Depression in adolescence predicted later weekly cannabis use, but cannabis-suicidal ideation link was explained by other substance use | Research

The takeaway

In a longitudinal study of 1,606 adolescents, depression at age 15 predicted weekly cannabis use at 17, while the apparent link between cannabis and suicidal ideation was fully explained by concurrent alcohol, tobacco, and other drug use.

Parents, mental health professionals, researchers studying adolescent substance use

Depressed 15-year-olds were 2.3x more likely to use cannabis weekly by age 17

What the researchers found

Depression at age 15 predicted weekly cannabis use at age 17 (OR = 2.30, 95% CI: 1.19-4.43), even after adjusting for other substance use. Weekly cannabis use at 15 was initially associated with suicidal ideation at 17 (OR = 2.19, 95% CI: 1.04-4.58), but this association disappeared after controlling for other substance use.

Why it matters

This study helps untangle the direction of the cannabis-depression relationship, suggesting depression may drive cannabis use rather than the reverse, and that polysubstance use complicates simple causal narratives.

The numbers in context

Weekly cannabis use: 7.0% at age 15, rising to 15.6% by age 20. Weekly users were 11-15 times more likely to continue using over time. Depression predicting cannabis: OR = 2.30. Cannabis-suicidal ideation link (before adjustment): OR = 2.19.

How the study worked

Population-based cohort of 1,606 adolescents from Quebec followed from 1997, with cross-lagged analyses examining the direction of associations between cannabis use frequency, depressive symptoms, and suicidal ideation at ages 15, 17, and 20.

What this study cannot tell us

Quantity of cannabis consumed was not measured; self-reported data; Quebec-specific population may limit generalizability; observational design cannot fully establish causation.

How to read the evidence

Large population-based longitudinal cohort with cross-lagged analysis, though observational design limits causal inference.

When this study was published

Published in 2020.

The bigger picture

The finding that depression precedes cannabis use rather than the reverse challenges assumptions that cannabis causes depression. Meanwhile, the polysubstance context of suicidal ideation risk underscores that cannabis rarely operates in isolation.

Questions still open

Are depressed adolescents using cannabis as self-medication? Would earlier treatment of depression reduce subsequent cannabis use?

Common questions

Does this study show cannabis causes depression?

The opposite direction was supported: depression at earlier time points predicted later cannabis use, not the other way around. The findings suggest depressed adolescents may be more likely to start using cannabis regularly.

Does weekly cannabis use increase suicide risk?

An initial association was found, but it disappeared after accounting for concurrent alcohol, tobacco, and other drug use. The suicidal ideation risk appears tied to polysubstance use patterns rather than cannabis specifically.

Read the original research

Cannabis use, depression and suicidal ideation in adolescence: direction of associations in a population based cohort.

Journal of affective disorders, 274, 1076-1083

View on PubMed ↗Publisher’s paper ↗

Citation

Bolanis, Despina; Orri, Massimiliano; Castellanos-Ryan, Natalie; Renaud, Johanne; Montreuil, Tina; Boivin, Michel; Vitaro, Frank; Tremblay, Richard E; Turecki, Gustavo; Côté, Sylvana M; Séguin, Jean R; Geoffroy, Marie-Claude. (2020). Cannabis use, depression and suicidal ideation in adolescence: direction of associations in a population based cohort.. Journal of affective disorders, 274, 1076-1083. https://doi.org/10.1016/j.jad.2020.05.136