Huperzine-A: A Cholinesterase Inhibitor in a Supplement Bottle

Huperzine-A is unusual among supplement ingredients in having a mechanism identical in kind to a class of prescription medicine. That is worth understanding before you take it daily.

The mechanism

Huperzine-A is a sesquiterpene alkaloid isolated from Chinese club moss, Huperzia serrata. It reversibly inhibits acetylcholinesterase, the enzyme that breaks down acetylcholine in the synaptic cleft. Blocking that enzyme leaves more acetylcholine available, and acetylcholine is central to memory encoding and attention. This is the same broad mechanism as donepezil and other prescription cholinesterase inhibitors used in Alzheimer's disease, which tells you the mechanism is real.

Why dose matters unusually much

Research doses are measured in micrograms rather than milligrams, and the useful range is narrow. Too little does nothing; too much produces cholinergic side effects including nausea, sweating, increased salivation, slowed heart rate, muscle twitching and vivid or disturbed dreams. A supplement that does not disclose its Huperzine-A content is asking you to take an active compound at an unknown dose, daily, indefinitely. That is a legitimate reason to ask for the supplement facts panel before buying.

Cycling and cautions

Because it is an enzyme inhibitor with a long duration of action, many practitioners suggest cycling rather than continuous daily use, though the evidence base for any particular cycling schedule is thin. Caution is warranted alongside cholinergic or anticholinergic medication and beta-blockers, and in people with bradycardia, asthma, epilepsy or gastrointestinal ulceration. It should not be combined with prescription cholinesterase inhibitors. As with any active compound, discuss it with a pharmacist if you take anything prescribed.

If you are considering Cognizil

Read the Cognizil ingredients page before ordering and check the guarantee terms. If you take any prescription medicine — including hormonal contraception — show the label to a pharmacist first, because the St. John’s Wort content genuinely matters. Our buyer’s checklist sets out twelve checks worth running.