Changes in the unregulated opioid drug supply during income assistance payment weeks in Vancouver, Canada: An exploratory analysis

BACKGROUND: Increased drug-related harms, including overdoses (poisonings), have been reported in the days around income assistance payments, yet little is known about changes in the unregulated drug supply during this time. In this exploratory analysis, we investigated whether changes in the unregulated opioid drug supply are associated with income assistance payment weeks. METHODS: Using data from drug checking services in Vancouver, BC, we conducted modified Poisson and linear regression models to examine the association between income assistance payment weeks and three key outcomes: (1) proportion of fentanyl positivity among expected opioid samples, (2) fentanyl concentration among fentanyl-positive expected opioid samples, and (3) proportion of benzodiazepine positivity among expected opioid samples. RESULTS: Between October 2017 and December 2019, 4306 (90.41%) of expected opioid samples tested positive for fentanyl, and the median fentanyl concentration was 7.0% (quartile [Q]1 – Q3: 5.1% – 9.8%). Income assistance payment week was associated with an increased prevalence of fentanyl positivity among expected opioid samples (prevalence ratio [PR]: 1.03; 95% confidence interval [CI]: 1.00, 1.05); however, we failed to find a statistically significant association between income assistance payment week and fentanyl concentration (regression coefficient: 0.70; 95% CI: 0.44, 1.09). Additionally, income assistance payment week was associated with an increased prevalence of benzodiazepine positivity among expected opioid samples (PR: 1.86; 95% CI: 1.07, 3.24). CONCLUSION: These findings suggest that during income assistance payment weeks, there may be more fentanyl and benzodiazepines circulating in the unregulated opioid drug supply. The rise in fentanyl and benzodiazepine-adulterated opioids during income assistance payment weeks may be contributing to the increase in illicit drug overdoses seen during this time of the month.