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 50 087 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.