Supplement analysis backed by scientific evidence · PT

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Limited evidenceBrain & cognition

Huperzine A

A potent acetylcholinesterase inhibitor sold as a supplement, which is a category error: it is pharmacologically a drug. Alzheimer's trials look positive but are almost entirely small, low-quality and from a single country, and there is essentially no evidence it helps healthy people.

What the science says

  • Alzheimer's disease Limited evidence

    A 2013 systematic review and meta-analysis of randomized trials found huperzine A improved MMSE and activities-of-daily-living scores versus placebo in Alzheimer's disease. The authors explicitly rated the methodological quality of the included trials as poor, with almost all conducted in China and inadequate reporting of randomization and blinding, so the pooled effect is unreliable.

  • Mild cognitive impairment Limited evidence

    A Cochrane review of huperzine A for mild cognitive impairment identified only one eligible trial and concluded there was insufficient evidence to determine any effect. No adequately powered MCI trial has been published since.

  • Cognitive enhancement in healthy adults Limited evidence

    There are no good placebo-controlled trials of huperzine A in cognitively normal adults, and it appears in nootropic stacks largely on mechanistic reasoning. Inhibiting acetylcholinesterase in a healthy brain is not obviously beneficial and carries real cholinergic side effects.

Dosage & safety

Studied doseAlzheimer's trials used 300-500 mcg/day (typically 100-200 mcg twice daily). Supplements usually supply 50-200 mcg/day, often as a 1% Huperzia serrata extract. Its long half-life means it accumulates; many users cycle it rather than dosing daily.
SafetyCholinergic side effects are dose-dependent and real: nausea, vomiting, diarrhoea, sweating, hypersalivation, muscle cramps and twitching, vivid dreams, insomnia and bradycardia. Contraindicated or risky with cholinesterase inhibitors (donepezil, rivastigmine), anticholinergics, beta-blockers and in asthma, COPD, bradyarrhythmias, epilepsy and peptic ulcer disease; it can also prolong the action of succinylcholine, so disclose it before surgery. Label accuracy is poor at microgram dosing, and analytical surveys of "cognitive enhancement" supplements have found substantial deviations from declared amounts. Avoid in pregnancy and breastfeeding.

Scientific references

Where to buy

California Gold Nutrition, Huperzine A, 250 mcg , 90 Veggie Capsules

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