Huperzine A is a naturally occurring sesquiterpene alkaloid compound found in the firmoss Huperzia serrata and in varying quantities in other Huperzia species, including H. elmeri, H. carinat, and H. aqualupian. Huperzine A has been investigated as a treatment for neurological conditions such as Alzheimer's disease, but a meta-analysis of those studies concluded that they were of poor methodological quality and the findings should be interpreted with caution.
Huperzine A is extracted from Huperzia serrata. It is a reversible acetylcholinesterase inhibitor and NMDA receptor antagonist that crosses the blood-brain barrier. The structure of the complex of huperzine A with acetylcholinesterase has been determined by X-ray crystallography.
For some years, huperzine A has been investigated as a possible treatment for diseases characterized by neurodegeneration, particularly Alzheimer's disease. A 2013 meta-analysis found that huperzine A may be efficacious in improving cognitive function, global clinical status, and activities of daily living for individuals with Alzheimer’s disease. However, due to the poor size and quality of the clinical trials reviewed, huperzine A should not be recommended as a treatment for Alzheimer’s disease unless further high quality studies confirm its beneficial effects.
Huperzine A is also marketed as a dietary supplement with claims made for its ability to improve memory and mental function. Huperzine A has also been postulated as a potential treatment for myasthenia gravis.