This supplement is made from a Chinese moss, Huperzia serrata, and has been tested in China for use in treating dementia, including Alzheimer's disease. Though the studies have generally been small and short, the findings so far have been promising. For example, in a 2012 study in Cell Biochemistry and Biophysics, huperzine A improved performance on tests of cognitive functioning and daily living in people with mild to moderate dementia, with no serious side effects, compared to a placebo. Other studies are underway. It's thought that huperzine A boosts certain brain chemicals in somewhat the same way as some prescription Alzheimer's medications, such as donepazil (Aricept) and tacrine (Cognex), though such drugs themselves have only a modest and brief effect.
Our take: Larger and longer studies are needed to confirm the current findings. But for people with dementia, huperzine A may be worth a try, under medical supervision. Keep in mind there's no evidence so far that the supplement boosts memory in healthy people or reduces the risk of dementia—which is also true, unfortunately, of all the many other supplements marketed for these purposes.
See also: Should You Be Tested for Alzheimer's?