The second experiment will last 10 weeks and will enroll 12 individuals addicted to cocaine. Participants will take part in various phases, which will each last several days. The phases will include a cocaine sampling phase; a cocaine acquisition phase in which participants will receive monetary rewards for distinguishing between cocaine and placebo; a placebo phase; an aripiprazole maintenance phase; a cocaine dose response phase in which the ability of aripiprazole to reduce cocaine's stimulating effects will be examined; and a washout phase in which no drugs will be given. Cocaine and aripiprazole doses will be determined by the results of the first experiment.