Holy basil (tulsi): what the evidence shows for stress and blood sugar

Tulsi is grown in homes and temples across India and is central to Ayurvedic and Siddha practice. It is brewed as a tea, taken as a tincture or powder, or sold in capsules as an "adaptogen" for stress. Several UK tea brands now carry it, usually with food-style descriptions rather than medicinal ones.

The plant should not be confused with the sweet basil of the kitchen, or with other Ocimum species. Different species and chemotypes have different essential oil compositions, which is one reason evidence for one cannot simply be applied to another.

A systematic review published in 2017 in Evidence-Based Complementary and Alternative Medicine searched books, theses, conference proceedings and databases including Cochrane, Embase and Medline for human studies that reported a clinical outcome after ingesting tulsi. It identified 24 studies. They reported therapeutic effects in metabolic disorders, cardiovascular disease, immunity and neurocognition, and all of them reported favourable outcomes, with no study reporting any significant adverse event. The authors suggested the studies reinforce traditional uses and that tulsi may be an effective treatment for lifestyle-related chronic diseases including diabetes, metabolic syndrome and psychological stress.

The same authors added that further studies are required to explore mechanisms, clarify dosage and dose form, and determine which populations are most likely to benefit. This is important, because a body of evidence in which every study is positive is more likely to reflect small samples, variable methods and selective publication than a uniformly powerful remedy. The review does not say tulsi treats diabetes or anxiety disorder; it says the preliminary human data support further research.

• Small and varied studies, with different preparations, doses and durations.

• Many outcomes are intermediate measures such as fasting glucose, rather than long-term outcomes.

• No head-to-head comparison with established treatments is described in the abstract.

• The review included studies published outside mainstream journals, whose quality can vary.

For diabetes, the practical risk lies in combining a plant that may lower glucose with prescribed medicine. Someone on insulin, gliclazide or similar drugs who begins regular tulsi capsules should tell their diabetes team and recognise hypoglycaemia symptoms. For stress and low mood, a herb is no substitute for assessment when symptoms last more than a couple of weeks, interfere with work or sleep, or involve thoughts of self-harm. Those need a GP, NHS Talking Therapies self-referral or NHS 111, and in an emergency, 999.

Tulsi tea in ordinary cup quantities carries little concern reported in the sources used here. Concentrated extracts are less well characterised, and the NHS general advice applies: avoid herbal medicines in pregnancy, breastfeeding and kidney or liver problems unless a clinician says otherwise, and do not give them to children without advice. The NHS also lists blood thinners, diabetes drugs, antidepressants, statins, blood pressure medicines and hormonal contraception among medicines that herbal products can interact with.

Tulsi products vary widely. Labels may say "holy basil", "tulsi" or a Latin name, and some capsules combine it with other herbs, so check which plant is actually in the product. The MHRA identifies poor and variable quality of unregulated herbal products as a key concern, and the NHS advises against buying unlicensed herbal medicines online. Look for a Latin name, the plant part used, a batch number and a UK contact.

Sold as a food supplement or tea, tulsi should not carry claims to treat disease. If a product is presented as treating diabetes or anxiety, the MHRA may regard it as a medicine, since herbal ingredients do not exclude medicinal status and it examines claims, ingredients and presentation. A traditional herbal registration shows the MHRA assessed safety, quality and traditional use, not proven efficacy.

Tulsi tea is a pleasant, low-concern drink for most people and fits within a routine of regular meals, daylight, exercise and sleep that does much more for stress and glucose than any herb. Capsules deserve more thought: choose a named product, tell your pharmacist, watch blood sugar if you have diabetes, and stop if you notice rash, palpitations, dizziness or any new symptom. Report suspected reactions through the Yellow Card scheme.