Among 9,583 Australian twins, all levels of cannabis involvement were associated with suicidal ideation, with the association persisting after accounting for other psychiatric disorders and substances.
Read this if you're concerned about the relationship between cannabis use and mental health risk.
ORs 1.28-2.00 for suicidal ideation across all cannabis use levels
What the researchers found
Researchers analyzed data from 9,583 individuals (58.5% female, aged 27-40) from the Australian Twin Registry, examining relationships between cannabis use levels and suicidal thoughts and behaviors. Cannabis involvement was categorized into four levels: no use, use only, 1-2 disorder symptoms, and 3+ symptoms.
All levels of cannabis involvement were associated with suicidal ideation (odds ratios 1.28-2.00), and these associations persisted after controlling for other psychiatric disorders and substance use. Cannabis involvement was also associated with unplanned (but not planned) suicide attempts.
Twin analyses revealed that shared genetic factors (correlation 0.45) and environmental factors (correlation 0.21) contributed to the overlap between cannabis involvement and suicidal ideation, suggesting the association is partly explained by common underlying vulnerabilities rather than a direct causal link.
Why it matters
Understanding the association between cannabis use and suicidality is important for clinical screening. The finding that shared genetic and environmental factors partially explain the link helps clinicians understand that cannabis use may be a marker of underlying vulnerability rather than a direct cause.
The numbers in context
9,583 individuals (58.5% female). All cannabis involvement levels associated with suicidal ideation (ORs 1.28-2.00). Genetic correlation: 0.45. Environmental correlation: 0.21. Cannabis associated with unplanned but not planned attempts.
How the study worked
Cross-sectional analysis of 9,583 twins from the Australian Twin Registry, aged 27-40. The Semi-Structured Assessment of the Genetics of Alcoholism (SSAGA) assessed cannabis involvement at four levels. Multinomial logistic regression and twin genetic analyses examined associations with suicidal ideation and attempts.
What this study cannot tell us
Cross-sectional design cannot determine temporal direction. Australian twin sample may not generalize to other populations. Self-reported data. The association is modest and substantially attenuated when controlling for confounders. Cannot distinguish effects of cannabis from correlated risk factors.
How to read the evidence
Large twin study with genetic analysis controlling for shared vulnerability. Cross-sectional design limits causal inference.
When this study was published
Published in 2015 using Australian Twin Registry data.
The bigger picture
The cannabis-suicidality association exists but is modest and partly explained by shared underlying factors. This nuanced finding helps move beyond simple "cannabis causes suicidality" claims toward a more sophisticated understanding of how substance use and mental health vulnerabilities overlap.
Questions still open
- Does the association between cannabis and suicidality differ by age of onset? Could the shared genetic factors be identified and used for screening? Is the link to unplanned attempts particularly concerning from a prevention standpoint?
Common questions
Does cannabis cause suicidal thoughts?
Should cannabis users be screened for suicidality?
Read the original research
The relationship between cannabis involvement and suicidal thoughts and behaviors.
Drug and alcohol dependence, 150, 98-104
Citation
Delforterie, M J; Lynskey, M T; Huizink, A C; Creemers, H E; Grant, J D; Few, L R; Glowinski, A L; Statham, D J; Trull, T J; Bucholz, K K; Madden, P A F; Martin, N G; Heath, A C; Agrawal, A. (2015). The relationship between cannabis involvement and suicidal thoughts and behaviors.. Drug and alcohol dependence, 150, 98-104. https://doi.org/10.1016/j.drugalcdep.2015.02.019
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