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For the longitudinal study, Edison Manrique-Garcia, M.D., Ph.D., of the Karolinska Institutet in Stockholm and colleagues tracked the outcomes of 50,373 men aged 18 to 19, who completed a questionnaire on use of alcohol, tobacco, and other substances at the time of enlisting. Deceased cohort members up to age 60 were identified during the follow-up through the National Cause of Death Register, and overall mortality in the cohort was assessed according to information on the level of cannabis use obtained from the survey at conscription.
A total of 3,918 died during the 42 years of follow-up. Of those who died, 651 (17%) had reported cannabis use at conscription. Subjects with a baseline history of heavy cannabis use had a significantly higher risk of death (hazard ratio=1.4) than those without such a history. The authors found an excess mortality among subjects with psychotic disorders, but the level did not differ between those with a history of cannabis use (ever users: hazard ratio=3.8; heavy users: hazard ratio=3.8) and those without such a history (hazard ratio=3.7). No interaction effect was observed between cannabis use and diagnosis of psychotic disorders with regard to mortality.
“The study is convincing in its finding of increased mortality among those who used cannabis moderately to heavily prior to age 19,” A. Eden Evins, M.D., M.P.H., an associate professor of psychiatry at Harvard Medical School and director of the Massachusetts General Hospital Center for Addiction Medicine, told Psychiatric News. “It will be important now to better understand the causal pathway for the effect of early cannabis use on mortality, particularly whether it is through increased rates of cannabis addiction, which is far more common among those who initiate regular cannabis use in adolescence, other addictions such as alcohol or tobacco, or through other somatic illnesses such as cardiovascular or pulmonary disease,” said Evins, who was not involved in the Swedish study.
For related information, see the Psychiatric News article “Research Identifies Gene Linked to Cannabis-Induced Psychosis.”
(Image: iStock/nicole waring)