Initiation into heroin use among street-involved youth in a Canadian setting: A longitudinal cohort study.

Abstract

Emerging evidence suggests that non-medical prescription opioid (NMPO) use may be a risk factor for initiating heroin use; however, pathways from PO to heroin use among youth remain underexplored. We sought to examine the association between NMPO use and heroin initiation. Between September 2005 and June 2017 data were derived from an open prospective cohort of street-involved youth aged 14-28 who use illegal drugs in Vancouver, Canada. The study included 526 youth who had never used non-injection heroin, and 652 youth who had never used injection heroin at baseline. We used Cox proportional hazards regressions to examine the association between NMPO use - in addition to other substance use patterns - and subsequent initiation into non-injection and injection heroin use. Among those who had never used non-injection heroin at baseline, 133 (25.3%) initiated non-injection heroin use during the study period. Among those who had never injected heroin at baseline, 137 (21.0%) initiated heroin injection during the study period. In multivariable analyses, NMPO use, crack use, and crystal methamphetamine use predicted non-injection heroin initiation (all p < 0.05). In separate multivariable analyses, non-injection heroin and crystal methamphetamine predicted heroin injection initiation (all p < 0.05). Among street-involved youth in this setting, NMPO use predicted initiation into non-injection heroin use but not initiation into heroin injection. Interestingly, crack cocaine and crystal methamphetamine use were stronger predictors of heroin initiation than NMPO use was, suggesting that stimulant use may carry greater risks for heroin initiation than NMPO use.