Background: Herbs from Lycopodium are generally reputed to be nontoxic and are occasionally used for preparing a salubrious tea. In Europe, the common Lycopodium clavatum can be easily confused with Lycopodium selago, the fir club moss. Case Report: We report 2 patients who drank a tea, erroneously prepared from dried herbs of Lycopodium selago, which resulted in sweating, vomiting, diarrhea, dizziness, cramps, and slurred speech. These symptoms were suggestive of a cholinergic mechanism. To elucidate the active principle, aqueous extracts of Lycopodium selago were checked for their suspected anticholinesterase activity using human erythrocytes as an enzyme source in a modified Ellman assay. The extracts did exhibit significant anticholinesterase activity. The anticholinesterase(s) were most effectively extracted with dichloromethane and isolated by high-performance liquid chromatography. The major compound with anticholinesterase activity co-chromatographed with authentic huperzine A, but had a 2-3-fold higher inhibitory potency than the racemic standard. The amount of huperzine A found in the Lycopodium selago sample used for the tea preparation was calculated to be sufficient for a relevant acetylcholinesterase inhibition. Conclusion: The signs and symptoms of lycopodium selago poisoning are consistent with the anticholinesterase activity of huperzine A and should favorably respond to atropine therapy. This report demonstrates once more that laymen should not be encouraged to gather their remedies from Mother Nature without advanced botanical knowledge.