13-Year Study Found Cannabis Linked to Suicidal Behavior but Not Depression | Research

The takeaway

Following 2,033 Norwegians from their teens to late twenties, cannabis use was not associated with later depression, but frequent use in one's twenties was linked to nearly triple the risk of suicide attempts.

Read this if you want to understand the specific mental health risks associated with cannabis use beyond depression.

Frequent cannabis users had 2.9x higher risk of suicide attempts but no increased depression

What the researchers found

This population-based longitudinal study followed 2,033 Norwegians over 13 years from early adolescence to their late twenties.

Cannabis use in early adolescence showed no associations with later depression or suicidal behaviors. However, cannabis use in participants' twenties was significantly associated with suicidal ideation and suicide attempts.

The strongest finding emerged for frequent users: those who used cannabis 11 or more times in the past year had an adjusted odds ratio of 2.9 (95% CI: 1.3-6.1) for later suicide attempts, even after controlling for confounding factors.

Notably, the study found no independent association between cannabis and depression, suggesting the link to suicidal behavior may operate through pathways other than mood disorders.

Why it matters

This study separated two commonly conflated outcomes: depression and suicidal behavior. The finding that cannabis was linked to suicide attempts but not depression challenges the assumption that cannabis causes depression which then leads to suicidality, suggesting a more direct or alternative pathway.

The numbers in context

2,033 participants followed for 13 years. Frequent cannabis use (11+ times/year): OR 2.9 (95% CI: 1.3-6.1) for later suicide attempts after adjusting for confounders. No association with depression.

How the study worked

Prospective longitudinal study using the Young in Norway cohort. 2,033 participants were followed from early teens to late twenties over 13 years. Cannabis use, depression, suicidal ideation, and suicide attempts were assessed with adjustment for potential confounders.

What this study cannot tell us

Observational design cannot prove causation. Self-reported cannabis use and suicidal behavior may be unreliable. Confounders may not be fully controlled despite adjustment. The specific pathways linking cannabis to suicidality were not identified.

How to read the evidence

This is a well-powered population-based longitudinal study with long follow-up, providing moderate evidence for the association, though causation cannot be established.

When this study was published

Published in 2008. Subsequent research has continued to find associations between cannabis use and suicidality, with the depression question remaining debated.

The bigger picture

This study contributed to a nuanced understanding of cannabis-mental health associations. The specificity of the finding (suicidality but not depression) suggests that cannabis may affect risk through mechanisms other than mood, possibly through impulsivity, social isolation, or other behavioral pathways.

Questions still open

Through what non-depressive mechanism might cannabis increase suicide risk? Is there a threshold of use below which no association exists? Does the timing of use (adolescence vs. adulthood) modify the risk?

Common questions

Does cannabis cause suicidal thoughts?

This study found an association between frequent cannabis use and later suicide attempts, but it cannot prove causation. It's possible that shared risk factors or reverse causation explain the link.

Why wasn't cannabis linked to depression?

The study found no independent association after controlling for confounders. This suggests that while cannabis users may report more depressive symptoms in some studies, the relationship may be explained by other factors rather than a direct causal effect.

Read the original research

Does cannabis use lead to depression and suicidal behaviours? A population-based longitudinal study.

Acta psychiatrica Scandinavica, 118(5), 395-403

View on PubMed ↗Publisher’s paper ↗

Citation

Pedersen, W. (2008). Does cannabis use lead to depression and suicidal behaviours? A population-based longitudinal study.. Acta psychiatrica Scandinavica, 118(5), 395-403. https://doi.org/10.1111/j.1600-0447.2008.01259.x