Modelling crack cocaine use trends over 10 years in a Canadian setting

Abstract

Introduction and aims: Crack cocaine use among illicit drug users is associated with a range of health and community harms. However, long-term epidemiological data documenting patterns and risk factors for crack use initiation remain limited especially among injection drug users. We investigated longitudinal patterns of crack cocaine use among polydrug users in Vancouver, Canada.

Design and methods: We examined the rate of crack use among injection drug users enrolled in a prospective cohort study in Vancouver, Canada between 1996 and 2005. We also used a Cox proportional hazards regression analysis to identify independent predictors of crack use initiation among this population.

Results: In total, 1603 injection drug users were recruited between May 1996 and December 2005. At baseline, 7.4% of participants reported ever using crack and this rate increased to 42.6% by the end of the study period (Mantel trend test P < 0.001). Independent predictors of crack use initiation during the study period included frequent cocaine injection, crystal methamphetamine injection, residency in the city's drug using epicenter and involvement in the sex trade (all P < 0.05).

Discussion and conclusions: These findings demonstrate a massive increase in crack use among injection drug users in a Canadian setting. Our findings also highlight the complex interactions that contribute to the initiation of crack use among injection drug users and suggest that evidence-based interventions are urgently needed to address crack use initiation and to address harms associated with its ongoing use.

Figure 1

Rate of daily crack cocaine use among a cohort of injection drug users in Vancouver, Canada over a 10 year period. Mantel test for trend: P < 0.01.

Figure 2

Time to crack use initiation stratified by residency in the downtown eastside, sex trade work and frequent cocaine use. Note: The n at the bottom of the figure panels reflect the number of individuals who remain at risk of initiating crack use over time. The diminishing number of participants at risk at each subsequent time interval is a result of events or limited follow up. The rapid increase in probability of crack use after approximately 6 months reflects the fact that individuals only returned for follow up after approximately 6 months.