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

Background And Aims: In Great Britain, cannabis and tobacco are commonly used substances, both independently and together. Use of either substance is associated with mental health problems, but prevalence of co-use within these populations is unknown. We aimed to (1) estimate prevalence of cannabis use, frequency of use and routes of administration (ROA) among tobacco smokers and non-smokers and (2) investigate mental health problems among non-users, tobacco-only, cannabis-only and co-users of both substances.

Design: Cross-sectional national on-line survey (Action on Smoking and Health) fielded in February-March 2020.

Setting: Great Britain.

Participants: Adults in Great Britain aged ≥ 18 years (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, self-reported treatment for mental health disorders (depression, anxiety and any). Statistically weighted prevalence estimates were computed to ensure representativeness. Correlates were assessed using χ tests and logistic regression.

Findings: In Great Britain in 2020, 7.1% of the sample had used cannabis in the past year. Tobacco smokers had greater odds of using cannabis in the past year (21.9%) and using cannabis daily (8.7%) than non-smokers [past-year: 4.7%; adjusted odds ratio (aOR) = 10.07, 95% confidence interval (CI) = 8.4-12.0; daily: 0.7%; aOR = 24.6, 95% CI = 18.0-33.6)]. Co-administration with tobacco was common (46.2% of non-smokers, 80.8% of tobacco smokers). Co-users reported the highest prevalence of any treatment for mental health problems (54.2%) in comparison to cannabis-only (45.8%), tobacco-only (33.2%) and non-users (22.7%; all P ≤ 0.05).

Conclusion: Approximately one in 13 adults in Great Britain reports having used cannabis in the past year, approximately four times as many among cigarette smokers as non-smokers. Co-administration of cannabis and tobacco, via smoking, appears to be common, including among self-identified non-smokers. Mental health problems appear to be particularly common among dual users.