Abstract
BACKGROUND: Observational studies consistently report associations between tobacco use, cannabis use and mental illness. However, the extent to which this association reflects an increased risk of new-onset mental illness is unclear and may be biased by unmeasured confounding.
METHODS: A systematic review and meta-analysis (CRD42021243903). Electronic databases were searched until November 2022. Longitudinal studies in general population samples assessing tobacco and/or cannabis use and reporting the association (e.g. risk ratio [RR]) with incident anxiety, mood, or psychotic disorders were included. Estimates were combined using random-effects meta-analyses. Bias was explored using a modified Newcastle-Ottawa Scale, confounder matrix, E-values, and Doi plots.
RESULTS: Seventy-five studies were included. Tobacco use was associated with mood disorders (K = 43; RR: 1.39, 95% confidence interval [CI] 1.30-1.47), but not anxiety disorders (K = 7; RR: 1.21, 95% CI 0.87-1.68) and evidence for psychotic disorders was influenced by treatment of outliers (K = 4, RR: 3.45, 95% CI 2.63-4.53; K = 5, RR: 2.06, 95% CI 0.98-4.29). Cannabis use was associated with psychotic disorders (K = 4; RR: 3.19, 95% CI 2.07-4.90), but not mood (K = 7; RR: 1.31, 95% CI 0.92-1.86) or anxiety disorders (K = 7; RR: 1.10, 95% CI 0.99-1.22). Confounder matrices and E-values suggested potential overestimation of effects. Only 27% of studies were rated as high quality.
CONCLUSIONS: Both substances were associated with psychotic disorders and tobacco use was associated with mood disorders. There was no clear evidence of an association between cannabis use and mood or anxiety disorders. Limited high-quality studies underscore the need for future research using robust causal inference approaches (e.g. evidence triangulation).
| Original language | English |
|---|---|
| Pages (from-to) | 1-15 |
| Number of pages | 15 |
| Journal | Psychological Medicine |
| Volume | 54 |
| Issue number | 15 |
| Early online date | 2 Dec 2024 |
| DOIs | |
| Publication status | Published - 31 Dec 2024 |
Data Availability Statement
Data and R code for the analyses included in this study have been provided online at https://github.com/chloeeburke/tobcanmeta.Funding
This work was supported by a Ph.D. studentship awarded to C. B. by the Society for the Study of Addiction. The funder of the study had no role in study design, data collection, data analysis, data interpretation, writing of the report, or decision to submit the article for publication. G. M. J. T. has previously received funding from Grand (Pfizer) for work not related to this project. C. B., H. S., and R. E. W. have completed paid consultancy work for Action on Smoking and Health (ASH) for work related to this project. The remaining authors have no relevant competing interests to declare.
Keywords
- anxiety disorders
- cannabis
- causal inference
- confounding
- epidemiology
- mood disorders
- psychotic disorders
- systematic review
- tobacco
ASJC Scopus subject areas
- Applied Psychology
- Psychiatry and Mental health
