3. JUSTIFICATION: Patients on methadone maintenance treatment have smoking prevalence rates of up 80-90% and consequently disproportionately high mortality compared to the general population. A majority of these patients express a desire to quit but are generally more heavily dependent on nicotine. Randomized controlled trials in non-drug using populations have shown varenicline to be more efficacious for smoking cessation than placebo and other smoking cessation medications. This placebo controlled research protocol will examine varenicline's effect on smoking cessation/reduction and potential sex and gender differences in a population of methadone maintained patients.