Abuse of amphetamine-type substances including MDMA (ecstasy) and novel cathinone designer drugs is prevalent in our society. The studies proposed here will provide first data on the role of the DA transporter in the human pharmacology and toxicology of MDMA, on the social cognitive effects of MDMA and methylphenidate (Ritalin) in humans, and on the pharmacology of novel cathinone designer amphetamines in vitro. This work will increase our understanding of the pharmacology of amphetamine-type stimulants and help in the treatment of stimulant addiction and stimulant intoxication.