Effect of witnessing an overdose on the use of drug checking services among people who use illicit drugs in Vancouver, Canada

Background: Since 2013, fentanyl-contaminated drugs have been driving North America's opioid-overdose epidemic. Drug checking, which enables people who use illicit drugs (PWUD) to test and receive feedback regarding the contents of their drugs, is being considered as a potential tool to address the toxic drug supply. While some PWUD witness overdoses, little is known about the impact of these experiences on subsequent risk reduction practices. Objective: The purpose of this study was to examine the effect of witnessing an overdose on drug checking service use. Methods: Data were derived from prospective cohorts of PWUD in Vancouver, Canada, a setting with a community-wide fentanyl overdose crisis, between June 1, 2018 and December 1, 2018. Multivariable logistic regression was used to estimate the effect of witnessing an overdose on drug checking service use. Results: 1,426 participants were eligible for the study, including 530 females; 767 (53.8%) participants reported witnessing an overdose and 196 (13.7%) reported using drug checking services in the last 6 months. In multivariable analyses, after adjusting for a range of confounders including the use of fentanyl, witnessing an overdose was positively associated with drug checking service use (adjusted odds ratio = 2.32; 95% confidence interval: 1.57-3.49). Conclusion: Our findings suggest that witnessing an overdose may motivate PWUD to use drug checking services. Given that only a small proportion of PWUD in the study reported using drug checking services, our findings highlight the need to continue to scale-up a range of overdose prevention interventions.