4 to 24 weeks) found no significant effect.

Results

Systolic -1.08 mmHg (95% CI -1.98 to -0.18), diastolic -1.09 mmHg (-1.67 to -0.50) in 36 trials; Cochrane green tea systolic -3.18 mmHg, diastolic -3.42 mmHg, unstable; 2020 review: no significant effect.

Effect sizes as reported

About 1 to 3 mmHg at most.

Why this rating

Very large differences between trials (I2 74 to 85 percent), unstable Cochrane result, one review with no effect.

Form and dose studied

Mixed green tea drinks and extracts from many teas. No trial tested gyokuro as a drink. This result is for green tea or the compound named.

Who was studied

Adults, with stronger effects in people who started with raised blood pressure.

Limits

Heterogeneity; mixed forms; small average change that may not matter to health. No gyokuro-specific trial exists.

Why researchers looked

High blood pressure is a leading risk factor for heart disease and stroke.

Traditional use

Not described in the sources read.

Proposed mechanism Not established

No mechanism was established in the sources read.

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

Brewed green tea has no safety concerns reported in adults (NCCIH) but contains caffeine. Concentrated extract capsules are a different product with rare serious liver injury reports. See the Safety tab. The authors call green tea a complementary approach, not a treatment for high blood pressure.

^{22 9 14}

Body weight

Low certainty

A Cochrane review found almost no weight loss from green tea outside Japan. The Japanese trials were too different to combine and ranged from little change to a few kilograms.

2 studiesMixed green tea drinks and extracts from many teas. No trial tested g…

Studies, doses and limits

What the trials found

The review included trials of at least 12 weeks in overweight or obese adults: six outside Japan (532 people) and eight in Japan (1,030 people).

Results

Outside Japan: weight -0.04 kg (95% CI -0.5 to 0.4), BMI -0.2 kg/m2, waist -0.2 cm; none significant. Japanese trials ranged from -0.2 to -3.5 kg and could not be pooled.

Effect sizes as reported

No meaningful change outside Japan.

Why this rating

Short trials of 12 to 13 weeks, many preparation types, results differ by region.

Form and dose studied

Mixed green tea drinks and extracts from many teas. No trial tested gyokuro as a drink. This result is for green tea or the compound named.

Who was studied

Overweight and obese adults.

Limits

Not a drink-only result; short. No gyokuro-specific trial exists.

Why researchers looked

Green tea contains catechins and caffeine, which reviewers say are believed to raise energy use.

Traditional use

NCCIH says green tea and extracts are promoted for weight loss.

Proposed mechanism Hypothesis

The Cochrane reviewers state a belief that catechins and caffeine may raise energy metabolism; they say the efficacy remains unclear.

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

^{16 32}

Heart disease and death rates in drinkers

Low certainty

In Japan, people who drank five or more cups a day had somewhat lower death rates than people who drank less than one. This is an association and does not show tea caused it.

2 studiesMixed green tea drinks and extracts from many teas. No trial tested g…

Studies, doses and limits

What the trials found

A pooled analysis of eight Japanese cohorts followed 313,381 people for a mean 17.3 years.

Results

Five or more cups a day versus less than one: all-cause death HR 0.90 (0.87 to 0.94) in men and 0.82 (0.74 to 0.90) in women; heart disease HR 0.82 and 0.75; stroke-type HR 0.76 and 0.78. In women only, total cancer death HR 0.89 (0.83 to 0.96) at 1 to 2 cups.

Effect sizes as reported

Roughly 10 to 18 percent lower all-cause death among the heaviest drinkers.

Why this rating

Observational; healthier lifestyle among drinkers cannot be ruled out; Japanese data.

Form and dose studied

Mixed green tea drinks and extracts from many teas. No trial tested gyokuro as a drink. This result is for green tea or the compound named.

Who was studied

Japanese adults.

Limits

Self-reported intake; cannot show cause; may not apply outside Japan. No gyokuro-specific trial exists.

Why researchers looked

Green tea is part of daily life in Japan, so large cohorts can compare heavy and light drinkers.

Traditional use

NCCIH notes that lower heart disease risk has been linked to green tea in Asian but not Western groups.

Proposed mechanism Not established

Not established. Observational data cannot identify a mechanism.

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

^{1 32}

Cancer risk

Not enough evidence

A large Cochrane review found inconsistent, low-certainty results. It does not show that green tea prevents cancer.

2 studiesMixed green tea drinks and extracts from many teas. No trial tested g…

Studies, doses and limits

What the trials found

The review used 142 studies: 11 trials of green tea extract (1,795 people) and 131 observational studies (over 1,100,000 people).

Results

Extract trials: prostate cancer RR 0.50 (95% CI 0.18 to 1.36), gynaecological RR 1.50 (0.41 to 5.48), skin RR 1.00 (0.06 to 15.92). Observational highest versus lowest intake: cancer incidence RR 0.83 (0.65 to 1.07); cancer death RR 0.99 (0.91 to 1.07). Results conflicted between study designs for some cancers.

Effect sizes as reported

Intervals include no effect.

Why this rating

Low-certainty and inconsistent results; mostly observational; Asian populations.

Form and dose studied

Mixed green tea drinks and extracts from many teas. No trial tested gyokuro as a drink. This result is for green tea or the compound named.

Who was studied

Adults, mostly in Asia.

Limits

Cannot show cause; trials used extract. No gyokuro-specific trial exists.

Why researchers looked

Lab studies have suggested catechins may slow cancer cell growth; population studies have asked whether tea drinkers get less cancer.

Traditional use

Not described in the sources read.

Proposed mechanism Lab only

Cochrane notes that laboratory studies have suggested catechins may inhibit cancer cell growth. This is lab work and not shown in people.

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

^{6 32}

Dementia and memory loss risk

Very low certainty

Observational studies lean towards lower risk in green tea drinkers, but they are few and mixed, and cannot show that tea is the reason.

1 studiesMixed green tea drinks and extracts from many teas. No trial tested g…

Studies, doses and limits

What the trials found

A 2019 systematic review found 3 cohort and 5 cross-sectional studies.

Results

One cohort and three cross-sectional studies supported a benefit, one cohort and one cross-sectional study partly supported it, and one of each found no link.

Effect sizes as reported

Not given in the abstract.

Why this rating

Eight observational studies, mixed results, cannot show cause.

Form and dose studied

Mixed green tea drinks and extracts from many teas. No trial tested gyokuro as a drink. This result is for green tea or the compound named.

Who was studied

Mostly Asian adults.

Limits

Observational; small number of studies. No gyokuro-specific trial exists.

Why researchers looked

Population studies in Asia asked whether regular green tea drinkers keep their memory longer.

Traditional use

Not described in the sources read.

Proposed mechanism Not established

Not established.

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

¹⁷

Blood sugar in type 2 diabetes

Evidence against

A meta-analysis of 14 trials found no significant effect of green tea supplements on blood sugar measures in people with type 2 diabetes.

1 studiesMixed green tea drinks and extracts from many teas. No trial tested g…

Studies, doses and limits

What the trials found

A 2021 meta-analysis pooled 14 randomised trials in people with type 2 diabetes.

Results

No significant effect on fasting glucose, fasting insulin, HbA1c or insulin resistance (HOMA-IR).

Effect sizes as reported

No significant effect.

Why this rating

One meta-analysis of 14 trials found no effect; the abstract does not give the product type; small trials, so no effect is not proof of none.

Form and dose studied

Mixed green tea drinks and extracts from many teas. No trial tested gyokuro as a drink. This result is for green tea or the compound named.

Who was studied

Adults with type 2 diabetes.

Limits

Small trials; form unclear. No gyokuro-specific trial exists.

Why researchers looked

Catechins have been proposed to affect blood sugar and insulin.

Traditional use

Not described in the sources read.

Proposed mechanism Not established

Not established in the source read.

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

Brewed green tea has no safety concerns reported in adults (NCCIH) but contains caffeine. Concentrated extract capsules are a different product with rare serious liver injury reports. See the Safety tab. People taking diabetes medicines should speak to their prescriber before using any supplement.

Connections to the rest of health

How Gyokuro 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
Mental Clarity		Low certainty	Alertness and attention: Gyokuro is rich in both caffeine and theanine. Trials of caffeine and theanine taken together (as compounds, not as gyokuro tea) show a moderate short-term lift in alertness and attention. Part of that comes from the caffeine. Nobody has tested a cup of gyokuro.	^{4 7 18 27}
Better Focus		Low certainty	Alertness and attention: Gyokuro is rich in both caffeine and theanine. Trials of caffeine and theanine taken together (as compounds, not as gyokuro tea) show a moderate short-term lift in alertness and attention. Part of that comes from the caffeine. Nobody has tested a cup of gyokuro.	^{4 7 18 27}
Stress Relief		Low certainty	Stress and mood: Theanine, the amino acid gyokuro is rich in, has been tested as a supplement for stress and mood with modest and uneven results. For gyokuro itself there are only lab measurements and one mouse study.	^{7 11 26 27 28}
Mood Balance		Low certainty	Stress and mood: Theanine, the amino acid gyokuro is rich in, has been tested as a supplement for stress and mood with modest and uneven results. For gyokuro itself there are only lab measurements and one mouse study.	^{7 11 26 27 28}
Sleep Support		Very low certainty	Sleep quality: One small supplement trial saw better sleep scores with theanine tablets. Gyokuro carries a lot of caffeine, which can work against sleep.	¹¹
Cholesterol Balance		Low certainty	Cholesterol: Pooled trials of green tea drinks and extracts show a small average fall in total and LDL cholesterol. Two reviews disagree, and most of the trial data comes from extract or mixed products, so the result for a cup of tea is uncertain.	^{29 9 14 32}
Heart Health		Low certainty	Cholesterol: Pooled trials of green tea drinks and extracts show a small average fall in total and LDL cholesterol. Two reviews disagree, and most of the trial data comes from extract or mixed products, so the result for a cup of tea is uncertain. Blood pressure: Reviews find a very small average fall in blood pressure, with big differences between studies. One review of short trials found no effect.	^{29 9 14 32 22}
Blood Pressure Support		Low certainty	Blood pressure: Reviews find a very small average fall in blood pressure, with big differences between studies. One review of short trials found no effect.	^{22 9 14}
Weight Management		Low certainty	Body weight: A Cochrane review found almost no weight loss from green tea outside Japan. The Japanese trials were too different to combine and ranged from little change to a few kilograms.	^{16 32}
Heart Health	Biological association	Low certainty	Heart disease and death rates in drinkers: In Japan, people who drank five or more cups a day had somewhat lower death rates than people who drank less than one. This is an association and does not show tea caused it.	^{1 32}
Longevity	Biological association	Low certainty	Heart disease and death rates in drinkers: In Japan, people who drank five or more cups a day had somewhat lower death rates than people who drank less than one. This is an association and does not show tea caused it.	^{1 32}
Preventive Wellness		Not enough evidence	Cancer risk: A large Cochrane review found inconsistent, low-certainty results. It does not show that green tea prevents cancer.	^{6 32}
Brain Health	Biological association	Very low certainty	Dementia and memory loss risk: Observational studies lean towards lower risk in green tea drinkers, but they are few and mixed, and cannot show that tea is the reason.	¹⁷
Healthy Aging	Biological association	Very low certainty	Dementia and memory loss risk: Observational studies lean towards lower risk in green tea drinkers, but they are few and mixed, and cannot show that tea is the reason.	¹⁷
Blood Sugar Balance		Evidence against	Blood sugar in type 2 diabetes: A meta-analysis of 14 trials found no significant effect of green tea supplements on blood sugar measures in people with type 2 diabetes.	³
Metabolic Health		Evidence against	Blood sugar in type 2 diabetes: A meta-analysis of 14 trials found no significant effect of green tea supplements on blood sugar measures in people with type 2 diabetes.	³

B. Body systems

Connected to	Kind of connection	Evidence status	Context	Studies
Brain Focus	Biological association	Low certainty	Studied for: Alertness and attention Studied for: Stress and mood	^{4 7 18 27 11 26 28 17}
Cardiovascular System	Biological association	Low certainty	Studied for: Cholesterol Studied for: Blood pressure	^{29 9 14 32 22 1}
Metabolism Weight	Biological association	Low certainty	Studied for: Body weight Studied for: Blood sugar in type 2 diabetes	^{16 32 3}
Cellular	Biological association	Not enough evidence	Studied for: Cancer risk	^{6 32}

C. Body parts and organs

Connected to	Kind of connection	Evidence status	Context	Studies
Liver	Adverse effect or risk	Low certainty	Rare liver injury, mostly with extract; case reports and trials of high-dose EGCG. Preparation or compound: Concentrated green tea extract; rarely tea	^{20 5 21}

E. Health conditions

Connected to	Kind of connection	Evidence status	Context	Studies
Pregnancy	Contraindication	Low certainty	Counts toward the caffeine limit. Preparation or compound: Green tea (caffeine)	^{33 32 8 27}
Iron-deficiency anemia	Adverse effect or risk	Very low certainty	Tea can lower iron absorption; one case report. Preparation or compound: Green tea drink	^{13 10}

I. Biomarkers

Connected to	Kind of connection	Evidence status	Context	Studies
Choice reaction time	Biological association	Low certainty	Measured in trials: improved. A lab change is not the same as a health benefit.	⁷
Theanine in the dry leaf	Biological association	Moderate certainty	Measured in trials: measured. A lab change is not the same as a health benefit.	²⁷
LDL cholesterol	Biological association	Low certainty	Measured in trials: lowered. A lab change is not the same as a health benefit.	^{29 14 9}
Systolic blood pressure	Biological association	Low certainty	Measured in trials: lowered. A lab change is not the same as a health benefit.	^{22 14 9}
Body weight	Biological association	Low certainty	Measured in trials: unchanged. A lab change is not the same as a health benefit.	¹⁶
Death from any cause	Biological association	Low certainty	Measured in trials: lowered. A lab change is not the same as a health benefit.	¹
HbA1c	Biological association	Evidence against	Measured in trials: unchanged. A lab change is not the same as a health benefit.	³

J. Genes, receptors and enzymes

Connected to	Kind of connection	Evidence status	Context	Studies
UGT1A4	Preliminary mechanism	Human	Genotype linked with liver enzyme rises on high-dose extract in one secondary analysis.	²
COMT	Preliminary mechanism	Human	Genotype examined with liver enzyme changes on high-dose extract.	²

L. Active compounds

Connected to	Kind of connection	Evidence status	Context	Studies
Caffeine	Adverse effect or risk	Moderate certainty	Counts toward daily caffeine; see FDA and NHS figures. Gyokuro leaf had the most caffeine of eight Japanese green teas in a lab study; counts toward daily caffeine. Preparation or compound: Green tea	^{31 33 27}
Epigallocatechin gallate (EGCG)	Biological association	Human	Liver effects at high supplement doses; other actions not established in the sources read. Preparation or compound: Leaf	^{36 5 24 27}
Caffeine	Biological association	Human	Stimulant; see Safety tab. Preparation or compound: Leaf	^{37 31 27}
L-theanine	Biological association	Human	Reviewers link benefits for attention to caffeine and L-theanine together. Preparation or compound: Leaf	^{38 18 19 27 28}
Tannins and other polyphenols	Biological association	Human	Tea polyphenols lower iron absorption (radio-iron study, black and herb teas). Preparation or compound: Leaf and stem	^{19 13}
Arginine	Biological association	Lab measurement	Proposed with theanine to reduce stress in the authors' framework; not shown in people. Preparation or compound: Leaf	²⁷

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 3 lab markers

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

Metabolic1 Other2

The evidence

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

Evidence by outcome

Alertness and attention 4 studies Low certainty Stress and mood 5 studies · 30 people in trials Low certainty Sleep quality 1 study · 30 people in trials Very low certainty Cholesterol 4 studies Low certainty Blood pressure 3 studies Low certainty Body weight 2 studies Low certainty Heart disease and death rates in drinkers 2 studies Low certainty Cancer risk 2 studies Not enough evidence Dementia and memory loss risk 1 study Very low certainty Blood sugar in type 2 diabetes 1 study Evidence against

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 and read the abstracts of about 28 sources, read the open-access full text of the 2025 Japanese green tea composition paper for its leaf and infusion tables, read the NCCIH, FDA, NHS and EMA pages and the IARC press release for the green tea page the same day, re-read the EFSA abstract, checked the plant name in GBIF and three compounds in PubChem, and looked for LiverTox and LactMed (summary records read; the full LiverTox page was not opened). Only abstracts were read for most papers. Certainty ratings are the compiler's own reading. One theanine trial was funded by the supplement maker. No study is cited that we could not verify.

Study library: every study we checked 38

Design Research type Year from Search

Study	Design	People	Product, dose, length	Result
Abe 2019 Green tea consumption and mortality in Japanese men and women: a pooled analysis of eight population-based cohort studies in Japan European Journal of Epidemiology · PMID 31392470 · DOI	Pooled cohort	313381 313,381 Japanese adults in eight cohorts; 52,943 deaths over a mean 17.3 years	Green tea drinking (self-reported) leaf (drink) Five or more cups a day versus less than one Mean follow-up 17.3 years · vs Drinking less than 1 cup a day	Five or more cups a day versus less than one: all-cause death HR 0.90 (95% CI 0.87 to 0.94) in men and 0.82 (0.74 to 0.90) in women; heart disease HR 0.82 (0.75 to 0.90) men, 0.75 (0.68 to 0.84) women; stroke-type (cerebrovascular) HR 0.76 (0.68 to 0.85) men, 0.78 (0.68 to 0.89) women. In women, total cancer death HR 0.89 (0.83 to 0.96) at 1 to 2 cups and 0.91 (0.85 to 0.98) at 3 to 4 cups. Lower death rates among heavy green tea drinkers (an association) (All-cause HR 0.90 (0.87, 0.94) men; 0.82 (0.74, 0.90) women) Methods, limits and funding Outcomes: Deaths from all causes, heart disease, stroke, cancer, respiratory disease Limitations: Observational: tea drinkers may differ in diet, exercise and health; Japanese data may not apply elsewhere Funding and conflicts: Not stated in the abstract Read: abstract
Acosta 2023 Hepatotoxicity with High-Dose Green Tea Extract: Effect of Catechol-O-Methyltransferase and Uridine 5-Diphospho-glucuronosyltransferase 1A4 Genotypes Journal of Dietary Supplements · PMID 36178169 · DOI	Controlled trial	1075 Postmenopausal women in the Minnesota Green Tea Trial (400 in the extract group), mean age 59.8 years	High-dose green tea extract capsules (843 mg/day EGCG) versus placebo capsules extract 843 mg/day EGCG 12 months · vs Placebo capsules	This is a secondary analysis. In the extract group, women with the UGT1A4 (rs6755571) A/C variant had larger rises in ALT (about +78% and +82% at months 6 and 9) than women with C/C (about +28% and +30%). The authors suggest this variant may be a risk factor for meaningful liver enzyme rises with 6 to 9 months of high-dose extract. Genes may affect who gets liver enzyme rises on high-dose extract (ALT change differences p<0.001 and p=0.004 (months 6 and 9)) Methods, limits and funding Outcomes: Liver enzymes by gene variant Limitations: Secondary analysis; mostly white women; extract only; not about tea Funding and conflicts: Not stated in the abstract Read: abstract
Asbaghi 2021 Effect of green tea on glycemic control in patients with type 2 diabetes mellitus: A systematic review and meta-analysis Diabetes & Metabolic Syndrome · PMID 33285391 · DOI	Meta-analysis	14 randomised trials in people with type 2 diabetes	Green tea supplementary intake Differed Differed · vs Control	Supplementary green tea had no significant effect on fasting glucose, fasting insulin, HbA1c or HOMA-IR. No significant effect found Methods, limits and funding Outcomes: Fasting glucose, fasting insulin, HbA1c, HOMA-IR Limitations: Small trials; the abstract does not say whether the trials used drink or extract; no effect found is not proof of no effect Funding and conflicts: Not stated in the abstract Read: abstract
Camfield 2014 Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis Nutrition Reviews · PMID 24946991 · DOI	Systematic review	11 randomised placebo-controlled human studies of one-off doses	L-theanine and EGCG, alone or with caffeine (isolated compounds) isolated compounds Not reported here	The reviewers found moderate effect sizes in favour of caffeine and L-theanine together in the first 2 hours after the dose for alertness and attention switching accuracy, and to a lesser extent some attention outcomes. Effect size changed more with the caffeine dose than the theanine dose, particularly in the first hour. Moderate, short-lived effect of the pair, driven partly by caffeine (not given in the abstract) Methods, limits and funding Outcomes: Alertness, calmness, contentedness, state anxiety; attention tasks Limitations: Compounds given as capsules or drinks, not a cup of tea; only the first 2 hours; abstract only was read. Funding and conflicts: Not stated in the abstract (research support, non-US government) Read: abstract
EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) 2018 Scientific opinion on the safety of green tea catechins EFSA Journal · PMID 32625874 · DOI	Regulatory opinion	Review of published studies, authority reports and submitted data	Green tea infusions, reconstituted drinks and food supplements containing catechins leaf (drink) and extract Mean EGCG intake from infusions in the EU 90 to 300 mg/day (up to 866 mg/day for high-level drinkers); supplements 5 to 1,000 mg/day	Catechins from traditionally prepared green tea infusions, and reconstituted drinks of the same composition, are in general considered safe at the intakes reported in EU countries. Rare cases of liver injury have been reported after infusions, most probably an idiosyncratic (individual) reaction. Clinical trials show that EGCG at or above 800 mg a day taken as a food supplement raised liver enzymes (serum transaminases) compared with control. Drink generally safe at usual intakes; high-dose supplements raise liver enzymes Methods, limits and funding Outcomes: Liver safety of catechins (EGCG) Limitations: Abstract only was read; the full opinion could not be opened Funding and conflicts: Regulator opinion Read: abstract
Filippini 2020 Green tea (Camellia sinensis) for the prevention of cancer Cochrane Database of Systematic Reviews · PMID 32118296 · DOI	Systematic review	142 studies: 11 randomised trials (1795 people, green tea extract versus placebo) and 131 observational studies (over 1,100,000 people)	Green tea extract in trials; drinking green tea in observational studies leaf (drink) and extract Differed Differed · vs Placebo (trials); lowest intake (cohorts)	Trials of extract (low-certainty): prostate cancer RR 0.50 (95% CI 0.18 to 1.36), gynaecological cancer RR 1.50 (0.41 to 5.48), non-melanoma skin cancer RR 1.00 (0.06 to 15.92). Observational, highest versus lowest intake: overall cancer incidence RR 0.83 (0.65 to 1.07, three studies); cancer death RR 0.99 (0.91 to 1.07, eight studies); both low-certainty. Results conflicted by study design for oesophageal, prostate and urinary cancers and leukaemia. The authors call the evidence limited and inconsistent. Extract side effects included stomach and gut problems, raised liver enzymes and, more rarely, insomnia, raised blood pressure and skin reactions. No clear effect on cancer risk; inconsistent (Prostate RR 0.50 (0.18, 1.36); cancer incidence RR 0.83 (0.65, 1.07); cancer mortality RR 0.99 (0.91, 1.07)) Methods, limits and funding Outcomes: Cancer incidence and death, adverse effects, quality of life Limitations: Most studies in Asian populations who drink a lot of green tea; observational studies cannot prove cause; trials used extract Funding and conflicts: Non-US government support listed in PubMed record Read: abstract
Gerolymos 2026 Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials Molecular Psychiatry · PMID 42410082 · DOI	Systematic review	1168 31 randomised trials of oral L-theanine against placebo in healthy and clinical groups	L-theanine taken by mouth (a supplement, not tea) isolated compound Not reported here	A single dose of L-theanine improved choice reaction time (SMD 0.51, 95% CI 0.25 to 0.77), read by the authors as better attention. The drop in acute stress was modest (SMD 0.31) and largely driven by studies at high risk of bias. Fatigue did not change. After removing one outlier, depressive symptoms fell after a single dose in healthy people (SMD 0.69, 95% CI 0.13 to 1.25). Anxiety effects were inconsistent and not significant apart from one study in psychotic anxiety. No serious adverse events were reported. Short-term attention benefit; modest, biased stress result (SMD 0.51 (0.25 to 0.77) reaction time; SMD 0.31 acute stress) Methods, limits and funding Outcomes: Acute stress, anxiety, depressive symptoms, fatigue, reaction time and attention, dropouts Limitations: Tests isolated L-theanine, not gyokuro; one outlier removed for the depression result; many trials were small. Abstract only was read. Funding and conflicts: One author founded a company selling dietary supplements (stated in the record) Read: abstract
Greenwood 2014 Caffeine intake during pregnancy and adverse birth outcomes: a systematic review and dose-response meta-analysis European Journal of Epidemiology · PMID 25179792 · DOI	Systematic review	60 publications from 53 cohort and case-control studies	Caffeine from all dietary sources Not reported here	Greater caffeine intake was associated with more spontaneous abortion, stillbirth, low birth weight and small-for-gestational-age babies, but not preterm delivery. The risk per increment of caffeine was 14% higher for spontaneous abortion (95% CI 10 to 19%) and 19% for stillbirth (5 to 35%); the abstract prints the increment as 100 g, which is presumably a typo. The authors found no identifiable threshold below which the associations are absent, but say the associations are modest within usual intake and may be explained by bias, and that maintaining current recommendations is a wise precaution. Higher caffeine goes with higher risk; no safe threshold identified (see results) Methods, limits and funding Outcomes: Spontaneous abortion, stillbirth, preterm delivery, low birth weight, small for gestational age Limitations: Observational studies with large differences between them and signs of publication bias; cannot prove cause. Funding and conflicts: Research support, non-US government Read: abstract
Hartley 2013 Green and black tea for the primary prevention of cardiovascular disease Cochrane Database of Systematic Reviews · PMID 23780706 · DOI	Systematic review	821 11 randomised trials of at least 3 months in healthy adults or adults at high risk of heart disease; 7 trials tested green tea, 4 black tea	Green tea, black tea or tea extracts (doses and forms differed between trials) leaf (drink) and extracts Differed between trials At least 3 months · vs No intervention, placebo or minimal intervention	No trial reported heart or blood vessel events. Green tea: total cholesterol -0.62 mmol/L (95% CI -0.77 to -0.46), LDL cholesterol -0.64 mmol/L (-0.77 to -0.52), systolic blood pressure -3.18 mmHg (-5.25 to -1.11), diastolic -3.42 (-4.54 to -2.30). The authors say only a small number of studies contributed and the green tea results were not stable to sensitivity analysis. Adverse events in five trials were judged unlikely to be due to the tea. Small lowering of cholesterol and blood pressure, unstable (TC MD -0.62 (-0.77, -0.46); LDL MD -0.64 (-0.77, -0.52); SBP MD -3.18 (-5.25, -1.11)) Methods, limits and funding Outcomes: Heart disease events, blood pressure, cholesterol Limitations: Few trials per analysis, risk of bias, forms and doses mixed (drink and extract); no long-term follow-up Funding and conflicts: Non-US government support listed in PubMed record; no industry funding stated in the abstract Read: abstract
He 2024 Severe iron-deficiency anemia after short-term moderate consumption of green tea in woman: A rare case report Heliyon · PMID 39263133 · DOI	Case report	1 One woman who drank moderate amounts of green tea for about three months	Green tea drink leaf (drink) Moderate (amount not given in the abstract) About 3 months	Haemoglobin fell by 6.9 g/dl with severe iron-deficiency anemia. After she changed her tea habits there was no recurrence. The authors say clinicians should know even moderate tea intake can cause severe anemia in people who are especially vulnerable to its effect on iron absorption. One reported case of severe anemia Methods, limits and funding Outcomes: Haemoglobin Limitations: Single case; other causes of iron loss are not described in the abstract Funding and conflicts: Not stated Read: abstract
Hidese 2019 Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial Nutrients · PMID 31623400 · DOI	Controlled trial	30 30 healthy adults (9 men, 21 women), mean age 48.3 years, no major psychiatric illness	L-theanine tablets (a supplement, not tea) against placebo tablets, crossover isolated compound Not reported here 4 weeks · vs Placebo tablets	Self-rated depression and trait anxiety scores and the sleep quality score fell after L-theanine compared with placebo (p = 0.019, 0.006 and 0.013). Verbal fluency and executive function scores improved (p = 0.001 and 0.031). Small improvements in mood, sleep and some thinking tests (p values only; no confidence intervals in the abstract) Methods, limits and funding Outcomes: Depression, trait anxiety and sleep scores; verbal fluency and executive function Limitations: Only 30 people, 4 weeks, one supplement. Not gyokuro tea. Funding and conflicts: Funded by Taiyo Kagaku Co., Ltd.; two authors are employees of that company, which supplied the product (industry-linked) Read: abstract
Hu 2018 The safety of green tea and green tea extract consumption in adults - Results of a systematic review Regulatory Toxicology and Pharmacology · PMID 29580974 · DOI	Systematic review	Toxicology studies and adverse-event data from 159 human intervention studies	Brewed green tea, green tea in drinks or food, and concentrated catechin-rich preparations leaf (drink) and extract	Liver was the target organ. Liver adverse events in humans came from a limited range of concentrated, catechin-rich preparations taken as large single doses, and not from brewed tea or extracts used in drinks or food. The authors derived a safe intake level for adults for solid single-dose preparations and a separate, higher observed safe level for beverage forms (the numbers are in the paper). Liver effects tied to concentrated bolus-dose preparations, not brewed tea Methods, limits and funding Outcomes: Liver adverse events Limitations: Abstract only was read; the abstract does not state who funded the review Funding and conflicts: Funding and conflict-of-interest statement not read Read: abstract
Hurrell 1999 Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages British Journal of Nutrition · PMID 10999016	Controlled trial	Adult volunteers given a bread meal with radio-labelled iron	Black tea, herb teas (chamomile, vervain, lime flower, pennyroyal, peppermint), coffee and cocoa leaf (drink) Test beverages with different polyphenol amounts Single meals · vs Water control meal	All the beverages reduced iron absorption in a way that depended on their polyphenol content. Black tea cut absorption by 79 to 94 percent, peppermint tea 84, pennyroyal 73, cocoa 71, vervain 59, lime flower 52 and camomile 47 percent. Milk made little difference. Green tea was NOT tested. Large drop in iron absorption from a meal Methods, limits and funding Outcomes: Iron absorption from the meal Limitations: Green tea not tested; single meals in adults; applying this to green tea is an inference Funding and conflicts: Non-US government support listed in PubMed record Read: abstract
Igho-Osagie 2020 Short-Term Tea Consumption Is Not Associated with a Reduction in Blood Lipids or Pressure: A Systematic Review and Meta-Analysis of Randomized Controlled Trials Journal of Nutrition · PMID 33188386 · DOI	Meta-analysis	798 14 randomised trials in healthy adults and at-risk adults (obesity, prediabetes, borderline high cholesterol, metabolic syndrome)	Green tea or black tea leaf (drink) Differed 4 to 24 weeks (mean 7.4) · vs Placebo or control	No significant effect of tea on systolic or diastolic blood pressure, total, LDL or HDL cholesterol or triglycerides. Strength of evidence was low to moderate because the studies were small and underpowered. No significant effect in short trials (No significant effects (intervals not given in the abstract)) Methods, limits and funding Outcomes: Blood pressure, total, LDL and HDL cholesterol, triglycerides Limitations: Small trials, short duration, green and black tea pooled; absence of effect is not proof of no effect Funding and conflicts: Non-US government support listed in PubMed record Read: abstract
Jayasingha 2025 Fluoride in tea: accumulation, dietary exposure, and future strategies for risk mitigation in food safety; a scoping review Critical Reviews in Food Science and Nutrition · PMID 40504749 · DOI	Scoping review lab/food analysis	88 studies worldwide on fluoride in tea	Tea (all types) leaf (drink)	Tea plants take up fluoride from soil. Longer brewing released more fluoride. Average levels by type were brick tea 4.78 mg/L, black tea 2.73, green tea 1.37, white tea 0.49 and herbal tea 0.17. The review says black tea poses risks for children and for adults in high-intake regions; excessive intake may cause tooth and bone fluorosis and kidney disease. Green tea has less fluoride than black or brick tea but more than white or herbal tea Methods, limits and funding Outcomes: Fluoride in brewed tea Limitations: Scoping review; averages mix many countries; local water also adds fluoride Funding and conflicts: Not stated Read: abstract
Jurgens 2012 Green tea for weight loss and weight maintenance in overweight or obese adults Cochrane Database of Systematic Reviews · PMID 23235664 · DOI	Systematic review	Randomised trials of at least 12 weeks in overweight or obese adults; six trials outside Japan (532 people) and eight in Japan (1030 people)	Green tea preparations (drink and extracts) leaf (drink) and extracts Differed 12 to 13 weeks · vs Control	Outside Japan: weight difference -0.04 kg (95% CI -0.5 to 0.4), BMI -0.2 kg/m2 (-0.5 to 0.1), waist -0.2 cm (-1.4 to 0.9). The eight Japanese trials were too different to pool; weight differences ranged from -0.2 to -3.5 kg. Adverse events in four of eight trials that recorded them were mild to moderate; two needing hospital care were reported as not related. Almost no weight change outside Japan; mixed results in Japanese trials (Weight MD -0.04 kg (-0.5, 0.4) outside Japan) Methods, limits and funding Outcomes: Weight, BMI, waist circumference, adverse events Limitations: Short trials; green tea preparations of many kinds; not a drink-only result Funding and conflicts: Non-US government support listed in PubMed record Read: abstract
Kakutani 2019 Green Tea Intake and Risks for Dementia, Alzheimer's Disease, Mild Cognitive Impairment, and Cognitive Impairment: A Systematic Review Nutrients · PMID 31137655 · DOI	Systematic review	3 cohort studies and 5 cross-sectional studies	Green tea drinking leaf (drink) · vs Lower or no intake	One cohort and three cross-sectional studies supported a benefit, one cohort and one cross-sectional partly supported it, and one cohort and one cross-sectional found no association. The authors say well-designed cohort studies are needed. Mixed observational results Methods, limits and funding Outcomes: Dementia, Alzheimer disease, mild cognitive impairment, cognitive impairment Limitations: Observational only; small number of studies; cannot show cause Funding and conflicts: Not stated in the abstract Read: abstract
Mancini 2017 Green tea effects on cognition, mood and human brain function: A systematic review Phytomedicine · PMID 28899506 · DOI	Systematic review	21 studies: 4 randomised trials, 12 crossover studies, 4 cross-sectional studies and 1 cohort	Green tea, green tea extract, L-theanine or EGCG leaf (drink), extract and isolated compounds Differed Differed · vs Differed	The reviewers found evidence that green tea influences psychological symptoms (for example less anxiety), cognition (for example memory and attention) and brain function (for example working-memory activation on brain scans). Benefits on cognition were seen with caffeine and L-theanine together, with less effect from either alone, so the effect cannot be put down to one ingredient. Possible small effects on attention and memory Methods, limits and funding Outcomes: Anxiety and mood, memory and attention, brain activity Limitations: Mixes drink, extract and isolated compounds; many short or single-dose studies; PubMed only; quality scores are the reviewers own Funding and conflicts: Not stated in the abstract Read: abstract
NICHD / 2006 Drugs and Lactation Database (LactMed): Green Tea LactMed (NCBI Bookshelf) · PMID 30000907	Database record	n/a	Green tea leaves and stems leaf and stem	Green tea leaves and stems contain caffeine, L-theanine, polyphenols and tannins. Fussiness, jitteriness and poor sleep have been reported in infants of mothers with extremely high caffeine intakes. Giving tea directly to infants can interfere with iron absorption and cause anemia, but anemia in breastfed infants has not been reported with maternal tea intake. Passage of L-theanine into breastmilk has not been studied. No studies of oral green tea extract in breastfeeding were found. No clear harm from usual maternal tea intake; caution at very high caffeine Methods, limits and funding Outcomes: Breastfeeding safety Limitations: Summary record; no new data Funding and conflicts: Public database Read: abstract
NIDDK 2012 LiverTox: Green Tea (Clinical and Research Information on Drug-Induced Liver Injury) LiverTox (NCBI Bookshelf) · PMID 31643260	Database record	n/a	Green tea extract and, more rarely, large amounts of green tea leaf and extract	Green tea extract and, more rarely, ingestion of large amounts of green tea have been implicated in cases of clinically apparent acute liver injury, including instances of acute liver failure and either need for urgent liver transplantation or death. Rare but serious liver injury, mostly with extract Methods, limits and funding Outcomes: Drug-induced liver injury Limitations: Only the PubMed summary was read; the full LiverTox page was not opened Funding and conflicts: Public database Read: abstract
Pillukat 2014 Concentrated green tea extract induces severe acute hepatitis in a 63-year-old woman - a case report with pharmaceutical analysis Journal of Ethnopharmacology · PMID 24862489 · DOI	Case report	1 A 63-year-old woman taking green tea capsules on the advice of a cancer support group	Concentrated green tea extract capsules (EGCG 93.2% of the catechins found) extract Very high EGCG dose level per the analysis	Severe hepatitis assessed as probably caused by the capsules (CIOMS/RUCAM score). The liver tissue pattern fit drug-induced hepatitis and other causes were excluded. After stopping, and a treatment called albumin dialysis, she recovered quickly and fully. Lab analysis of the capsules found no contaminants. Severe but reversible liver injury linked to concentrated extract Methods, limits and funding Outcomes: Liver injury Limitations: Single case; extract, not brewed tea Funding and conflicts: Not stated Read: abstract
Rezaei 2025 Effect of green tea supplementation on blood pressure in adults: a GRADE-assessed systematic review and dose-response meta-analysis of randomised controlled trials Blood Pressure · PMID 40497293 · DOI	Meta-analysis	36 randomised trials in adults	Green tea supplementation (forms not broken out in the abstract) Not given here Studies of 8 weeks or less showed stronger effects · vs Control or placebo	Systolic blood pressure fell by 1.08 mmHg (95% CI -1.98 to -0.18; I2 85%) and diastolic by 1.09 mmHg (-1.67 to -0.50; I2 74%). Effects were stronger in people with raised starting blood pressure, shorter studies, Asian populations and women. No clear link between size of change and dose or duration. The authors call green tea a complementary approach, not a treatment. Very small average blood pressure drop with large differences between studies (SBP -1.08 (-1.98, -0.18); DBP -1.09 (-1.67, -0.50)) Methods, limits and funding Outcomes: Systolic and diastolic blood pressure Limitations: Very high heterogeneity; the abstract does not separate drink from extract; the GRADE rating is not given in the abstract Funding and conflicts: Not stated in the abstract Read: abstract
Rodriguez 2020 Human exposure to fluoride from tea (Camellia sinensis) in a volcanic region - Canary Islands, Spain Environmental Science and Pollution Research · PMID 32740848 · DOI	Food analysis lab/food analysis	90 90 tea samples (Canary Islands)	Mixed, black and other teas prepared with local tap water leaf (drink) Two 250 mL cups a day assumed	Mixed teas (2.82 mg/L) and black teas (2.28 mg/L) had the highest fluoride. Two daily cups of those teas made with local tap water would give children aged 4 to 8 a large share (74.4% and 63.6%) of the EFSA upper intake level. The authors advise less tea for children and in pregnancy. Fluoride in tea can matter for young children in some regions Methods, limits and funding Outcomes: Fluoride in tea Limitations: Local water and region; green tea results are not given in the abstract Funding and conflicts: Not stated Read: abstract
Saklar 2015 Effects of different brewing conditions on catechin content and sensory acceptance in Turkish green tea infusions Journal of Food Science and Technology · PMID 26396411 · DOI	Lab analysis lab/food analysis	Turkish green tea brewed at 75, 85 and 95 C for 1 to 45 minutes; nine trained tasters	Brewed Turkish green tea leaf (drink)	Brewing at 85 C for 3 minutes gave the most EGCG (50.69 mg per 100 ml) with the best taste scores. Brewing 30 and 45 minutes at 85 and 95 C tasted bitter and dark. Catechin level and taste depend on brewing time and heat Methods, limits and funding Outcomes: Catechin content and taste Limitations: One tea, a laboratory study with nine tasters; not a rule for all green teas Funding and conflicts: Not stated Read: abstract
Taylor 1999 Probable antagonism of warfarin by green tea Annals of Pharmacotherapy · PMID 10332534 · DOI	Case report	1 A 44-year-old man with a mechanical aortic heart valve taking warfarin	Green tea drink leaf (drink) Half a gallon to a gallon of green tea a day for about a week About 1 week before the low reading	The INR fell from 3.79 to 1.37 about three weeks later, and was 1.14 a month after. He had started drinking one-half to one gallon of green tea a day about a week before the INR of 1.37. After stopping the tea the INR rose to 2.55. The authors suggested vitamin K in the tea. A drop in warfarin effect linked in time to a very large amount of green tea (INR 3.79 to 1.37) Methods, limits and funding Outcomes: Blood clotting test (INR) Limitations: One case; cannot prove cause; very large amount of tea; vitamin K content was not measured Funding and conflicts: Not stated Read: abstract
Unno 2016 Anti-stress effects of drinking green tea with lowered caffeine and enriched theanine, epigallocatechin and arginine on psychosocial stress induced adrenal hypertrophy in mice Phytomedicine · PMID 27765356 · DOI	Animal research mouse	Male mice under psychosocial stress from confrontational housing	Three green teas given as drinking water: theanine-rich gyokuro, standard sencha, and low-caffeine sencha leaf infusion in room-temperature water Not reported here	Adrenal enlargement was significantly reduced in mice that drank the theanine-rich tea and the low-caffeine tea made with room-temperature water. Caffeine and EGCG worked against the anti-stress effect of theanine, while EGC and arginine kept it. Anti-stress signal in mice only (not given in the abstract) Methods, limits and funding Outcomes: Adrenal gland enlargement as a stress marker compared with mice drinking water Limitations: Mice, not people. Gyokuro was one of three teas. Not a basis for any claim about people. Funding and conflicts: Not stated in the abstract Read: abstract
Unno 2025 Stress-Relieving Effects of Japanese Green Tea: Evaluation Using the Molar Ratio of Caffeine and Epigallocatechin Gallate to Theanine and Arginine as an Indicator Foods · PMID 39796392 · DOI	Food analysis lab analysis	Eight types of Japanese green tea bought in Japan in 2022 (gyokuro was blended from six teas from Yame, Uji and Asahina); almost all first crop	Gyokuro and seven other Japanese green teas: leaf and test infusions measured in the lab leaf and infusion Not reported here	Per gram of dry leaf, gyokuro held 30.84 mg theanine, 35.41 mg caffeine and 53.31 mg EGCG. Superior sencha held 20.37 mg theanine, 31.01 mg caffeine and 67.45 mg EGCG. The authors say gyokuro had more amino acids and caffeine than any other green tea tested and the lowest catechins apart from hojicha. In the authors' own test infusions (each tea brewed under different conditions, so not like for like) gyokuro gave about 2,807 mg/L theanine and 2,261 mg/L caffeine against about 256 and 305 mg/L for superior sencha. The authors report a CE/TA ratio of 1.28 for gyokuro leaf and 0.70 for its infusion, and say teas below 3 can be expected to have a stress-relieving effect (a ratio the same group proposed from animal and clinical work, not a result of this paper). Gyokuro leaf is high in both theanine and caffeine (none (descriptive lab measurements)) Methods, limits and funding Outcomes: Amino acids, caffeine and catechins in leaf and infusion; the CE/TA ratio (caffeine plus EGCG compared with theanine plus arginine) Limitations: Lab measurements of blended market samples, one season; no people were tested; the stress-relief link is the authors' inference. Brewing conditions differed between teas. Funding and conflicts: University of Shizuoka grant stated; the authors declare no conflicts of interest Read: abstract
Unno 2026 Compositional Diversity and Functional Interactions of Bioactive Compounds in Japanese Green Tea: Focus on Matcha, Sencha, and Gyokuro Molecules · PMID 42654013 · DOI	Narrative review review of lab and human work	Review of the make-up of Japanese green teas (matcha, sencha, gyokuro)	Matcha, sencha and gyokuro leaf Not reported here	The authors describe gyokuro as a premium shaded tea with a particularly high theanine content, like authentic matcha. They say amounts and ratios of components vary a lot with harvest season, cultivar and growing practice, and that the stress-relieving effect of theanine is shaped by caffeine and catechins that come with it. Gyokuro is high in theanine; ratios matter (none) Methods, limits and funding Outcomes: How amounts and ratios of catechins, caffeine and theanine vary and may interact Limitations: Narrative review, not a systematic search. Abstract only was read. Same research group as the 2025 composition paper. Funding and conflicts: The authors declare no conflicts of interest Read: abstract
Zheng 2011 Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials American Journal of Clinical Nutrition · PMID 21715508 · DOI	Meta-analysis	1136 14 randomised trials in adults	Green tea beverage or green tea extract leaf (drink) and extract Differed Differed · vs Control	Total cholesterol lowered by 7.20 mg/dL (95% CI -8.19 to -6.21) and LDL cholesterol by 2.19 mg/dL (-3.16 to -1.21); HDL cholesterol did not change significantly. The authors say changes were not influenced by type of intervention, dose, duration, health status or study quality. Small average drop in total and LDL cholesterol (TC -7.20 (-8.19, -6.21) mg/dL; LDL -2.19 (-3.16, -1.21) mg/dL) Methods, limits and funding Outcomes: Total, LDL and HDL cholesterol Limitations: Mixes drinks and extracts; the abstract gives no separate drink-only result; later reviews found no effect in short trials (see Igho-Osagie 2020) Funding and conflicts: Non-US government support listed in PubMed record; funding details not in the abstract Read: abstract
n/a 2016 IARC (WHO): Press release no. 244, coffee, mate and very hot beverages (15 June 2016) n/a · Source	Authoritative guidance n/a	n/a	n/a	IARC classified drinking very hot beverages as probably carcinogenic to humans (Group 2A), based on limited evidence from studies in places where tea or mate is drunk very hot, and said it is the temperature rather than the drink that appears responsible. Methods, limits and funding Outcomes: IARC classified drinking very hot beverages as probably carcinogenic to humans (Group 2A), based on limited evidence from studies in places where tea or mate is drunk very hot, and said it is the temperature rather than the drink that appears responsible. Limitations: Press release read from the PDF on 2026-10-25; the exact temperature figure could not be read from the extracted text, so it is not quoted here. Read: full-text
n/a 2024 FDA: Spilling the Beans: How Much Caffeine Is Too Much? (content current as of 28 Aug 2024) n/a · Source	Authoritative guidance n/a	n/a	n/a	Lists green tea at 37 mg caffeine per 12 fl oz drink. Cites 400 mg a day as an amount not generally linked with negative effects in most adults, with wide differences in sensitivity. Lists signs of too much caffeine (faster heart rate, palpitations, high blood pressure, insomnia, anxiety, jitters, upset stomach, nausea, headache). Says caffeinated drinks should be avoided for children younger than age 2 (quoting the Dietary Guidelines) and that pregnant or breastfeeding people should talk to a health professional. Methods, limits and funding Outcomes: Lists green tea at 37 mg caffeine per 12 fl oz drink. Cites 400 mg a day as an amount not generally linked with negative effects in most adults, with wide differences in sensitivity. Lists signs of too much caffeine (faster heart rate, palpitations, high blood pressure, insomnia, anxiety, jitters, upset stomach, nausea, headache). Says caffeinated drinks should be avoided for children younger than age 2 (quoting the Dietary Guidelines) and that pregnant or breastfeeding people should talk to a health professional. Limitations: Consumer guidance page, not a trial. Read in full on 2026-10-25. Read: full-text
n/a 2025 NCCIH (NIH): Green Tea: Usefulness and Safety (last updated February 2025) n/a · Source	Authoritative guidance n/a	n/a	n/a	Says definite conclusions cannot yet be reached on whether green tea helps for most uses. Cancer results inconsistent; lower heart disease risk seen in Asian but not Western groups; small cholesterol drops mostly from extract trials; no safety concerns reported for green tea as a drink in adults; liver injury uncommon and mostly with extract tablets or capsules; interactions with nadolol (high-dose green tea), atorvastatin (extract) and raloxifene; keep caffeine moderate in pregnancy. Methods, limits and funding Outcomes: Says definite conclusions cannot yet be reached on whether green tea helps for most uses. Cancer results inconsistent; lower heart disease risk seen in Asian but not Western groups; small cholesterol drops mostly from extract trials; no safety concerns reported for green tea as a drink in adults; liver injury uncommon and mostly with extract tablets or capsules; interactions with nadolol (high-dose green tea), atorvastatin (extract) and raloxifene; keep caffeine moderate in pregnancy. Limitations: A regulator-style fact sheet, not a trial. Page text read in full on 2026-10-25. Read: full-text
n/a 2026 NHS (UK): Foods to avoid in pregnancy (page last reviewed 15 June 2026) n/a · Source	Authoritative guidance n/a	n/a	n/a	Says you should not have more than 200 mg of caffeine a day in pregnancy, estimates about 75 mg in a cup of tea such as black or green tea, and says too much caffeine has been linked to a higher chance of miscarriage and stillbirth. Methods, limits and funding Outcomes: Says you should not have more than 200 mg of caffeine a day in pregnancy, estimates about 75 mg in a cup of tea such as black or green tea, and says too much caffeine has been linked to a higher chance of miscarriage and stillbirth. Limitations: Public-health guidance, not a trial. Read in full on 2026-10-25. The per-cup figure is an estimate. Read: full-text
n/a 2026 EMA: Camelliae sinensis non fermentatum folium (green tea), herbal medicinal product page n/a · Source	Authoritative guidance n/a	n/a	n/a	Page lists Camellia sinensis (L.) Kuntze, non fermentatum folium (green tea), therapeutic area "Fatigue and weakness", status "Assessment finalised", outcome "European Union herbal monograph". Documents: final EU herbal monograph (EMA/HMPC/283630/2012, published 29 April 2014), assessment report and an addendum to the assessment report (EMA/HMPC/30571/2022, published 26 September 2022). Methods, limits and funding Outcomes: Page lists Camellia sinensis (L.) Kuntze, non fermentatum folium (green tea), therapeutic area "Fatigue and weakness", status "Assessment finalised", outcome "European Union herbal monograph". Documents: final EU herbal monograph (EMA/HMPC/283630/2012, published 29 April 2014), assessment report and an addendum to the assessment report (EMA/HMPC/30571/2022, published 26 September 2022). Limitations: Only the web page was read. The monograph and assessment-report PDFs were not opened, so the wording of the monograph is NOT verified. Read: abstract
n/a 2026 GBIF Backbone Taxonomy: Camellia sinensis (L.) Kuntze (usage key 3189635), retrieved 2026-10-25 n/a · Source	Database record n/a	n/a	n/a	Accepted species, family Theaceae, order Ericales, genus Camellia. Synonyms listed by the API include Camellia bohea (L.) Sweet, Camellia chinensis (Sims) Kuntze and Camellia cantonensis Lour. Methods, limits and funding Outcomes: Accepted species, family Theaceae, order Ericales, genus Camellia. Synonyms listed by the API include Camellia bohea (L.) Sweet, Camellia chinensis (Sims) Kuntze and Camellia cantonensis Lour. Limitations: Taxonomic database record via the GBIF API. Read: full-text
n/a 2026 PubChem: epigallocatechin gallate (CID 65064), formula C22H18O11 n/a · Source	Database record n/a	n/a	n/a	Compound record confirmed through the PubChem API on 2026-10-25. Methods, limits and funding Outcomes: Compound record confirmed through the PubChem API on 2026-10-25. Limitations: Database record only. Read: full-text
n/a 2026 PubChem: caffeine (CID 2519), formula C8H10N4O2 n/a · Source	Database record n/a	n/a	n/a	Compound record confirmed through the PubChem API on 2026-10-25. Methods, limits and funding Outcomes: Compound record confirmed through the PubChem API on 2026-10-25. Limitations: Database record only. Read: full-text
n/a 2026 PubChem: L-theanine (CID 439378), formula C7H14N2O3 n/a · Source	Database record n/a	n/a	n/a	Compound record confirmed through the PubChem API on 2026-10-25. Methods, limits and funding Outcomes: Compound record confirmed through the PubChem API on 2026-10-25. Limitations: Database record only. Read: full-text

What we do not know yet

What the evidence supports: a short-term attention effect of caffeine plus theanine as compounds; low-certainty small effects of green tea in general on cholesterol and blood pressure.
No trial of gyokuro tea in people for any outcome.
No measured lead, cadmium, aluminium or pesticide values for gyokuro were found.
The caffeine in a cup of gyokuro was only measured in lab test infusions; official cup figures are for ordinary green tea.
The EMA monograph and LiverTox full text were not opened.

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. New publications never change ratings automatically.

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".

Metabolic 3

▼

LDL cholesterol

Lowered in trials

The cholesterol carried in the blood that is linked with higher heart disease risk.

Low certainty

Results and what it means

Why it was measured

To see whether green tea changes blood fats.

Statistical vs. clinical meaning

Small and inconsistent; a lab number, not a heart outcome.

Safety implication

None from the numbers; see the Safety tab for extract risks.

Study	Result	People	Product
²⁹	LDL -2.19 mg/dL (95% CI -3.16 to -1.21)	Adults in 14 trials	Green tea drinks or extracts
¹⁴	No significant change in LDL	798 people in 14 trials	Green or black tea, 4 to 24 weeks

^{29 14 9}

●

Body weight

Unchanged in trials

Weight in kilograms.

Low certainty

Results and what it means

Why it was measured

To see whether green tea helps with weight loss.

Statistical vs. clinical meaning

No meaningful change outside Japan.

Safety implication

None.

Study	Result	People	Product
¹⁶	-0.04 kg (95% CI -0.5 to 0.4) outside Japan; -0.2 to -3.5 kg in Japanese trials, not pooled	Overweight adults, 12 to 13 weeks	Green tea preparations

¹⁶

●

HbA1c

Unchanged in trials

A blood test that shows average blood sugar over about three months.

Evidence against

Results and what it means

Why it was measured

To see whether green tea helps people with type 2 diabetes.

Statistical vs. clinical meaning

No effect found.

Safety implication

None.

Study	Result	People	Product
³	No significant effect on HbA1c, fasting glucose, insulin or HOMA-IR	14 trials in type 2 diabetes	Green tea supplementation

Other 4

●

Choice reaction time

Improved in trials

How fast a person picks the right response in a computer task. Faster is read as better attention.

Low certainty

Results and what it means

Why it was measured

To see whether theanine sharpens attention.

Statistical vs. clinical meaning

A short-term lab-test change for a supplement, not gyokuro tea.

Safety implication

None reported; no serious adverse events in the review.

Study	Result	People	Product
⁷	SMD 0.51 (95% CI 0.25 to 0.77) after a single theanine dose	Adults in randomised trials	Oral L-theanine supplement

⁷

●

Theanine in the dry leaf

Measured in trials

The amount of the amino acid theanine in a gram of dry tea leaf, measured in a lab.

Moderate certainty

Results and what it means

Why it was measured

Shaded tea is said to be richer in it.

Statistical vs. clinical meaning

A measurement of what is in the leaf, not an effect in a person.

Safety implication

None.

Study	Result	People	Product
²⁷	Gyokuro 30.84 mg per g; superior sencha 20.37; standard sencha 18.91	Blended market samples, Japan, 2022	Dry leaf, lab analysis

²⁷

▼

Systolic blood pressure

Lowered in trials

The top number in a blood pressure reading.

Low certainty

Results and what it means

Why it was measured

To see whether green tea changes blood pressure.

Statistical vs. clinical meaning

Very small and varied.

Safety implication

None from the numbers.

Study	Result	People	Product
²²	-1.08 mmHg (95% CI -1.98 to -0.18)	36 trials in adults	Green tea supplementation
¹⁴	No significant change	798 people in 14 trials	Green or black tea, 4 to 24 weeks

^{22 14 9}

▼

Death from any cause

Lowered in trials

The risk of dying from any cause during follow-up.

Low certainty

Results and what it means

Why it was measured

To see whether heavy green tea drinkers live longer.

Statistical vs. clinical meaning

Observational association only.

Safety implication

None.

Study	Result	People	Product
¹	HR 0.90 (0.87 to 0.94) men; 0.82 (0.74 to 0.90) women, 5+ cups a day versus under 1	313,381 Japanese adults	Self-reported green tea drinking

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 8

Gyokuro is a high-caffeine tea. In a Japanese lab study, dry gyokuro leaf held 35.41 mg of caffeine per gram, the most of eight Japanese green teas, with 24.70 to 31.01 mg per gram in the sencha types. In the authors' own test infusions, gyokuro (made with much more leaf in much less water) reached about 2,261 mg/L of caffeine against about 305 mg/L for a superior sencha. Their brewing conditions differed by tea, so these are not like-for-like, but they show a gyokuro cup can be far stronger than a standard green tea cup. The FDA and NHS figures for a cup of green tea (37 mg and about 75 mg) are averages for ordinary green tea, not measurements of gyokuro. Count it carefully if you limit caffeine. Food analysis ^{27 31 33}
A cup of tea and a green tea extract capsule are not the same thing. NCCIH reports no safety concerns for green tea (in general, not gyokuro specifically) drunk as a beverage by adults, apart from its caffeine. Liver injury is uncommon but has been reported, mostly with concentrated extract in tablets or capsules. EFSA judged traditionally prepared green tea infusions generally safe at the intakes seen in Europe, and found that high-dose EGCG supplements raised liver enzymes in trials. Do not carry safety or benefit results from one form to the other. Authoritative guidance ^{32 5 12}
Rare liver injury, mostly with extract. LiverTox says green tea extract, and more rarely large amounts of green tea, have been linked to clinically apparent liver injury, including liver failure needing transplant or ending in death. EFSA noted rare cases after infusions too, probably an individual reaction. A case report describes severe hepatitis from concentrated extract capsules that cleared after stopping them. Anyone with liver disease, or who has had liver trouble from a supplement, should ask a clinician before any extract. Case report ^{20 5 21}
Caffeine. Green tea contains caffeine. The FDA lists 37 mg in a 12 fl oz drink and says about 400 mg a day is not generally linked with harm in most adults, with wide differences in sensitivity. Too much can cause fast heartbeat, palpitations, high blood pressure, poor sleep, anxiety, jitters, upset stomach, nausea and headache. Gyokuro is higher in caffeine than other Japanese green teas measured, so caffeine effects may come on faster than with a usual cup of tea. Authoritative guidance ^{31 27}
Pregnancy, breastfeeding and young children. The NHS says not to have more than 200 mg of caffeine a day in pregnancy and counts about 75 mg in a cup of black or green tea. NCCIH says to keep caffeine moderate in pregnancy and to ask your provider. LactMed reports fussiness, jitteriness and poor sleep in infants only with extremely high maternal caffeine, and says tea given directly to infants can interfere with iron absorption and cause anemia. The FDA quotes the Dietary Guidelines that caffeinated drinks should be avoided for children younger than age 2. A 2014 meta-analysis of 53 observational studies linked higher caffeine intake with more miscarriage, stillbirth and low birth weight and found no threshold below which the links disappear, while saying the links are modest within usual intake and may be partly bias. The NHS limit is the current UK advice. Authoritative guidance ^{33 32 19 31 8}
Iron. Polyphenols in tea cut iron absorption from a meal in a radio-iron study, but that study did not test green tea. A 2024 case report describes severe iron-deficiency anemia in a woman after about three months of moderate green tea. If you have low iron or anemia, ask a clinician about tea around meals. Human study ^{13 10}
Medicines. NCCIH says high doses of green tea lowered blood levels of the heart medicine nadolol, green tea extract lowered levels of atorvastatin, and an NCCIH-funded study showed an interaction with raloxifene. One 1999 case report links very large amounts of green tea with weaker warfarin effect. Ask your pharmacist if you take any regular medicine. Authoritative guidance ^{32 25}
Very hot drinks. IARC classed drinking very hot beverages as probably carcinogenic to humans (Group 2A) for oesophageal cancer and said it is the temperature, not the drink, that appears responsible. This applies to hot tea as to any other very hot drink; letting a cup cool is a sensible step. Authoritative guidance ³⁰

Side effects 6

Effect	How often	Severity and recovery	Evidence
Caffeine effects (fast heartbeat, jitters, poor sleep, upset stomach) Listed by the FDA as signs of too much caffeine from any source. Gyokuro measured higher in caffeine than sencha in a lab study.	Depends on how much caffeine you take and how sensitive you are; no rate in the sources read	mild to moderate Reversible when caffeine is cut back	Authoritative guidance ^{31 27}
Nausea, constipation, stomach discomfort and higher blood pressure (extract) NCCIH lists these for green tea extract supplements.	No rate in the sources read	mild Reversible after stopping (not stated)	Authoritative guidance ³²
Gut problems, raised liver enzymes, insomnia, raised blood pressure, skin reactions (extract) Cochrane lists these as adverse effects of green tea extract in trials.	Not given in the abstract	mild to moderate Not given	Systematic review ⁶
Liver injury (mostly extract; rarely tea) High-dose extract raised liver enzymes in trials (EFSA, abstract).	Uncommon; no rate found	severe Mostly recovery after stopping; some cases need transplant or are fatal	Case report ^{32 20 21 5}
Lower iron absorption; anemia in a vulnerable person Green tea was not tested in the radio-iron study.	One case report	moderate to severe Improved after changing tea habits	Case report ^{13 10}
Fluoride intake from tea Green tea averaged 1.37 mg/L in a scoping review, below black and brick tea; the risk discussed is mainly for children and heavy drinkers.	Depends on tea type, brewing time and local water	not stated not stated	Food analysis ^{15 23}

Liver

Liver injury linked to green tea is rare and mostly linked to concentrated extract capsules or tablets. LiverTox says extract, and more rarely very large amounts of tea, have been implicated in acute liver injury, including liver failure needing transplant or death. EFSA found raised liver enzymes with high-dose EGCG supplements in trials and noted rare liver injury after infusions, most probably an unusual individual reaction. A systematic review of 159 human studies found liver events came from concentrated, catechin-rich preparations taken in large single doses, not from brewed tea or extracts used in drinks or food. NCCIH says people with a specific immune-related gene variant seem especially susceptible, and a secondary analysis of a one-year extract trial found liver enzyme rises differed by gene variant. ^{20 5 12 21 2 32}

How often. No rate in tea drinkers or extract users could be found in the sources read.

Monitoring. No monitoring advice was read from an agency. The Safety tab tells readers to stop extract and seek care if liver warning signs appear.

p24862489.

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

Medicines and supplements 6

With	Why it matters	Importance	Evidence	What to do
Warfarin prescription	The case authors suggested vitamin K in the tea could counter warfarin; vitamin K was not measured.	One 1999 case report: INR fell from 3.79 to 1.37 after about a week of half a gallon to a gallon of green tea a day, and rose to 2.55 after stopping. It cannot prove cause and the amount was very large.	Case report Very low certainty ²⁵	Tell your prescriber about any big change in tea habits so your INR can be checked.
Nadolol (beta-blocker) prescription	Not described in the source read.	NCCIH says green tea at high doses reduced blood levels of nadolol and so its effectiveness.	Authoritative guidance Low certainty ³²	Ask your pharmacist if you take nadolol.
Atorvastatin (cholesterol medicine) prescription	Not described in the source read.	NCCIH says green tea extract can reduce blood levels of atorvastatin. This is about the extract.	Authoritative guidance Low certainty ³²	Ask your pharmacist before taking green tea extract with a statin.
Raloxifene (bone medicine) prescription	Not described in the source read.	NCCIH says a study it funded showed an interaction between green tea and raloxifene. Details were not given.	Authoritative guidance Low certainty ³²	Ask your pharmacist.
Iron supplements and iron-poor diets supplement	Tea polyphenols reduce iron absorption in general.	A radio-iron study showed black tea and herb teas cut iron absorption; green tea was not tested, and one case report links moderate green tea with severe anemia.	Human study Low certainty ^{13 10}	If you have low iron, ask a clinician about drinking tea away from meals. Whether that works was not tested in the sources read.
Other sources of caffeine food	Caffeine adds up across coffee, other teas, energy drinks and some supplements.	The FDA says its 400 mg figure is for all caffeine in a day.	Authoritative guidance Moderate certainty ^{31 33}	Count all caffeine sources, especially in pregnancy.

Who should check first 6

Situation	Advice	Evidence
Pregnancy	Gyokuro is not banned in pregnancy, but it carries a lot of caffeine and counts toward the daily limit (the NHS says no more than 200 mg a day). Ask your midwife or doctor how to count it. No source read covers green tea extract capsules in pregnancy, so ask a clinician before using them.	Authoritative guidance ^{33 32 8 27}
Breastfeeding	LactMed reports infant fussiness and poor sleep only with extremely high maternal caffeine. No studies of green tea extract in breastfeeding were found.	Authoritative guidance ¹⁹
Infants and young children	Do not give tea to infants. LactMed says it can interfere with iron absorption and cause anemia. Avoid caffeinated drinks for children under 2 (FDA, quoting the Dietary Guidelines).	Authoritative guidance ^{19 31}
Liver disease or past liver injury from a supplement	Ask a clinician before using green tea extract capsules or tablets, because of the liver injury reports. The sources read do not give a rule for brewed tea in liver disease.	Precaution from liver reports ^{20 5}
Low iron or anemia	Ask a clinician. Tea can lower iron absorption.	Human study ^{13 10}
Taking warfarin, nadolol, a statin or raloxifene	Ask your pharmacist or prescriber before changing how much green tea or extract you take.	Authoritative guidance ^{25 32}

Overdose, product quality and regulators

Summary. Brewed green tea has no safety concerns reported for adults (NCCIH), apart from caffeine. The main toxicity concern is the liver, linked to concentrated catechin-rich extract taken in large single doses. No toxicity data specific to gyokuro were found.

Animal. The Hu systematic review says lab studies show the liver as target organ, strongly tied to dosing conditions such as a large single dose by gavage and fasting, and to total catechin and EGCG content.

Human doses studied. EFSA found that high-dose EGCG taken as a food supplement raised liver enzymes in trials (the threshold is in the opinion). The Minnesota Green Tea Trial gave a high-dose extract for 12 months.

High dose or long term signals. Liver enzyme rises with long high-dose extract use; differences by gene variant in one secondary analysis.

Overdose response. Not described in the sources read.

Genotoxicity. Not read.

Toxic or hazardous parts. Leaf is the part used; stems are also in tea (LactMed). No source read compared other parts.

No measurements of lead, cadmium, arsenic, aluminium or pesticides in gyokuro were found in the sources read, so that is unknown here, not shown safe. Fluoride was looked up only for green tea in general.

Fluoride. Tea leaves take up fluoride. A scoping review of 88 studies gave average levels of brick tea 4.78 mg/L, black tea 2.73, green tea 1.37, white tea 0.49 and herbal tea 0.17; longer brewing released more. A Canary Islands study found black and mixed teas could give children aged 4 to 8 a large share of the EFSA upper limit; the abstract did not give green tea. These are green tea averages, not gyokuro measurements. ^{15 23}

Heavy metals and pesticides. Not found in the sources read for green tea. Not described is not proof of none.

Supplement quality. LactMed notes that dietary supplements are not pre-approved by the FDA and labelled and actual ingredients and amounts can differ. In the case report, lab analysis of the capsules found no contaminants but a very high EGCG level. ^{19 21}

Heavy metals and pesticides in gyokuro. Not found for gyokuro in the PubMed searches run. A search found a 2026 study of black tea in Turkey, which is a different tea and is not used here.

Body	Action	Date
NCCIH (NIH) (United States)	Says no safety concerns have been reported for green tea as a beverage in adults; lists extract side effects, rare liver injury, medicine interactions and a caffeine caution in pregnancy. Notes the FDA has approved a specific green tea extract ointment as a prescription drug for genital warts (a topical drug, not a drink or supplement). source	2025-02
EFSA (European Union)	Opinion on safety of green tea catechins: infusions prepared the traditional way are in general considered safe at EU intakes; rare liver injury after infusions; supplements providing 800 mg EGCG a day or more raised liver enzymes. source	2018-04
EMA / HMPC (European Union)	Has a final EU herbal monograph and assessment report for Camellia sinensis non fermentatum folium (green tea); EMA page lists the therapeutic area as "Fatigue and weakness". source	2014-04-29 (monograph); 2022-09-26 (assessment addendum)
NICHD LactMed (United States)	Notes caffeine-related infant fussiness only at extremely high maternal intake; tea directly to infants can cause anemia; no oral extract data in breastfeeding. source	2006
NHS (United Kingdom)	Pregnancy: no more than 200 mg of caffeine a day; about 75 mg in a cup of black or green tea. source	2026-06-15
US FDA (United States)	Caffeine consumer update: green tea 37 mg per 12 fl oz; 400 mg a day not generally associated with harm in most adults; lists signs of too much caffeine. source	2024-08-28
IARC (WHO) (International)	Very hot beverages probably carcinogenic to humans (Group 2A); temperature, not the drink, appears responsible. source	2016-06-15

When to get medical help

Yellow skin or eyes, dark urine, pale stools, strong tiredness, itching or pain in the upper right belly while using green tea extract: stop it and get medical care now.
Chest pain, a racing or irregular heartbeat, fainting: call emergency services.
Black stools, unusual bruising or bleeding if you take warfarin: contact your prescriber or emergency services.
Very pale skin, breathlessness or marked tiredness in someone who drinks a lot of tea and has low iron: see a clinician.

Stop using the product 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

What is gyokuro?

Gyokuro is a Japanese green tea made from Camellia sinensis. The plants are shaded with screens or cloth for about 20 days before harvest, and the leaves are then steamed and dried. Shading gives a leaf high in theanine.

^{27 28 35}

How much caffeine and theanine does gyokuro contain?

In a 2025 Japanese lab study, dry gyokuro leaf held 35.41 mg of caffeine and 30.84 mg of theanine per gram, more of both than the sencha types tested (24.70 to 31.01 mg caffeine and 17.65 to 20.37 mg theanine per gram). These are lab averages of blended market samples, and real products vary.

²⁷

Is gyokuro stronger in caffeine than other green teas?

Per gram of leaf, yes in that study. In the authors' own test infusions gyokuro also came out much stronger than a superior sencha, but it was made with much more leaf in less water, so the comparison is not like for like. The FDA and NHS cup figures for green tea are not measurements of gyokuro.

^{27 31 33}

Is gyokuro the same as matcha?

No. Both come from shaded plants, but gyokuro leaf is steeped and removed, while matcha is shaded leaf ground to powder. They are different products with separate pages.

^{28 27}

Does gyokuro calm you down or help focus?

It has not been tested. Theanine and caffeine given as compounds gave a moderate short-term lift in attention, and theanine supplements gave a modest, uncertain effect on stress. The stress result depended on studies at high risk of bias. A mouse study of gyokuro showed a stress marker fell, which does not show the same in people.

^{4 7 26}

Is gyokuro the same as green tea extract?

No. A cup of tea is a water extract of the leaf. Capsules and tablets are concentrated catechins and have been linked to rare serious liver injury. NCCIH reports no safety concerns for the drink in adults. Do not carry safety or benefit results from one to the other.

^{32 5 12}

Can gyokuro hurt the liver?

The drink rarely does. EFSA judged traditional green tea infusions generally safe at European intakes but noted rare liver injury after infusions, most probably an individual reaction. EFSA also found that supplements with high EGCG raised liver enzymes in trials, and LiverTox lists liver failure for extracts. Stop any extract and get medical care if you notice yellow skin or eyes or dark urine.

^{5 20 21 12 32}

Is gyokuro safe in pregnancy or breastfeeding?

It is not banned, but it carries a lot of caffeine that counts toward your daily limit. The NHS says no more than 200 mg of caffeine a day in pregnancy, and a 2014 meta-analysis linked higher intake with more miscarriage, stillbirth and low birth weight with no clear safe threshold, though the links may be partly bias. LactMed reports infant fussiness only at extremely high maternal caffeine. Ask your midwife or doctor.

^{33 8 19 27}

Does gyokuro interact with medicines?

No gyokuro-specific interaction was found. For green tea in general, NCCIH says high doses lowered blood levels of nadolol, the extract lowered atorvastatin, and a study showed an interaction with raloxifene. One 1999 case report links very large amounts of green tea with weaker warfarin effect. Caffeine can also add to other stimulants. Ask your pharmacist or prescriber.

^{32 25 31}

Does gyokuro help with cholesterol, weight or blood pressure?

Not shown for gyokuro. For green tea in general, pooled trials found small and unstable falls in cholesterol and blood pressure and almost no weight change outside Japan. A review of short tea trials found no effect on cholesterol or blood pressure. Evidence is low.

^{29 22 14 16 9}

Does gyokuro prevent cancer or help diabetes?

No. A Cochrane review of 142 studies on green tea found limited, inconsistent, low-certainty evidence on cancer, and a meta-analysis of 14 trials found no significant effect of green tea supplements on blood sugar in type 2 diabetes. Talk to your doctor before changing diabetes care.

^{6 3}

Does tea affect iron, and is very hot tea a problem?

Tea polyphenols lowered iron absorption in a lab study (green tea was not tested), and a 2024 case report links moderate green tea with severe iron-deficiency anemia. IARC classed very hot beverages as probably carcinogenic to the oesophagus; it is the temperature, not the tea.

^{13 10 30}

Explore by health goal

Heart Health Mental Clarity Better Focus Stress Relief Mood Balance Sleep Support Cholesterol Balance Blood Pressure Support Weight Management Longevity Preventive Wellness Brain Health Healthy Aging Blood Sugar Balance Metabolic Health

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 and read the abstracts of about 28 sources, read the open-access full text of the 2025 Japanese green tea composition paper for its leaf and infusion tables, read the NCCIH, FDA, NHS and EMA pages and the IARC press release for the green tea page the same day, re-read the EFSA abstract, checked the plant name in GBIF and three compounds in PubChem, and looked for LiverTox and LactMed (summary records read; the full LiverTox page was not opened). Only abstracts were read for most papers. Certainty ratings are the compiler's own reading. One theanine trial was funded by the supplement maker. No study is cited that we could not verify.
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. This page is information, not a recommendation to drink or take anything.

Sources 38

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

Abe SK, Saito E, Sawada N, et al. Green tea consumption and mortality in Japanese men and women: a pooled analysis of eight population-based cohort studies in Japan. European Journal of Epidemiology. 2019. PMID 31392470. DOI 10.1007/s10654-019-00545-y. (abstract)
Acosta L, Byham-Gray L, Kurzer M, et al. Hepatotoxicity with High-Dose Green Tea Extract: Effect of Catechol-O-Methyltransferase and Uridine 5-Diphospho-glucuronosyltransferase 1A4 Genotypes. Journal of Dietary Supplements. 2023. PMID 36178169. DOI 10.1080/19390211.2022.2128501. (abstract)
Asbaghi O, Fouladvand F, Gonzalez MJ, et al. Effect of green tea on glycemic control in patients with type 2 diabetes mellitus: A systematic review and meta-analysis. Diabetes & Metabolic Syndrome. 2021. PMID 33285391. DOI 10.1016/j.dsx.2020.11.004. (abstract)
Camfield DA, Stough C, Farrimond J, Scholey AB. Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis. Nutrition Reviews. 2014. PMID 24946991. DOI 10.1111/nure.12120. (abstract)
EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS), Younes M, Aggett P, et al. Scientific opinion on the safety of green tea catechins. EFSA Journal. 2018. PMID 32625874. DOI 10.2903/j.efsa.2018.5239. (abstract)
Filippini T, Malavolti M, Borrelli F, et al. Green tea (Camellia sinensis) for the prevention of cancer. Cochrane Database of Systematic Reviews. 2020. PMID 32118296. DOI 10.1002/14651858.CD005004.pub3. (abstract)
Gerolymos C, Saddier E, Boyer L, Fond G. Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials. Molecular Psychiatry. 2026. PMID 42410082. DOI 10.1038/s41380-026-03727-9. (abstract)
Greenwood DC, Thatcher NJ, Ye J, et al. Caffeine intake during pregnancy and adverse birth outcomes: a systematic review and dose-response meta-analysis. European Journal of Epidemiology. 2014. PMID 25179792. DOI 10.1007/s10654-014-9944-x. (abstract)
Hartley L, Flowers N, Holmes J, et al. Green and black tea for the primary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews. 2013. PMID 23780706. DOI 10.1002/14651858.CD009934.pub2. (abstract)
He Y, Chen J. Severe iron-deficiency anemia after short-term moderate consumption of green tea in woman: A rare case report. Heliyon. 2024. PMID 39263133. DOI 10.1016/j.heliyon.2024.e36666. (abstract)
Hidese S, Ogawa S, Ota M, et al. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Nutrients. 2019. PMID 31623400. DOI 10.3390/nu11102362. (abstract)
Hu J, Webster D, Cao J, et al. The safety of green tea and green tea extract consumption in adults - Results of a systematic review. Regulatory Toxicology and Pharmacology. 2018. PMID 29580974. DOI 10.1016/j.yrtph.2018.03.019. (abstract)
Hurrell RF, Reddy M, Cook JD. Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages. British Journal of Nutrition. 1999. PMID 10999016. (abstract)
Igho-Osagie E, Cara K, Wang D, et al. Short-Term Tea Consumption Is Not Associated with a Reduction in Blood Lipids or Pressure: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Journal of Nutrition. 2020. PMID 33188386. DOI 10.1093/jn/nxaa295. (abstract)
Jayasingha H, Amarasooriya G, Rajapaksha N, et al. Fluoride in tea: accumulation, dietary exposure, and future strategies for risk mitigation in food safety; a scoping review. Critical Reviews in Food Science and Nutrition. 2025. PMID 40504749. DOI 10.1080/10408398.2025.2516756. (abstract)
Jurgens TM, Whelan AM, Killian L, et al. Green tea for weight loss and weight maintenance in overweight or obese adults. Cochrane Database of Systematic Reviews. 2012. PMID 23235664. DOI 10.1002/14651858.CD008650.pub2. (abstract)
Kakutani S, Watanabe H, Murayama N. Green Tea Intake and Risks for Dementia, Alzheimer's Disease, Mild Cognitive Impairment, and Cognitive Impairment: A Systematic Review. Nutrients. 2019. PMID 31137655. DOI 10.3390/nu11051165. (abstract)
Mancini E, Beglinger C, Drewe J, et al. Green tea effects on cognition, mood and human brain function: A systematic review. Phytomedicine. 2017. PMID 28899506. DOI 10.1016/j.phymed.2017.07.008. (abstract)
NICHD / NLM. Drugs and Lactation Database (LactMed): Green Tea. LactMed (NCBI Bookshelf). 2006. PMID 30000907. (abstract)
NIDDK. LiverTox: Green Tea (Clinical and Research Information on Drug-Induced Liver Injury). LiverTox (NCBI Bookshelf). 2012. PMID 31643260. (abstract)
Pillukat MH, Bester C, Hensel A, et al. Concentrated green tea extract induces severe acute hepatitis in a 63-year-old woman - a case report with pharmaceutical analysis. Journal of Ethnopharmacology. 2014. PMID 24862489. DOI 10.1016/j.jep.2014.05.015. (abstract)
Rezaei M, Akhavan N, Fathi F, et al. Effect of green tea supplementation on blood pressure in adults: a GRADE-assessed systematic review and dose-response meta-analysis of randomised controlled trials. Blood Pressure. 2025. PMID 40497293. DOI 10.1080/08037051.2025.2517122. (abstract)
Rodriguez I, Burgos A, Rubio C, et al. Human exposure to fluoride from tea (Camellia sinensis) in a volcanic region - Canary Islands, Spain. Environmental Science and Pollution Research. 2020. PMID 32740848. DOI 10.1007/s11356-020-10319-9. (abstract)
Saklar S, Ertas E, Ozdemir IS, et al. Effects of different brewing conditions on catechin content and sensory acceptance in Turkish green tea infusions. Journal of Food Science and Technology. 2015. PMID 26396411. DOI 10.1007/s13197-015-1746-y. (abstract)
Taylor JR, Wilt VM. Probable antagonism of warfarin by green tea. Annals of Pharmacotherapy. 1999. PMID 10332534. DOI 10.1345/aph.18238. (abstract)
Unno K, Hara A, Nakagawa A, et al. Anti-stress effects of drinking green tea with lowered caffeine and enriched theanine, epigallocatechin and arginine on psychosocial stress induced adrenal hypertrophy in mice. Phytomedicine. 2016. PMID 27765356. DOI 10.1016/j.phymed.2016.07.006. (abstract)
Unno K, Ikka T, Yamashita H, et al. Stress-Relieving Effects of Japanese Green Tea: Evaluation Using the Molar Ratio of Caffeine and Epigallocatechin Gallate to Theanine and Arginine as an Indicator. Foods. 2025. PMID 39796392. DOI 10.3390/foods14010103. (abstract)
Unno K, Kameoka Y, Nakamura Y. Compositional Diversity and Functional Interactions of Bioactive Compounds in Japanese Green Tea: Focus on Matcha, Sencha, and Gyokuro. Molecules. 2026. PMID 42654013. DOI 10.3390/molecules31162934. (abstract)
Zheng XX, Xu YL, Li SH, et al. Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials. American Journal of Clinical Nutrition. 2011. PMID 21715508. DOI 10.3945/ajcn.110.010926. (abstract)
n/a. IARC (WHO): Press release no. 244, coffee, mate and very hot beverages (15 June 2016). n/a. 2016. (full-text)
n/a. FDA: Spilling the Beans: How Much Caffeine Is Too Much? (content current as of 28 Aug 2024). n/a. 2024. (full-text)
n/a. NCCIH (NIH): Green Tea: Usefulness and Safety (last updated February 2025). n/a. 2025. (full-text)
n/a. NHS (UK): Foods to avoid in pregnancy (page last reviewed 15 June 2026). n/a. 2026. (full-text)
n/a. EMA: Camelliae sinensis non fermentatum folium (green tea), herbal medicinal product page. n/a. 2026. (abstract)
n/a. GBIF Backbone Taxonomy: Camellia sinensis (L.) Kuntze (usage key 3189635), retrieved 2026-10-25. n/a. 2026. (full-text)
n/a. PubChem: epigallocatechin gallate (CID 65064), formula C22H18O11. n/a. 2026. (full-text)
n/a. PubChem: caffeine (CID 2519), formula C8H10N4O2. n/a. 2026. (full-text)
n/a. PubChem: L-theanine (CID 439378), formula C7H14N2O3. n/a. 2026. (full-text)

Where to buy

Check the label first. Whatever you buy, look for these:

The herb is the first or only ingredient
Organic or lab-tested if that matters to you
Loose leaf or tea bags, and how long they have been stored
If you take medicines or are pregnant, ask a pharmacist about the herb first

Talk to a pharmacist or doctor before you start any supplement, especially if you take medicines. See the Safety tab for interactions.

Browse Gyokuro on Amazon

Amazon · Several brands to compare

Shop Gyokuro tea on Amazon

Support our free guides: as an Amazon Associate we earn from qualifying purchases. Full disclosure.

Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.