Cannabis use and co-use in tobacco smokers and non-smokers: prevalence and associations with mental health in a nationally representative sample of adults in Great Britain, 2020

Background and aims: Cannabis and tobacco use is common in Great Britain. Use of both substances has been associated with mental health problems, but prevalence of their co-use and implications on mental health are unknown. We aimed to 1) estimate prevalence of cannabis use, frequency of use and routes of administration (ROA) among smokers and non-smokers; 2) to investigate mental health problems amongst non-users, tobacco-only, cannabis-only and co-users of both substances. Design: National online survey fielded in February–March 2020. Setting: Great Britain Participants: Adults in Great Britain aged ≥ 18 year (n = 12,809) Measurements: Tobacco use status (smoker [daily or non-daily] or non-smoker [never or ex-smoker]), cannabis use frequency (never to daily), detailed ROAs of cannabis, mental health disorders (depression, anxiety, and any). Weighted prevalence estimates were computed and correlates assessed using chi-squared tests and logistic regression. Findings: In Great Britain in 2020, 7.1% of British adults had used cannabis in the past year. Tobacco smokers has greater odds of using cannabis in the past year (21.9%) and using cannabis daily (8.7%) than non-smokers (past-year: 4.7%; aOR=10.07, [95% CI: 8.4 -12.0]; daily: 0.7%; aOR=24.6, [95% CI: 17.96-35.55]). Co-administration with tobacco was common (46.2% of non-smokers, 80.8% of smokers). Co-users reported the highest prevalence of any mental health problem (54.2%) in comparison to cannabis-only (45.8%), tobacco-only (33.2%) and non-users (22.7%; all p≤0.05). Conclusion: In a representative sample of Great Britain in 2020, tobacco smokers and non-smokers show significant exposure to combusted smoke and tobacco smoke. Self-identified non-smokers who regularly consume combusted cannabis, and smoked cannabis with tobacco warrant further attention. Co-use was associated with greater daily cannabis use, co-administration and mental health problems. Cannabis users should be considered a vulnerable population where rates of tobacco smoking are much higher than in the general population.