to psilocybin. Psilocybin is rapidly dephosphorylated in the body to psilocin, which is a partial agonist for several serotonergic receptors . Psilocin has a high affinity for the 5-HT 2A serotonin receptor in the brain, where it mimics the effects of serotonin (5-hydroxytryptamine, or 5-HT). Psilocin binds less tightly to other