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This is general information, not medical advice. Supplements can interact with medicines and aren’t suitable for everyone, especially in pregnancy or with a medical condition. Talk to a pharmacist or doctor before starting one.
What it is
Holy basil, or tulsi, is a fragrant plant sacred in Hindu tradition and widely grown in India. It is different from the sweet basil used in Italian cooking. Leaves are used as tea, extract or powder.
People take it for stress, low mood, blood sugar support and general resilience. It is often listed as an adaptogen and is drunk as a herbal tea in many households.
It is sold as a food supplement and herbal tea in the UK.
How it works
Its leaves contain eugenol, ursolic acid, rosmarinic acid and other compounds. These may affect stress hormones and inflammation pathways, and may influence blood sugar regulation, but human mechanisms are not well established.
What the evidence says
- Limited Stress and anxiety
Small trials report reductions in self-rated stress and anxiety, but the studies are short and low in number. - Limited Blood sugar
Small studies suggest modest reductions in fasting glucose, but this is not enough to rely on. - Weak Mood and cognition
Early work suggests small improvements, and quality is low. - Weak Immune support
Mostly lab and animal findings; little good human evidence.
Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.
Dosage and timing
- Trials commonly use 300 to 600 mg of leaf extract daily, sometimes split into two doses.
- Tea is gentler, typically one to three cups a day.
- Take with food if capsules upset your stomach.
- There is no NHS reference intake. Check current guidance and the label.
Forms and what to look for
- Standardised leaf extracts are used in research (for example with a stated ursolic acid level).
- Tea is cheap and gentle but low in dose.
- Whole leaf powder is variable.
- Check the label names Ocimum tenuiflorum or Ocimum sanctum and states the plant part.
What to expect, and when
- Tea may feel relaxing within a day or two, mostly due to the ritual.
- Extract trials usually run 4 to 8 weeks.
- If you notice nothing after two months, it is probably not for you.
Side effects
- Nausea or mild stomach upset.
- Low blood sugar in people on diabetes treatment.
- Possible effects on blood clotting.
- Occasionally headache or dizziness.
Interactions
- Diabetes medicines: risk of low blood sugar.
- Blood thinners such as warfarin: possible additive effect.
- Thyroid medication: animal data suggest effects on thyroid hormones.
- Sedatives: possible additive drowsiness.
Who should avoid it
- People who are pregnant or trying to conceive, as animal studies suggest effects on fertility.
- Breastfeeding women.
- Anyone on blood thinners or diabetes medicine without advice.
- People due for surgery within two weeks.
Risks and safety
- Animal studies suggest possible reduced fertility; human relevance is unclear.
- Herbal products may be contaminated or mislabelled.
- Not WADA-prohibited, but check batches if you compete.
Buying well: quality and testing
- Look for botanical name and part used on the label.
- Prefer standardised extracts with transparent amounts.
- Third-party tested brands are preferable.
- Avoid blends that do not list tulsi quantity.
Bottom line
Holy basil tea is a pleasant, low-risk habit. Concentrated extracts have promising but limited evidence for stress, and extra care is needed around blood sugar, blood thinners and pregnancy. It suits someone curious about a gentle herbal option, not someone seeking a proven treatment.