Researchers in McGill University’s Department of Psychiatry are conducting a brain imaging study about the effects of stimulant drugs. We are looking for healthy volunteers (aged 18 ��" 40) who have used cocaine on multiple occasions during the past year. The study involves an interview, completion of questionnaires about personality traits and life experiences, and two brain imaging scans. All personal data will remain confidential. Participants will be compensated for their time and inconvenience. The principal investigator is Dr. Leyton.