An alkaloid from Chinese club moss that reversibly inhibits acetylcholinesterase, the enzyme that breaks down acetylcholine. It is pharmacologically the same class of compound as prescription dementia medicines.
Huperzine A is one of the few things sold as a nootropic supplement that is unambiguously a drug in its behaviour. It inhibits acetylcholinesterase potently and selectively, which is the mechanism of donepezil and rivastigmine, and in China it has been used as a licensed medicine for memory impairment. The Western evidence is weaker than that history suggests: Chinese trials in Alzheimer's disease reported cognitive improvements but reviews judged their methodological quality poor, and a US randomised phase II trial found no significant benefit at the primary dose. Meanwhile the pharmacology carries real consequences, and a compound with a defined enzyme target and a dose measured in micrograms is not something to combine casually with other supplements or medicines.
Sold as
Capsule, Tablet, Nootropic blends, Standardised club moss extract
Standardised to
Micrograms of huperzine A; blends often list the extract weight rather than the alkaloid content, which obscures the actual dose — a product without this marker may not resemble what was studied.
Also known as
Selagine, Club moss extract, Qian Ceng Ta
Regulation: Sold as a dietary supplement in the US with no pre-market efficacy review, despite being an acetylcholinesterase inhibitor. It has been used as a licensed medicine in China and is regulated as a drug in some jurisdictions. Its presence in multi-ingredient nootropic blends means people frequently take it without realising they are taking a cholinergic drug.
What the research used
The amounts, forms and durations published trials of Huperzine A actually administered.
These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.
Studied for Alzheimer's disease trials
200–800 µg
Limited
Divided doses, usually twice daily · 8–24 weeks
The dose range across Chinese trials and a US phase II study. The US trial found no significant benefit at 400 µg twice daily on its primary outcome, and Cochrane reviewers described the Chinese trial quality as poor.
Studied for Nootropic supplement use
50–200 µg
Not enough
Capsule, daily
What supplement products contain. There is no trial supporting use in healthy people, and cholinergic side effects are dose-related.
This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.
When it was taken
Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.
None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.
🌅Morning
Not enough
Usually dosed in the morning or divided, following the trial protocols. Some users cycle it on the assumption of receptor downregulation, which has not been tested.
Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.
The evidence in depth
Best supported: Not enough
What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.
Chinese trials in Alzheimer's disease reported cognitive improvements, but systematic reviewers judged the studies of poor methodological quality, and a better-controlled US trial found no significant effect. There is no evidence at all for cognitive enhancement in healthy people.
What may be going on: Huperzine A reversibly inhibits acetylcholinesterase, raising synaptic acetylcholine. It also has NMDA receptor activity in laboratory work.
Not enough evidence. Not enough human research to say anything useful yet.
Deep research mode adds each paper’s own conclusion and stated limitations.
Things to know
Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.
Worth knowing
It is a real acetylcholinesterase inhibitor
This is the same pharmacological class as prescription dementia drugs, sold without prescription and frequently hidden inside blends. Cholinergic effects — nausea, vomiting, sweating, salivation, diarrhoea, muscle twitching, slowed heart rate, vivid dreams and insomnia — are dose-related and can be significant. It should not be regarded as a herbal extract with mild effects.
Interaction
Additive with cholinergic drugs, opposed by anticholinergics
Combining it with donepezil, rivastigmine, galantamine or other cholinesterase inhibitors risks cholinergic excess. It opposes anticholinergic medicines, and it interacts with drugs that slow heart rate including beta-blockers. It can also prolong the effect of certain anaesthetic muscle relaxants, which matters before surgery.
Avoid
Avoid with bradycardia, asthma, epilepsy or ulcers
Cholinergic activity can slow the heart, provoke bronchoconstriction, increase gastric acid and lower seizure threshold. Anyone with a slow heart rate, asthma, chronic obstructive lung disease, epilepsy or peptic ulcer disease should avoid it, as should anyone pregnant or breastfeeding.
Worth knowing
Hidden in nootropic blends
Huperzine A appears in many multi-ingredient focus and memory products, sometimes only as a club moss extract weight rather than a stated microgram dose. People stacking several such products can take considerably more than they realise.