(+/-)3,4-Methylene-dioxymethamphetamine (MDMA, or 'Ecstasy') effects on serotonin system function and behaviour in humans are unclear. Fifteen MDMA users, who did not have other drug dependencies or alcohol abuse, and had not used other drugs for prolonged periods, and 15 control individuals were included in a study to assess the biological and psychological changes after chronic use of MDMA....