This community-based randomized controlled trial will test the effect of contingent financial rewards on smoking abstinence among homeless-experienced adult cigarette smokers. Participants will be recruited from 3 Boston Health Care for the Homeless Program locations: a shelter clinic, a day center clinic, and a medical center clinic. All participants will be offered a varenicline prescription and tobacco coaching. Incentive arm participants will receive escalating financial rewards for saliva cotinine levels <30 ng/ml, assessed 10 times over 12 weeks. Embedded qualitative interviews will explore the mechanisms of on-treatment and post-treatment effects of financial incentives on smoking abstinence in the context of homelessness.

People experiencing homelessness have a 3.5-fold higher prevalence of cigarette smoking in comparison to non-homeless people, contributing to 2-fold higher rates of lung cancer and 3- to 5-fold higher rates of tobacco-attributable death. Homeless smokers want to quit, but studies have not yet uncovered the optimal approach to help them do so. In an 8-week pilot randomized controlled trial (RCT) at Boston Health Care for the Homeless Program (BHCHP), we found that financial incentives for smoking abstinence were associated with 7-fold higher odds of brief smoking abstinence in comparison to a non-incentivized control condition. These results suggest that financial incentives are a promising approach for reducing smoking in this vulnerable population, but further investigation in a larger sample is needed to improve the duration of on-treatment abstinence, assess post-treatment effects, and better understand mechanisms of action and contextual factors that may influence treatment response.

To address the above gaps in evidence, we will conduct a community-based RCT of financial incentives for smoking abstinence among adult smokers at BHCHP. Recognized as a leader in homeless health care, BHCHP serves 12,000 currently and formerly homeless patients annually throughout greater Boston. We will randomize 180 participants recruited from 3 BHCHP sites: a shelter clinic, a day center clinic, and a medical center clinic. All participants will be offered 12 weeks of varenicline, 5 sessions of tobacco coaching, and 10 cotinine monitoring visits over a 12-week period. Participants randomized to the financial incentives arm (n=90) will receive escalating debit card payments (range $25-$70) at each monitoring visit for saliva cotinine levels <30 ng/ml. Control arm participants (n=90) will receive a fixed payment ($10) at each monitoring visit regardless of their saliva cotinine level. We will use an embedded-experiment mixed methods design, where qualitative ('qual') data collection is embedded within a larger quantitative ('QUAN') RCT with the following specific aims:

Aim 1. (QUAN) To determine the effect of the financial incentives intervention on cotinine-verified 7-day smoking abstinence at A) the end of treatment (12 weeks) and B) 12 weeks after treatment (24 weeks).

Hypotheses: Incentive arm participants will have significantly greater cotinine-verified 7-day smoking abstinence than control arm participants at A) 12 weeks and B) 24 weeks.

Aim 2. (qual) To assess why, how, and under what circumstances homeless smokers A) achieve abstinence in response to financial incentives and B) maintain abstinence after incentives are stopped.

Interviews with participants at A) 12 weeks (N=30) and B) 24 weeks (N=20) will examine cognitive ('why?'), procedural ('how?'), and contextual ('under what circumstances?') dimensions of their response to financial incentives to generate hypotheses about potential mechanisms for on-treatment and post-treatment effects and to inform modifications of the intervention for future use.

Inclusion Criteria:

• Age ≥18 years old
• Lifetime smoker of ≥100 cigarettes with current daily smoking of ≥5 cigarettes per day, verified by a saliva cotinine level of ≥30 ng/mL
• Ready to try quitting smoking within the next 3 months
• Proficient in English
• Currently or formerly homeless
• Have a primary care provider within BHCHP system

Exclusion Criteria:

• Unable to provide informed consent
• History of allergic reaction to varenicline
• Currently pregnant, planning to become pregnant, or breastfeeding
• Past-month suicidal ideation with plan or intent, or past 12-month history of suicidal behaviors or attempts
• Psychiatric hospitalization in the past 3 months

Due to the sensitive nature of the data and personal health information involved, we do not plan to share IPD.

From enrollment until end of study follow-up at 24 weeks.

Participant were asked whether they had experienced specific symptoms linked with varenicline use (e.g. abnormal dreams, headaches, nausea, vomiting, and suicidality) at each cotinine monitoring visit. Participants could also report adverse events at any other study visit or via phone call to study staff. For each AE reported, study staff assessed date of onset, level of severity, resolution status, expectedness, and relatedness to study protocol.

Various limitations led to lower than anticipated enrollment and limited statistical power. The COVID-19 pandemic substantially delayed study launch. Shortly after the initial launch, recruitment was halted and delayed again due to the recall and global shortage of varenicline (the study medication). Reductions in foot traffic at recruitment sites (due to COVID-19 and fluctuating local patterns of and responses to homelessness) led to slower rates of recruitment once the study was relaunched.