Cannabis use at 16 predicted first suicide attempt by age 21 among at-risk adolescents | Research

The takeaway

Among teenagers who had suicidal thoughts or self-harmed, cannabis use was one of the strongest predictors of a first suicide attempt within the next five years.

Adolescent mental health clinicians, school counselors, parents of at-risk teens, and suicide prevention researchers.

OR 2.6 for suicide attempt

What the researchers found

Cannabis use at age 16 predicted first suicide attempt by 21 in both high-risk groups: OR 2.61 (95% CI 1.11-6.14) among those with suicidal thoughts and OR 2.14 (95% CI 1.04-4.41) among those with non-suicidal self-harm. Other key predictors included illicit drug use, sleep problems, and exposure to others' self-harm. Many commonly cited risk factors were NOT predictive.

Why it matters

Most adolescents with suicidal thoughts or self-harm will NOT attempt suicide. Identifying which few will is clinically crucial. This study shows cannabis use is one of the strongest markers, while many traditional risk factors failed to predict escalation.

The numbers in context

12% of each high-risk group (38/310 with suicidal thoughts, 46/380 with self-harm) attempted suicide by age 21. Cannabis OR 2.61 (suicidal thoughts group), OR 2.14 (self-harm group). Self-harm OR 2.78, illicit drugs OR 2.47.

How the study worked

Population-based birth cohort study (ALSPAC, UK) following 1,025 adolescents at elevated risk (456 with suicidal thoughts, 569 with self-harm at age 16) through age 21, using prospectively recorded risk factors and logistic regression.

What this study cannot tell us

Observational design cannot establish causality. Cannabis use may be a marker for other risk factors or self-medication for distress rather than a causal factor. UK birth cohort may not generalize globally. Self-reported measures.

How to read the evidence

Strong: population-based birth cohort with 5-year prospective follow-up.

When this study was published

Published in 2019.

The bigger picture

Clinicians assessing suicide risk in teenagers are often told to ask about many factors. This study narrows the field: substance use (especially cannabis), sleep problems, and exposure to self-harm are the factors that actually distinguish who will escalate from ideation to action.

Questions still open

Does reducing cannabis use in at-risk adolescents lower suicide attempt risk? Is cannabis a causal factor or a marker of underlying psychological distress?

Common questions

Does cannabis use increase suicide risk in teenagers?

In this prospective study, cannabis use at 16 was associated with approximately 2-2.6 times higher odds of a first suicide attempt by age 21, but the study cannot prove causation.

What other factors predicted suicide attempts?

Other strong predictors included other illicit drug use, non-suicidal self-harm, sleep problems, and exposure to friends or family who self-harmed.

Read the original research

Predictors of future suicide attempt among adolescents with suicidal thoughts or non-suicidal self-harm: a population-based birth cohort study.

The lancet. Psychiatry, 6(4), 327-337

View on PubMed ↗Publisher’s paper ↗

Citation

Mars, Becky; Heron, Jon; Klonsky, E David; Moran, Paul; O'Connor, Rory C; Tilling, Kate; Wilkinson, Paul; Gunnell, David. (2019). Predictors of future suicide attempt among adolescents with suicidal thoughts or non-suicidal self-harm: a population-based birth cohort study.. The lancet. Psychiatry, 6(4), 327-337. https://doi.org/10.1016/S2215-0366(19)30030-6