Cannabis and suicide: longitudinal study

Background: Some studies suggest that cannabis use is associated with suicidal ideation, but no detailed longitudinal study has examined suicide as an outcome. Aims: To examine the association between cannabis use and completed suicide.

Method: A longitudinal study investigated 50087 men conscripted for Swedish military service, with cannabis use measured non-anonymously at conscription. Suicides during 33 years of follow-up were identified by linkage with the National Cause of Death Register.

Results: There were 600 (1.2% of cohort) suicides or deaths from undetermined causes. Cannabis use was associated with an increased risk of suicide (crude OR for 'ever use' 1.62, 95% CI 1.28-2.07), but this association was eliminated after adjustment for confounding (adjusted OR=0.88, 95% CI 0.65-1.20).

Conclusions: Although there was a strong association between cannabis use and suicide, this was explained by markers of psychological and behavioural problems. These results suggest that cannabis use is unlikely to have a strong effect on risk of completed suicide, either directly or as a consequence of mental health problems secondary to its use.