In a cohort of 1,943 adolescents followed to age 29, cannabis use during adolescence was independently associated with a 2.4-fold increased risk of self-harm, alongside depression, anxiety, and alcohol use.
Read this if you work with at-risk adolescents or want to understand risk factors for self-harm.
2.4x increased self-harm risk associated with adolescent cannabis use
What the researchers found
A population-based cohort of 1,943 Australian adolescents was followed from age 15.9 to 29 with seven waves of assessment. Self-harm was reported by 8% during adolescence, with higher rates in girls (10%) than boys (6%).
During adolescence, incident self-harm was independently associated with depression and anxiety symptoms (HR 3.7), cannabis use (HR 2.4), high-risk alcohol use (HR 2.1), antisocial behavior (HR 1.9), and cigarette smoking (HR 1.8). Cannabis use remained a significant predictor after adjusting for all other risk factors.
Most self-harming behavior resolved spontaneously during the transition to adulthood. Adolescent depression and anxiety was the strongest predictor of continuing self-harm into young adulthood (HR 5.9).
Why it matters
Cannabis was identified as an independent risk factor for self-harm, separate from depression, anxiety, and other substance use. This has implications for suicide prevention: addressing cannabis use in at-risk adolescents may be an underappreciated component of self-harm prevention.
The numbers in context
1,943 adolescents, 7 waves, mean ages 15.9-29.0. Self-harm prevalence: 8% in adolescence. Cannabis HR: 2.4 (95% CI 1.4-4.4). Depression/anxiety: HR 3.7. Alcohol: HR 2.1. Most self-harm resolved spontaneously.
How the study worked
Population-based stratified random sample of 1,943 adolescents from 44 schools in Victoria, Australia. Seven waves of questionnaires and telephone interviews from mean age 15.9 to 29.0 years (1992-2008). Cox regression for risk factor identification.
What this study cannot tell us
Self-reported cannabis use and self-harm. Association does not prove causation. Confounding by personality traits, trauma, or other unmeasured factors is possible. Australian sample may not generalize globally.
How to read the evidence
Large population-based cohort published in The Lancet with long follow-up and multiple adjustment. Strong evidence for association, though causation cannot be definitively established.
When this study was published
Published in 2012. Cannabis as a risk factor for self-harm has been incorporated into clinical risk assessment frameworks since.
The bigger picture
Published in The Lancet, this study was influential in establishing cannabis use as a modifiable risk factor for self-harm. The finding that most self-harm resolves spontaneously but depression predicts persistence informed clinical prioritization.
Questions still open
- Would cannabis cessation reduce self-harm risk in at-risk adolescents? Does cannabis cause self-harm or does an underlying factor drive both? Should cannabis screening be part of suicide risk assessment?
Common questions
Does cannabis cause self-harm?
Does self-harm in teenagers usually continue into adulthood?
Read the original research
The natural history of self-harm from adolescence to young adulthood: a population-based cohort study.
Lancet (London, England), 379(9812), 236-43
Citation
Moran, Paul; Coffey, Carolyn; Romaniuk, Helena; Olsson, Craig; Borschmann, Rohan; Carlin, John B; Patton, George C. (2012). The natural history of self-harm from adolescence to young adulthood: a population-based cohort study.. Lancet (London, England), 379(9812), 236-43. https://doi.org/10.1016/S0140-6736(11)61141-0
Explore the wider topic
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