Little Club Moss, also known as Huperzia serrata or simply "club moss," has a long history of use in traditional Chinese medicine, primarily for issues related to aging, memory, and inflammation. Its most notable constituent is huperzine A, an alkaloid that functions as an acetylcholinesterase inhibitor—meaning it slows the breakdown of acetylcholine, a neurotransmitter important for memory and learning. The acetylcholine system is integral to cognitive function, and reduced levels of acetylcholine are characteristic of conditions like Alzheimer's disease.

The traditional use of Little Club Moss for cognitive support predates modern pharmacological understanding, but contemporary research has focused specifically on huperzine A extracted from the plant. Multiple small-scale clinical studies and animal models have shown that huperzine A can increase acetylcholine levels in the brain and may improve memory and cognitive function, especially in the context of neurodegenerative diseases. However, most of the evidence comes from studies conducted in China, and there are concerns about study quality, sample size, and long-term safety.

In summary, traditional use of Little Club Moss for cognitive health laid the foundation for its modern application in supporting the acetylcholine system, but while promising, the scientific evidence is not yet robust enough for unequivocal endorsement. The evidence rating is moderate (3/5), based largely on tradition and preliminary scientific support.