This 2 x 2 factorial, randomized, double-blind, placebo-controlled trial will test two interventions: directly observed medication therapy, and long-term therapy with varenicline among smokers with opioid use disorder recruited from community-based, outpatient opioid treatment programs. The analytic strategy will evaluate the milestones in smoking cessation-achieving initial abstinence, preventing lapse and preventing relapse--necessary for long-term cessation, and evaluate theoretically-guided psychological and social factors and pharmacogenetic factors that influence these cessation processes.

Tobacco use and tobacco-related disease are highly prevalent among persons with opioid use disorders (OUD). Unfortunately, traditional evidence-based smoking cessation interventions have yielded low rates of tobacco abstinence in this group. The majority of trials evaluating smoking cessation treatment interventions among persons with OUD have relied on short-term interventions that do not account for the unique challenges faced by these smokers, specifically, establishing initial abstinence, adhering to evidence-based cessation treatments, and maintaining abstinence once active treatments cease. Long-term smoking cessation medication treatment approaches have shown promise in promoting cessation and decreasing relapse among individuals without OUD, however the applicability of extended medication approaches to smokers with OUD may be limited by poor adherence to smoking cessation medications. Though adherence to cessation medication is strongly associated with cessation success, adherence is especially challenging for persons with OUD. Opioid treatment program-based directly observed therapy (DOT) interventions improve clinical outcomes in HIV and TB, and pilot data suggest that DOT varenicline is associated with increased smoking cessation medication adherence and may increase smoking cessation rates. In this 2 x 2 factorial, randomized, double-blind, placebo-controlled trial, the investigators will test two interventions: directly observed medication therapy, and long-term therapy with varenicline. The analytic strategy will evaluate the milestones in smoking cessation-achieving initial abstinence, preventing lapse and preventing relapse--necessary for long-term cessation, and evaluate theoretically-guided psychological and social factors and pharmacogenetic factors that influence these cessation processes. The investigators will recruit smokers with OUD from community-based, outpatient opioid treatment programs and test the following specific aims: (1) to test the efficacy of directly observed varenicline therapy compared to self-administered varenicline therapy on smoking cessation milestones, (2) to test the efficacy of long-term varenicline compared to short-term varenicline on smoking cessation milestones, and (3) to understand the mechanism of smoking cessation by examining the impact of theory-guided psychological and social factors and of pharmacogenetic factors on cessation milestones.

Inclusion Criteria:

1) age ≥18 years old; 2) English or Spanish speaking (i.e., be able to participate in study interviews in English or Spanish); 3) current cigarette smoking (smoked at least 100 cigarettes/lifetime, smoking ≥ 5 cigarettes/day); 4) interest in quitting tobacco smoking; 5) receiving methadone or buprenorphine in the DoSA clinic one to six times weekly; 6) enrollment in a DoSA opioid treatment program ≥ 3 months; 7) stable methadone or buprenorphine dose for two weeks; 8) agreement to use contraception for the duration of the trial (among women with reproductive potential); 9) willingness to participate in all study components; and 10) ability to provide informed consent.

Exclusion Criteria:

1) serious or unstable disease, specifically: decompensated cirrhosis (INR≥ 1.7, albumin <2.7 g/dl or physical exam evidence of decompensated cirrhosis); severe cardiovascular disease (MI, PTCA, unstable angina, CABG, and/or serious arrhythmia in the previous 6 months); severe asthma or chronic obstructive pulmonary disease (requiring supplemental oxygen or hospitalization in past 6 months); HIV/AIDS (AIDS-defining illness or hospitalization in past 6 months); 2) creatinine clearance <30 mL/min; 3) history of seizure disorder; 4) women who are pregnant, breastfeeding, or contemplating pregnancy; 5) current suicidal ideation; 6) history of suicide attempt in the past year; 7) psychiatric hospitalization in the past year; 8) current DSM V criteria for major depressive episode, current bipolar disorder, or current psychotic disorder; 9) current DSM V criteria for alcohol use disorder; or 10) use of varenicline in the past 30 days.

Our final dataset will include: survey and laboratory data, including demographic, medical, tobacco, and other substance use-related information about all clinical trial subjects. The final dataset will be stripped of all personal identifiers.

After data collection and cleaning is complete.

We will share data with qualified investigators whose research protocols have been approved by their institutions' Institutional Review Boards. Data will be made available to potential users under a NIDA-approved data-sharing agreement that ensures that: (1) data is used only for research purposes and does not identify individual participants; (2) data is handled in a secure and confidential way; and (3) data is destroyed or returned after analyses are completed.