Herbs & Supplements:
Huperzine A
Principal Proposed Uses
•
Alzheimer's Disease, Other Forms of Dementia, Ordinary Age-Related Memory Loss
Huperzine A (HUP-er-zeen) is an extremely potent chemical derived from a particular type of club moss (Huperzia serrata [Thumb] Trev.). Like caffeine and cocaine, huperzine A is a medicinally active, plant-derived chemical that belongs to the class known as alkaloids. It was first isolated in 1948 by Chinese scientists.1 This substance is really more a drug than an herb, but it is sold over the counter as a dietary supplement for memory loss and mental impairment.
What Is the Scientific Evidence for Huperzine A?
Many experiments have found that huperzine A can improve memory skills in aged animals as well as in younger animals whose memories have been deliberately impaired.2–17
All clinical trials of huperzine to date were performed in China and reported in Chinese.
A double-blind placebo-controlled study evaluated 103 people with Alzheimer's disease who received either huperzine A or placebo twice daily for 8 weeks.18 About 60% of the treated participants showed improvements in memory, thinking, and behavioral functions compared to 36% of the placebo-treated group, and the difference was significant.
Benefits were also seen in an earlier double-blind trial using injected huperzine in 160 individuals with dementia or other memory disorders.19
However, another double-blind trial of 60 individuals with Alzheimer's disease found no significant difference in symptoms between the treated and the placebo groups.20
Huperzine may also be helpful for improving memory in healthy individuals, although the evidence appears to be limited to one small, poorly designed trial.21
Huperzine A inhibits the enzyme acetylcholinesterase (uh-SEE-tul-co-lin-ES-ter-ase). This enzyme breaks down acetylcholine, which seems to play an important role in mental function. When the enzyme that breaks it down is inhibited, acetylcholine levels in the brain tend to rise. Drugs that inhibit acetylcholinesterase (such as tacrine and donepezil) seem to improve memory and mental functioning in people with Alzheimer's and other severe conditions. The research on huperzine A indicates that it works in much the same way.
The chemical action of huperzine A is very precise and specific. It "fits" into a niche on the enzyme where acetylcholine is supposed to attach.22,23 Because huperzine A is in the way, the enzyme can't grab and destroy acetylcholine. This mechanism has been demonstrated by considerable scientific work, including sophisticated computer modeling of the shape of the molecule.24
Although it originally comes from a plant, huperzine A is highly purified in a laboratory and is just a single chemical. It is just not much like an herb. Herbs contain hundreds or thousands of chemicals. In this way, huperzine A resembles drugs such as digoxin, codeine, Sudafed, and vincristine (a chemotherapy drug), which are also highly purified chemicals taken from plants. If we wish to call huperzine A a natural treatment, we need to call these (and dozens of other standard drugs) natural as well.
Dosage
Huperzine A is a highly potent compound with a recommended dose of only 100 to 200 mcg twice a day for age-related memory loss. We recommend using it only under a doctor's supervision.
Safety Issues
Perhaps because it works so specifically, huperzine A appears to have few side effects. However, children, pregnant or nursing women, or those with high blood pressure or severe liver or kidney disease should not take huperzine A except on a doctor's recommendation. We also don't know whether huperzine A interacts adversely with any drugs.
View References
Last reviewed March 2002 by Medical Review Board
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