Determining the impact of cannabis use and severity on tobacco cessation outcomes: study protocol for a prospective tobacco treatment trial

BACKGROUND: Several evidence-based tobacco cessation treatment strategies exist, though significant barriers to cessation remain which must be addressed to improve abstinence rates for sub-populations of those smoking cigarettes. Cannabis co-use among those who use tobacco is common and appears to be increasing among adults in the United States (US). The literature evaluating the impact of cannabis use on tobacco cessation has been mixed and has several important limitations, which precludes development of treatment recommendations specific to individuals who use tobacco and co-use cannabis. To date, no prospective studies have evaluated the impact of cannabis use and severity on tobacco cessation or quantified cannabis use changes during tobacco treatment to assess for concurrent reductions, abstinence, or compensatory (i.e., increased) cannabis use. This study’s aims are to: (1) evaluate tobacco cessation outcomes among participants who co-use cannabis compared to participants only using tobacco, (2) using daily diaries and biochemical verification, assess changes in cannabis use during tobacco treatment, and (3) assess for a dose-dependent impact of cannabis use on tobacco cessation. METHOD: A multi-site, prospective, quasi-experimental 12-week tobacco treatment trial enrolling treatment-seeking adults (ages 18–40; N = 208) from three sites across South Carolina (US) who use tobacco daily and oversampling (2:1) those who co-use cannabis. Participants receive tobacco cessation pharmacotherapy (varenicline) paired with behavioral support, while cannabis use is not addressed as part of treatment. The primary outcome is 7-day point prevalence tobacco abstinence at the week 12 end of treatment visit, measured via biochemical verification and self-report. Secondary outcome measures include changes in cannabis use (via biochemical verification and self-report) during tobacco cessation treatment. DISCUSSION: Results from this trial have the potential to inform tobacco treatment among those co-using cannabis, which may require a tailored approach to address the role of cannabis in quitting tobacco. TRIAL REGISTRATION: The trial is registered with ClinicalTrials.gov: NCT04228965. January 14th, 2020.