Supplement analysis backed by scientific evidence · PT

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Limited evidenceStress & mood

Holy Basil (Tulsi)

Small trials consistently report benefits for stress and blood glucose, but that consistency is itself a red flag: literally every published human study is favourable, most are small, short and industry-linked, and none are large or independently replicated.

What the science says

  • General stress symptoms Limited evidence

    A 6-week double-blind RCT randomized 150 adults to 1200 mg/day of a standardized Ocimum tenuiflorum extract or placebo. Total self-rated stress symptom scores improved roughly 39% more than placebo, with specific gains in exhaustion, forgetfulness and recent-onset sleep problems. It is a single manufacturer-linked trial using self-rated outcomes.

  • Blood glucose and metabolic markers Limited evidence

    A systematic review of 24 human studies found reported reductions in fasting and post-prandial glucose and improvements in lipid profiles in people with type 2 diabetes or metabolic syndrome. The trials were small, short and often poorly reported, so effect sizes should not be taken at face value.

  • The uniformly positive literature is itself a warning sign Limited evidence

    The same review noted that all 24 identified human studies reported favourable clinical outcomes and none reported significant adverse events. A literature with zero negative trials is more consistent with publication bias and weak methods than with a uniformly effective herb.

Dosage & safety

Studied doseHuman trials used 300-2000 mg/day of leaf extract; the main stress trial used 1200 mg/day of standardized extract for 6 weeks, and glycaemic studies commonly used 1-2.5 g/day of leaf powder for 4-12 weeks. Preparations vary widely (aqueous extract, ethanolic extract, whole leaf powder) and are not interchangeable.
SafetyNo serious adverse events have been reported in trials, though follow-up rarely exceeds 12 weeks. Holy basil has hypoglycaemic and antiplatelet activity, so watch for additive effects with antidiabetic drugs and anticoagulants and stop before surgery. Animal studies report reversible anti-spermatogenic and anti-fertility effects at high doses in male rodents; relevance to humans is unknown but worth knowing if you are trying to conceive. Avoid in pregnancy, given traditional use as an emmenagogue and animal data suggesting anti-implantation effects. Not regulated as a medicine in most markets, so potency varies.

Scientific references

Where to buy

Frontier Co-op, Organic Holy Basil (Tulsi) Herb, 8 oz (226 g)

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