The investigators recently conducted a double-blind, randomized controlled trial (n=60) of limited duration (12 weeks), and found that compared with placebo, oral mirtazapine, an FDA-approved antidepressant, significantly reduced meth use in those receiving mirtazapine, as determined by reduction in meth-positive urines. Sexual risk behaviors also declined significantly in the mirtazapine arm compared to placebo. Mirtazapine decreased meth use despite low adherence: by medical event monitoring system (MEMS) caps, only 48.5% of daily doses were taken. All participants received weekly substance use counseling and monthly, brief clinician-delivered adherence counseling. The investigators propose expanding upon these results by lengthening the treatment period to 24 weeks, with adherence reminders added to the counseling, and determining if efficacy is sustained up to 12 weeks after drug discontinuation. The sample size for this 9-month study is 120.