As defined in this chapter, the term psychedelic drugs includes both classic hallucinogens [i.e., indolalkylamines and phenylalkylamines, such as lysergic acid diethylamide (LSD) and mescaline, respectively], ‘‘dissociative’’ drugs [i.e., arylcyclohexamines, such as phencyclidine (PCP) and ketamine], and substituted amphetamine analogues [i.e., phenylpropanolamines, such as 3,4-methylenedioxymethamphetamine (MDMA, ‘‘ecstasy’’)].