If promising, study results will be used to design larger, definitive clinical trials to determine the efficacy of aripiprazole in reducing methamphetamine use and corresponding methamphetamine-associated sexual risk among MSM. This pilot study is therefore designed to reflect the structure of such trials. We will enroll 90 sexually active, methamphetamine-dependent individuals who will be randomized 1:1 to receive aripiprazole (n=45) or placebo (n=45) for 12 weeks. Because we are testing a drug for a new indication in a new population, we will include extensive safety parameters, as done in prior studies of pharmacologic interventions among substance users. We will also include both urine testing and extensive behavioral risk assessments because we anticipate that future definitive efficacy trials will analyze both substance use and sexual risk behavior outcomes. Study participants will be seen at the San Francisco Department of Public Health AIDS Office where they will provide urines for drug testing and participate in substance use counseling. All participants will receive HIV risk-reduction counseling. Behavior will be assessed using standardized measures via audio computer-assisted self-interview (ACASI).