Benefits
Prescription use under medical supervision
Huperzine A is approved in China as a drug for Alzheimer's disease and is sold in the US as a dietary supplement. A meta-analysis of 20 randomized trials in Alzheimer's patients, 19 run in China, found better cognition and daily function scores than comparison groups, but most trials were at high risk of bias and funnel plots suggested publication bias, so the authors urged caution. This is drug evidence in diagnosed patients.
Cognitive scores in a 16-week US randomized trial
In 210 people with mild to moderate Alzheimer's disease, 200 mcg twice daily did not improve the main cognitive score versus placebo. A 400 mcg twice-daily arm improved it at week 11 (p = 0.001), but the week 16 difference was not significant (p = 0.07). The trial was co-funded by the US National Institute on Aging and the company Neuro-Hitech, Inc.
Memory outside prescription use
A Cochrane review found no eligible placebo-controlled trials in mild cognitive impairment. One matched-pair study in 68 Chinese middle-school students who reported memory problems found higher memory scores after 4 weeks of 100 mcg twice daily than on placebo; it was small, gave no side-effect data, and enrolled adolescents, not adults.
Memory scores in a second US randomized trial
In a small US pilot trial in adults recovering from moderate to severe traumatic brain injury, 12 weeks of huperzine A did not improve memory more than placebo. Both groups improved, which the authors attributed to a placebo effect. The trial stopped early after enrolling 14 of a planned 30 people.
Enzyme activity in healthy older volunteers
In a small placebo-controlled study in healthy older adults, doses rising from 100 to 400 mcg twice daily over four weeks lowered red blood cell acetylcholinesterase activity by 30 to 40% at the lowest dose and by more than 50% at 400 mcg, and were reported as well tolerated. This measures drug activity, not a health benefit.
Mechanism of action
Reversible acetylcholinesterase inhibition
Huperzine A is a potent, selective and reversible inhibitor of acetylcholinesterase, the enzyme that breaks down acetylcholine, and it crosses the blood-brain barrier easily. Chinese clinical studies reported minimal peripheral cholinergic side effects, and trials list nausea, sweating and slow heart rate among them.
Other actions seen in laboratory studies
In cell and animal studies, huperzine A blocked NMDA glutamate receptors and potassium currents, reduced oxidative stress, and protected cells from beta-amyloid and glutamate toxicity. These effects have not been shown in people.
Absorption and half-life
In 12 healthy young adults given a single 0.4 mg tablet, blood levels peaked at about 1 hour and the elimination half-life was about 12 hours (716 minutes). A crossover study in healthy Chinese men found half-lives of about 12 hours for three oral forms, with no adverse events reported.
Clinical trials
Multicenter randomized, double-blind, placebo-controlled phase II trial run by the Alzheimer's Disease Cooperative Study; placebo, 200 mcg twice daily or 400 mcg twice daily for at least 16 weeks; primary outcome ADAS-Cog change at 16 weeks for the 200 mcg dose; supported by NIH/NIA and Neuro-Hitech, Inc. (Rafii et al. 2011, Neurology)
210 people with mild to moderate Alzheimer's disease; 177 completed treatment.
The 200 mcg twice-daily dose did not change ADAS-Cog at 16 weeks versus placebo (primary outcome negative). In secondary analyses the 400 mcg twice-daily arm improved ADAS-Cog by 2.27 points vs a 0.29-point decline on placebo at week 11 (p = 0.001), and by 1.92 points vs a 0.34-point improvement on placebo at week 16 (p = 0.07, not significant). Clinician global change, behavior and daily function scales did not differ at either dose. Serious adverse events: 8.2% placebo, 13.0% and 16.2% on huperzine A (not significant); none was considered possibly related to the study drug.
Systematic review and meta-analysis of randomized trials of huperzine A versus placebo or other treatments; daily doses 0.2 to 0.8 mg for 8 to 36 weeks; 19 of the 20 trials were conducted in China. (Yang et al. 2013, PLoS One)
1,823 participants with Alzheimer's disease across 20 trials.
Pooled results favored huperzine A on MMSE and activities of daily living scales, but most trials were at high risk of bias, funnel plots suggested publication bias, and the authors said the findings should be interpreted with caution. Reported side effects were mild, mainly nausea, loss of appetite, dizziness and vomiting, with bradycardia in two trials; no trial reported severe adverse events judged related to huperzine A.
Cochrane systematic review and meta-analysis of randomized trials of huperzine A versus placebo, with outcomes at 6 and 12 weeks. (Li et al. 2008, Cochrane Database Syst Rev)
454 patients with Alzheimer's disease in 6 trials.
Pooled scores favored huperzine A on several cognitive and daily living scales, but the methodological quality of most trials was not high and only one study was of adequate quality and size. The reviewers concluded the evidence was inadequate to make any recommendation. Adverse events were mild and did not differ significantly from control groups.
Cochrane systematic review that searched international and Chinese databases and handsearched Chinese journals for randomized, placebo-controlled trials. (Yue et al. 2012, Cochrane Database Syst Rev)
Adults with mild cognitive impairment (no eligible trials were found).
No eligible trials were identified, so no meta-analysis was possible. The authors concluded that the available evidence is insufficient to judge whether huperzine A helps people with mild cognitive impairment and called for randomized, double-blind, placebo-controlled trials.
Double-blind, placebo-controlled matched-pair study; pairs matched on a psychological health inventory, memory quotient, sex and class; huperzine A 100 mcg (two 50 mcg capsules) twice daily or starch and lactose placebo for 4 weeks. (Sun et al. 1999, Zhongguo Yao Li Xue Bao)
34 matched pairs (68) of Chinese junior middle school students who reported memory problems.
Final memory quotient was 115 ± 6 on huperzine A vs 104 ± 9 on placebo (P < 0.01), and Chinese language scores rose in the huperzine A group (no figures given). The abstract reports no side-effect data and does not describe how pairs were assigned. A single small study in adolescents.
Randomized, double-blind, placebo-controlled phase II pilot of 12 weeks of treatment with follow-up to 52 weeks; the matching ClinicalTrials.gov record (NCT01676311, same principal investigator) lists titration from 100 to 600 mcg/day and early termination for slow enrollment. (Zafonte et al. 2020, Brain Inj)
Adults recovering from moderate to severe traumatic brain injury; 14 enrolled of a planned 30 per the registry.
Memory (CVLT-II) at 12 weeks did not differ between huperzine A and placebo; the placebo group improved significantly on learning and memory, and both groups improved on depression scores, which the authors attributed to a placebo effect. The registry lists seizures as serious events in 2 of 7 on huperzine A and 1 of 6 on placebo.
Placebo-controlled phase Ib study with twice-daily doses of 100, 200, 300 and 400 mcg, each for one week, measuring red blood cell acetylcholinesterase inhibition and protection against the nerve agent soman in blood samples. (Haigh et al. 2008, Chem Biol Interact)
12 healthy older volunteers, with 3 receiving placebo.
Red blood cell acetylcholinesterase was inhibited by 30 to 40% after 100 mcg and by more than 50% at 400 mcg, peaking 1.5 hours after the last dose and still about 10% below baseline at 48 hours; plasma butyrylcholinesterase was unaffected. Doses were described as well tolerated, with no specific adverse events listed.