The use of diverted pharmaceutical opioids is associated with reduced risk of fentanyl exposure among people using unregulated drugs in Vancouver, Canada.

Background: Although non-medical use of pharmaceutical opioids (POs) is associated with a number of risks, in the context of the opioid-overdose crisis, it may have the secondary benefit of decreasing the risk of exposure to more potent opioids from unregulated sources. The aim of this study was to assess the effects of using diverted POs on fentanyl exposure.

Methods: Using data from two prospective community-recruited cohorts of people who use drugs (PWUD) in Vancouver, Canada, we estimated the independent relationship between using diverted POs and fentanyl exposure (assessed through urine drug test [UDT]) between 2016 and 2018. We also explored if participant characteristics modified this relationship.

Results: Over the study period, among 1150 participants, 241 (21.0%) reported using diverted POs in 292 (12.8%) occasions. In adjusted analyses, PWUD using diverted POs had decreased odds of fentanyl exposure (Adjusted odds ratio [AOR] = 0.70, 95% CI: 0.52-0.94). The reduced odds of fentanyl exposure persisted among participants with morphine positive UDT (AOR = 0.57, 95% CI: 0.40-0.82), but not among those with negative morphine UDT (AOR = 0.91, 95% CI: 0.54-1.55).

Conclusion: PWUD using diverted POs in our sample were 30% less likely to be exposed to fentanyl. This reduced likelihood was primarily observed among PWUD with morphine positive UDT, which could partially be explained by longer duration of action and lower street cost of slow-release oral morphine relative to other POs and fentanyl. Findings suggest that access to a regulated supply of pharmaceutical-grade opioids may serve to reduce fentanyl-related harms.