Among all the adverse outcomes associated with adolescent self-harm, weekly cannabis use at age 35 was the only one that remained independently associated after accounting for adolescent mental health, substance use, and antisocial behavior.
Read this if you want to understand the long-term relationship between teenage self-harm and adult cannabis use.
Weekly cannabis use at 35 was 2.3x more likely in those who self-harmed as teens, even after controlling for mental health
What the researchers found
In a population-based cohort of 1,671 Australians followed from adolescence to age 35, those who self-harmed during adolescence (8% of the cohort) had significantly worse outcomes across multiple domains: social disadvantage, mental health, and substance use.
Most of these associations were explained by concurrent adolescent mental health disorders and substance use. However, weekly cannabis use at age 35 uniquely survived all adjustments (adjusted OR 2.27, 95% CI 1.09-4.69). Even after controlling for adolescent depression, anxiety, antisocial behavior, and substance use, adolescent self-harm still independently predicted heavy cannabis use two decades later.
Other notable associations before full adjustment included daily smoking (OR 2.00), cannabis dependence (OR 2.67), and financial hardship (OR 1.88).
Why it matters
The finding that weekly cannabis use was the only outcome that remained independently associated with adolescent self-harm after exhaustive adjustment is striking. It suggests a specific pathway from self-harm to heavy cannabis use that operates independently of the mental health and behavioral problems typically blamed for both.
The numbers in context
Sample: 1,671 analyzed (135 self-harmers, 1,536 controls). Weekly cannabis use at 35: OR 3.18 after mental health adjustment, OR 2.27 after full adjustment (95% CI 1.09-4.69). Cannabis dependence: OR 2.67 before adjustment. Daily smoking: OR 2.00. Self-harm prevalence: 8%.
How the study worked
Prospective cohort study using the Victorian Adolescent Health Cohort Study (Australia). A stratified random sample of 1,943 adolescents from 44 schools was recruited starting in 1992 and followed through 2014. Self-harm was assessed across four adolescent waves (mean age 15.9). Outcomes at age 35 were analyzed using progressively adjusted logistic regression models.
What this study cannot tell us
Self-harm was self-reported. Weekly cannabis use at age 35 was a relatively small outcome, and the confidence interval for the adjusted association was wide (1.09-4.69). The study cannot determine the mechanism linking self-harm to later cannabis use. Attrition over 20 years of follow-up may introduce bias.
How to read the evidence
Population-based longitudinal cohort with 20 years of follow-up and progressive statistical adjustment. Strong design published in The Lancet Child & Adolescent Health.
When this study was published
Published in 2017. The unique persistence of the self-harm-cannabis association continues to be explored in developmental research.
The bigger picture
This study reframes the relationship between self-harm and substance use. Rather than both being symptoms of underlying mental illness, the independent persistence of the cannabis association suggests that self-harm in adolescence may specifically channel into cannabis use through pathways not captured by depression, anxiety, or conduct disorder diagnoses.
Questions still open
- What pathway connects adolescent self-harm to heavy cannabis use two decades later? Is cannabis used as self-medication for the psychological sequelae of self-harm? Would early intervention for self-harming adolescents reduce their later cannabis use?
Common questions
Why was cannabis use the only outcome that stayed significant?
Does self-harm cause cannabis addiction?
Read the original research
20-year outcomes in adolescents who self-harm: a population-based cohort study.
The Lancet. Child & adolescent health, 1(3), 195-202
Citation
Borschmann, Rohan; Becker, Denise; Coffey, Carolyn; Spry, Elizabeth; Moreno-Betancur, Margarita; Moran, Paul; Patton, George C. (2017). 20-year outcomes in adolescents who self-harm: a population-based cohort study.. The Lancet. Child & adolescent health, 1(3), 195-202. https://doi.org/10.1016/S2352-4642(17)30007-X
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