INTRODUCTION Tobacco and cannabis co-use is common but the two are rarely co-assessed or co-treated. We present a mixed methods study of UK young adults which aims to explore co-use and quitting behaviors.

METHODS This sequential explanatory mixed methods study used the Capability, Opportunity and Motivation - Behavior model to design a survey and interview schedule comprising elements of the Theoretical Domains Framework. The survey investigated tobacco and cannabis co-use, attitudes toward and experiences of quitting behaviors within Further Education students aged 16-30 with recent use of tobacco and cannabis. Chi-square and t-tests explored differences between substances in quitting behaviors. Survey respondents were invited to an interview to further explore beliefs and experiences of co-use and quitting.

RESULTS 141 participants responded to the survey, and 18 participated in an interview. 40% used tobacco daily and 21% used cannabis daily or almost daily. Most (86.5%) had made some effort to quit or reduce their use of tobacco and/or cannabis in the past six months but few used any formal support to do so. Quitting one was significantly associated with quitting the other ( = 0.01). Motivation to quit tobacco was significantly higher than cannabis (t=7.38,  = 0.01). Gaps in capability and opportunity to quit were identified. Co-use intervention opportunities are suggested.

CONCLUSIONS Few young adults used formal support when quitting tobacco or cannabis, and motivation to quit varied between tobacco and cannabis although quitting one substance was associated with quitting the other. Opportunities to quit or reduce harmful use of either or both are required.