Methamphetamine use is especially prevalent among men who have sex with men (MSM). Population-based surveys report methamphetamine use rates 20 times higher among MSM compared with the general population. Methamphetamine use is also a driving force in the MSM HIV epidemic: methamphetamine use has been associated with increased number of sexual partners, unprotected sex acts, and sexually transmitted infection (STI) and HIV acquisition. Despite these alarming data, relatively few interventions have been tested among methamphetamine-using MSM, and no studies have tested the efficacy of pharmacologic interventions in reducing methamphetamine use in this population. In parallel with the continued testing of behavioral approaches, we believe the time has come to test pharmacologic interventions to reduce methamphetamine use among MSM. Pharmacologic approaches to treating substance use have been successful in treating nicotine, alcohol, and heroin dependence. No studies have tested a pharmacologic intervention to reduce methamphetamine use among MSM at high risk for HIV acquisition and transmission. A recent pilot study found that mirtazapine, a drug with dual dopaminergic and serotonergic properties, significantly reduced methamphetamine withdrawal symptoms when compared to placebo over a two-week period among Thai men in a drug probation center. Mirtazapine is a commonly used, FDA-approved antidepressant; however, in the Thai study its effects on methamphetamine withdrawal were independent of its effects on depressive symptoms, suggesting a direct effect of mirtazapine on treating methamphetamine dependence. We propose to expand upon these promising pilot results by conducting a study of intermediate size (60 participants) and length (3 months of follow-up) to assess the efficacy of mirtazapine in reducing methamphetamine use among high-risk MSM.