A Chinese medicine with use dating back hundreds (if not thousands) of years, healers have used the moss Huperzia serrata as part of their medical armamentarium. The moss is found in northern areas of China and has been employed as a fever and inflammation remedy. While some research backs up the historical applications of this medicinal moss, modern science has uncovered far more uses for this plant. More specifically, an alkaloid extract of the moss, known as huperzine A, has impressive effects on conditions involving the brain.
Huperzine A appears to work on areas of memory and can possibly benefit those with loss of short term memory; as well as in conditions of long term memory loss, such as Alzheimer's disease. Other information relating to its usefulness in treating fevers and inflammation (historical uses) remain to be elucidated by modern research. However, given the wisdom of thousands of years of efficient usage, huperzine A may indeed be helpful for such conditions.
The extract of the moss, huperzine A, is classified as an alkaloid chemical. Huperzine A is derived from two different types of Chinese club moss, Huperzia serrata and Lycopodium selago. 
Huperzine A directly affects the concentration of a particular neurotransmitter in the brain known as acetylcholine. [2, 3] This medicine works by stopping or slowing the enzyme (acetylcholinesterase, AChE) responsible for breaking down this neurotransmitter for a specified period of time; hence it is known as a reversible acetylcholinesterase inhibitor.
Under normal conditions in the brain, acetylcholine is released and acts upon specific neurons. Once it has performed its function, the enzyme acetylcholinesterase comes along and ‘sweeps up’ the remaining acetylcholine. Huperzine A effectively slows this action, leaving acetylcholine around for longer periods of time. Scientists believe this may be the reason why Huperzine A has positive effects on certain brain conditions.
Huperzine A is thought to act on AChE for up to 3 hours, and may be more effective than certain pharmaceutical AChE inhibitors (i.e. tacrine, Cognex or donzepril, Aricept). [4, 5] In one particular study, huperzine A was shown to be 64 times more effective than one of these medications (tacrine), and to be better distributed in the brain than this drug.  In addition to working as well as commonly prescribed drugs, huperzine A can protect brain cells in certain conditions as well. For example, glutamate is an amino acid that can become toxic to brain cells when it reaches a certain concentration; huperzine A also protects against glutamate-induced neuronal damage.  Huperzine A is protective against another type of experimental neurotoxin, N-methyl-D-aspartate, or NMDA. [6, 7] Huperzine A is protective against certain seizure-inducing nerve agents as well. 
Areas where huperzine A excels also includes improving memory function in healthy individuals. In one study, highlighting school children that complained of poor memory, huperzine supplementation was shown to improve memory after only four weeks of supplmentation. 
In treatments of dementia, huperzine A supplementation has been shown to improve the memory, behavior, and cognitive function in people with Alzheimer’s disease, brain damage caused by strokes, and in the very elderly who suffer from senile-induced dementia. [10-12] In these studies, treatment times ranged from two to eight weeks of supplementation.
Another interesting area of success with huperzine A is within the treatment of the disease myasthenia gravis (MG). MG is an autoimmune condition in which acetylcholine receptors in the muscles are attacked by the person’s own immune system. By administering huperzine A, muscle weakness was delayed in MG patients who received the medicine by intramuscular injection.  Compared to neostigmine, a commonly used drug for this condition, huperzine A had a longer duration of effect.
Taken orally, huperzine A is dosed from 50 micrograms to 200 micrograms, twice per day. Studies investigating its intramuscular use utilized 400 micrograms per day.
Huperzine Side effects:
Some reported side effects of huperzine A supplementation include blurry vision, sweating, nausea, loss of appetite, muscle twitching, and insomnia. [13, 14]
Conditions in which huperzine A may be contraindicated include pregnancy and lactation; no studies have been performed regarding its safety, however. Other conditions with potential reactions include; cardiovascular disease (huperzine can slow the heart rate), epilepsy (may worsen seizure disorders), ulcers (huperzine can enhance gastric juice secretion), asthma or chronic obstructive pulmonary disease (huperzine may increase lung secretions), and urinary tract obstructions (huperzine may increase secretions here as well).
Note: Huperzine A, although derived from a plant, is a constituent that has undergone laboratory modification. Avoid confusing prescription names of huperzine A (Cerebra, selagine) with similar-sounding prescription drugs (e.g. Celebrex, Celexa, Cerebyx and selegiline). 
General interactions (supplement, herb, food, lab):
Huperzine A does not appear to interfere with any other supplements, herbs, foods, or lab tests.
Huperzine Drug interactions:
Because of the apparent inhibitory effect of huperzine A on AChE, using it with acetylcholinesterase inhibitor drugs may lead to additive effects. This includes the drugs; tacrine (Cognex), succinylcholine (Anectine, Quelicin), echothiophate (Phospholine Iodide, bethanechol (Urecholine), donepezil (Aricept), edrophonium (Enoln, Reversol, Tensilon), neostigmine (Prostigmin), physostigmine (Antilirium), and pyridostigmine (Mestinon, Regonol).
Using huperzine A with anticholinergic drugs may decrease the effectiveness of huperzine A, as these drugs counter its effects on acetylcholine. Anticholinergic drugs include: scopolamine, atropine, biperiden (Akineton), benztropine (Cogentin), trihexyphenidyl (Artane), and procyclidine (Kemadrin).
Using huperzine A with cholinergic drugs (these promote the activity of acetylcholine in the body) may lead to additive effects. These drugs include; bethanechol (Urecholine), donepezil (Aricept), echothiophate (Phospholine Iodide), edrophonium (Enoln, Reversol, Tensilon), neostigmine (Prostigmin), physostigmine (Antilirium), pyridostigmine (Mestinon, Regonol), succinylcholine (Anectine, Quelicin), and tacrine (Cognex).
1. Pepping J. Huperzine A. Am J Health Syst Pharm 2000;57:530-4.
2. Xiong ZQ, Cheng DH, Tang XC. Effects of huperzine A on nucleus basalis magnocellularis lesion-induced spatial working memory deficit. Chung Kuo Yao Li Hsueh Pao 1998;19:128-32.
3. Cheng DH, Tang XC. Comparative studies of huperzine A, E2020, and tacrine on behavior and cholinesterase activities. Pharmacol Biochem Behav 1998;60:377-86.
4. Skolnick AA. Old Chinese herbal medicine used for fever yields possible new Alzheimer Disease therapy. JAMA 1997;277:776.
5. Wang H, Tang XC. Anticholinesterase effects of huperzine A, E2020, and tacrine in rats. Chung Kuo Yao Li Hsueh Pao 1998;19:27-30. 1 Ibid 4 Ibid
6. Wang XD, Zhang JM, Yang HH, Hu GY. Modulation of NMDA receptor by huperzine A in rat cerebral cortex. Chung Kuo Yao Li Hsueh Pao 1999;20:31-5.
7. Lallement G, Veyret J, Masqueliez C, et al. Efficacy of huperzine in preventing soman-induced seizures, neuropathological changes and lethality. Fundam Clin Pharmacol 1997;11:387-94.
8. Grunwald J, Raveh L, Doctor BP, Ashani Y. Huperzine A as a pretreatment candidate drug against nerve agent toxicity. Life Sci 1994;54:991-7.
9. Sun QQ, Xu SS, Pan JL, et al. Huperzine-A capsules enhance memory and learning performance in 34 pairs of matched adolescent students. Chung Kuo Yao Li Hsueh Pao 1999;20:601-3.
10. Xu SS, Gao ZX, Weng Z, et al. Efficacy of tablet huperzine-A on memory, cognition, and behavior in Alzheimer’s disease. Zhongguo Yao Li Xue Bao 1995;16:391-5.
11. Zhang SL. [Therapeutic effects of huperzine A on the aged with memory impairment]. [Article in Chinese]. New Drugs and Clinical Remedies 1986;5:260-2.
12. Zhang RW, Tang XC, Han YY, et al. [Drug evaluation of huperzine A in the treatment of senile memory disorders]. [Article in Chinese]. Chung Kuo Yao Li Hsueh Pao 1991;12:250-21 Ibid
13. Camps P, Cusack B, Mallender WD, et al. Huprine X is a novel high-affinity inhibitor of acetylcholinesterase that is of interest for treatment of Alzheimer’s disease. Mol Pharmacol 2000;57:409-17.
14. Cheng YS, Lu CZ, Ying ZL, et al. [128 cases of myasthenia gravis treated with huperzine A]. New Drugs and Clinical Remedies 1986;5:197-9.
15. Huperzine A, although derived from a plant, is a constituent that has undergone laboratory modification. Avoid confusing prescription names of huperzine A (Cerebra, selagine) with similar-sounding prescription drugs (Celebrex, Celexa, Cerebyx and selegiline).