Classification of patterns of tobacco and cannabis co-use based on temporal proximity: A qualitative study among young adults

Co-use of tobacco and cannabis is a common and complex behavior. The lack of harmonized measures of co-use yields confusion and inconsistencies in synthesizing evidence about the health effects of co-use. We aimed to classify co-use patterns based on temporal proximity and describe preferred products and motives for each pattern in order to improve co-use surveillance. We conducted semi-structured interviews in a sample of 34 young adults (Mage = 22.8 years, 32.4 % female) during 2017–2019 in California, USA. We employed a qualitative thematic analysis to identify timing, reasons, and contexts for tobacco and cannabis co-use and classify co-use patterns. Four emergent patterns of co-use with increasing temporal proximity between tobacco use and cannabis use were: Same-month different-day co-use (Pattern 1); Same-day different-occasion co-use (Pattern 2); Same-occasion sequential co-use (Pattern 3); and Same-occasion simultaneous co-use (Pattern 4). Participants used various product combinations within each pattern. Similar motives for all patterns were socialization, product availability, and coping with stress/anxiety. Unique motive for temporally distant patterns (Patterns 1 and 2) was seeking substance-specific effects (e.g., stimulant effect from nicotine, relaxation effects from cannabis), while unique motives for temporally close patterns (Patterns 3 and 4) were seeking combined effects from both substances (e.g., more intense psychoactive effects, mitigating cannabis adverse effects) and behavioral trigger (e.g., cannabis use triggers tobacco use). Our classification of co-use patterns can facilitate consistency for measuring co-use and assessing its health impacts. Future research should also measure product types and motives for different patterns to inform intervention efforts.