An alkaloid with effects on the brain, notably analgesic and hallucinogenic, thought to be due to its antagonism of 5-hydroxytryptamine (5-HT). In small doses it induces psychic states, in which the individual may become aware of repressed memories. For this reason it has been used in the treatment of certain anxiety states. It is a popular drug of abuse as it induces TOLERANCE and psychological DEPENDENCE, although not physical dependence. Serious side-effects include psychotic reactions, with the risk of suicide.