Mortality risk in a cohort of subjects reported by authorities for cannabis possession for personal use. Results of a longitudinal study.

OBJECTIVE: to study mortality risk in a cohort of cannabis consumers. DESIGN: longitudinal study on a cohort of 2,511 subjects reported to the Drug Addiction Control Force (DACF) for cannabis possession for personal use between 1990 and 2004 residents in the metropolitan area of Bologna. METHODS: to identify people already treated for drug dependence, the cohort was linked with the clinical archive of the public treatment centers for drug addiction (PTC) in the metropolitan area of Bologna and the results were separated into PTC clients (subjects in treatment at a PTC, all heroin users) and non-PTC clients (subjects not in treatment at a PTC, no knowledge regarding other illicit drugs being used besides cannabis). RESULTS: an excess of mortality was observed for all causes in the cohort compared to the general population, both among PTC clients (SMR 14.61 CI 95% 9.21-23.19) and non-clients (SMR 2.43 CI 95% 1.67-3.55). Among PTC clients the highest and most statistically significant SMRs were for overdose, suicide, and AIDS. Among non PTC clients there was an excess for traffic accidents and overdose. CONCLUSION: the results of the study show an elevated risk of death for consumers of cannabis, a percentage of which probably also consumed other substances, and a very few which presented themselves for treatment at a public drug treatment center.