Holy Basil for Stress, Blood Sugar and Thyroid: Evidence and Cautions
What human studies of holy basil (tulsi) found for stress, blood sugar and thyroid, how strong that evidence is, and the cautions that apply, including diabetes medicines.
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Safety first. Supplements can cause side effects and interact with medicines. Read mushroom safety and interactions before you use any mushroom product.
Short answer. Small human studies of holy basil (tulsi) report changes in blood sugar, mood and thinking tests. A 2017 systematic review judged most of them to be of limited quality, mostly from India and no longer than 13 weeks. [1] For the thyroid, we found no human evidence, only a mouse study. Holy basil is not a replacement for diabetes, thyroid or mental health care.
Before you start. This is information, not medical advice. If you take diabetes medicines, ask a pharmacist or the prescriber before adding holy basil, because trials measured lower blood sugar. Never stop or change a prescribed medicine yourself. If anxiety or low mood is affecting daily life, a clinician can help; in the US you can call or text 988 (Suicide & Crisis Lifeline) at any time.
Which plant this is
Holy basil, or tulsi, is Ocimum tenuiflorum L., family Lamiaceae. [2] Many studies use the older name Ocimum sanctum L., which GBIF lists as a synonym. [2] It is a different species from the sweet basil used in cooking (Ocimum basilicum, an accepted name in GBIF [2]); see Basil. Most trials used the leaf. [1] The full profile is at Holy basil (tulsi).Traditional use (not proof)
Tulsi is indigenous to the Indian continent and is highly revered for its medicinal uses in the Ayurvedic and Siddha medical systems. [1] Traditional use is described in Tulsi (holy basil) in Ayurveda. It does not show that a product works for a modern health goal.What research shows
| Use | What the source found | Strength of evidence | Form and people studied |
|---|---|---|---|
| Stress, anxiety, mood | In a review, three trials reported reduced anxiety and stress, and two reported reductions of 31.6%–39% in stress-related symptoms in people with psychosomatic problems compared with controls. [1] | Promising but limited | Varied forms; small trials, mostly in India |
| Thinking tests | A 4-week trial in 40 healthy young adults found better cognitive flexibility, short-term memory and attention, but no significant difference in stress levels. [1] | Promising but limited | 300 mg/day in that trial |
| Cortisol and anxiety scale | In a 30-day trial of 300 mg capsules of ethanolic leaf extract, salivary cortisol and an anxiety scale improved over time in the extract group only, but the group difference was significant only for one brain-wave timing measure. [3] | Insufficient evidence (cortisol is a biomarker, not an outcome) | Healthy adult volunteers |
| Blood sugar | Trials in type 2 diabetes reported improved fasting and after-meal glucose, for example after 4 weeks of 2.5 g of leaves daily. [1] | Promising but limited | Short trials; small groups |
| Thyroid | Proper evidence not found in people. We searched PubMed for Ocimum sanctum and thyroid hormone. | None in humans | See below |
How strong is this evidence?
- The 2017 review found 24 human studies. In its results section only three were rated high quality (Jadad scores of 4-5) and the rest scored 0 to 3. [1] Its discussion says seven of 24 can be considered high quality, so even the review counts differ. [1]
- Its authors wrote that tulsi's therapeutic effects "may have therefore been overestimated". [1]
- Almost all studies were done in India and published in local journals, and unpublished negative studies may exist. [1]
- Many studies did not give the cultivar, dosage form, dosage or quality control details. [1]
- The review said relatively few human trials exist. [1]
Blood sugar and diabetes medicines
One 12-week trial in type 2 diabetes added 300 mg of tulsi leaf extract to the drug glibenclamide and reported greater improvement in blood glucose and HbA1c than the drug alone. [1] That is encouraging for research, but it also shows tulsi can add to a medicine's effect, so a clinician should know about it. See Adaptogens for blood sugar and metabolism and prediabetes, type 2 diabetes and metabolic syndrome.Thyroid
Proper evidence not found in people. The only study we found was in male mice, where leaf extract at 0.5 g per kg for 15 days significantly lowered serum T4. [4] The authors described the extract as antithyroidic in that model. [4] Animal results do not transfer to people. If you have a thyroid condition or take thyroid medicine, ask your clinician first; see thyroid problems and fatigue.Frequently asked questions
Does holy basil lower anxiety?
Some small, mostly lower-quality trials report lower stress and anxiety. [1] A 30-day extract trial found no clear group difference on its anxiety scale. [3] Evidence is promising but limited.
Can holy basil lower blood sugar?
Trials in people with type 2 diabetes reported lower glucose. [1] If you use diabetes medicines, ask a pharmacist or prescriber first.
Does holy basil affect the thyroid?
Proper evidence not found in people. In male mice an extract lowered T4. [4]
Is holy basil the same as the basil in food?
No. Holy basil is Ocimum tenuiflorum; sweet basil used in cooking is Ocimum basilicum, a separate accepted species. [2]
Is holy basil safe long term?
Reported side effects were few in trials, but the longest lasted 13 weeks. [1] Long-term safety is not established in the sources we read.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety
- Reported side effects: in the review, 15 of 24 studies reported no adverse events, 8 did not mention them, and one reported occasional nausea. [1] But the longest study was 13 weeks, so long-term effects cannot be excluded. [1]
- Medicines: see How medicine interactions work. Diabetes medicines are the group the trials point to.
- Bleeding, surgery and fertility: not described in the sources we read. That is not proof of safety; tell the surgical team about any herb (supplements before surgery).
- Pregnancy, breastfeeding, children, older adults, liver and kidney disease: Proper evidence not found. We searched PubMed and the LactMed database for holy basil, and NIH's herb page was not available to us. Ask a clinician; see pregnancy and breastfeeding.
- Forms: studies used leaf powder, fresh leaf juice, extracts and whole-plant extract. [1] We did not find a trial of a tincture in the sources we read, so results do not transfer to one. See quality testing and certifications.
References
- Jamshidi N, Cohen MM. The Clinical Efficacy and Safety of Tulsi in Humans: A Systematic Review of the Literature. Evidence-Based Complementary and Alternative Medicine. 2017. Read 2026-10-23.
- GBIF Secretariat. GBIF Backbone Taxonomy, species records for Panax ginseng, Eleutherococcus senticosus, Ocimum tenuiflorum and Lepidium meyenii. Read 2026-10-23.
- Sampath S, et al. Holy basil (Ocimum sanctum Linn.) leaf extract enhances specific cognitive parameters in healthy adult volunteers: A placebo controlled study. Indian Journal of Physiology and Pharmacology. 2015. Read 2026-10-23.
- Panda S, Kar A. Ocimum sanctum leaf extract in the regulation of thyroid function in the male mouse. Pharmacological Research. 1998. Read 2026-10-23.