An SAR study of psilocybin and psilocin derivatives reveals that 1-methylpsilocin is a selective agonist at the h5-HT2C receptor. The corresponding phosphate derivative, 1- methylpsilocybin, shows efficacy in an animal model for obsessive–compulsive disorder, as does 4-fluoro-N, N-dimethyltryptamine. These results suggest a new area for development of novel 5-HT2C agonists with applications for drug discovery.