13-Year Study Found Cannabis Linked to Suicidal Behavior but Not Depression
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- Frequent cannabis users had 2.9x higher risk of suicide attempts but no increased depression
- Evidence Grade:
- This is a well-powered population-based longitudinal study with long follow-up, providing moderate evidence for the association, though causation cannot be established.
- Study Age:
- Published in 2008. Subsequent research has continued to find associations between cannabis use and suicidality, with the depression question remaining debated.
- Original Title:
- Does cannabis use lead to depression and suicidal behaviours? A population-based longitudinal study.
- Published In:
- Acta psychiatrica Scandinavica, 118(5), 395-403 (2008)
- Authors:
- Pedersen, W
- Database ID:
- RTHC-00326
Evidence Hierarchy
Follows a group of people over time to track how outcomes develop.
What do these levels mean? →Frequently Asked 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.
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Cite This Study
https://rethinkthc.com/research/RTHC-00326APA
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
MLA
Pedersen, W. "Does cannabis use lead to depression and suicidal behaviours? A population-based longitudinal study.." Acta psychiatrica Scandinavica, 2008. https://doi.org/10.1111/j.1600-0447.2008.01259.x
RethinkTHC
RethinkTHC Research Database. "Does cannabis use lead to depression and suicidal behaviours..." RTHC-00326. Retrieved from https://rethinkthc.com/research/pedersen-2008-does-cannabis-use-lead
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.