Fentanyl concentrations in unregulated opioids and the blood of drug toxicity decedents

Abstract Fentanyl toxicity is the leading cause of unnatural death in British Columbia (BC), Canada, driven in part by fentanyl’s potency and unpredictable, highly variable concentration in unregulated drug samples. This study aims to identify emerging trends and the possible relationship between fentanyl concentrations in community drug samples and the postmortem blood of drug-toxicity decedents. Data for this ecological study were derived from Vancouver, BC community drug-checking sites and the BC Coroners Service. We analyzed fentanyl concentrations of opioid drug-checking samples alongside postmortem blood fentanyl concentrations from unintentional drug-toxicity decedents in which fentanyl contributed. The study period was January 2018 through December 2022. Monthly median fentanyl concentrations of drug-checking samples were compared to postmortem blood concentrations using generalized additive models. The primary time-series model, adjusted for potential confounders, did not identify a statistically significant association between drug-checking and postmortem concentrations (edf = 3.58, χ2 = 8.48, P = 0.104); however, a sensitivity analysis excluding extreme values revealed a significant nonlinear association (edf = 3.91, χ2 = 11.71, P = 0.038). Fentanyl concentrations in both the unregulated drug supply and postmortem blood changed over time with the two being mutually associated: as median fentanyl concentrations in opioid drug-checking samples increased, postmortem blood fentanyl concentrations generally decreased. Further research into complexities of the drug supply, changing substance use patterns, and rates of fentanyl exposure among opioid-naïve individuals may explain this nonlinear trend and inform strategies to abate the ongoing crisis.