The Impact of Benzodiazepine Use on Mortality Among Polysubstance Users in Vancouver, Canada

Objective. Illicit drug use is a well-established risk factor for increased morbidity and mortality. However, little is known about the impact of benzodiazepine use on mortality among populations of polysubstance users. This study aimed to identify the effect of benzodiazepine use on mortality among a prospective cohort of people in Canada who inject drugs (PWID). Methods. A cohort of PWID in Vancouver, Canada, was prospectively followed from May 1996 through November 2013. Data on participants were linked to the provincial vital statistics registry to ascertain mortality rates and causes of death. Multivariable extended Cox regression with time-dependent variables was used to investigate the relationship between benzodiazepine use and time to all-cause mortality. Results. During the study period, 2,802 participants were followed for a median of 67 months (interquartile range: 25-107). In total, 527 (18.8%) participants died, for an incidence density of mortality of 2.9 (95% confidence interval [CI] 2.7, 3.2) deaths per 100 person-years. After adjusting for HIV infection and other potential confounders, benzodiazepine use was independently associated with increased all-cause mortality (adjusted hazard ratio = 1.86, 95% CI 1.38, 2.51) and had a higher risk for mortality than all other traditional substances of abuse among this population. Results were consistent when non-overdose mortality was considered. Conclusion. In this setting, benzodiazepine use was more strongly associated with mortality than any other substance of abuse. Greater recognition of the safety concerns related to benzodiazepines and strategies to prevent diversion to illicit use are needed.