Mechanisms of overdose from unintentional fentanyl use when intending to use stimulants: a qualitative study of people who use stimulants and avoid opioids

Background As many as two-fifths of nonfatal opioid overdoses in San Francisco, CA are from unintentional fentanyl use, with most people intending to use stimulants. However, the mechanisms of fentanyl exposure are unclear. Objective To characterize mechanisms of unintentional fentanyl use resulting in non-fatal overdose among people who intend to use stimulants and not opioids. Methods We interviewed 17 people using stimulants and avoiding opioids who experienced an overdose attributed to unintentional fentanyl use between August 2023 and July 2024. Interviews were semi-structured and included questions about drug use practices, the events leading up to the most recent overdose, and ways participants protected themselves from fentanyl. Informed by the risk environment framework, we used an inductive coding approach to identify key themes, characterizing the social contexts and mechanisms of unintentional fentanyl use and non-fatal overdose. Results Participants reported using methamphetamine and cocaine in powder and rock/crack form and reported smoking, injecting, or intranasal use. We identified three distinct phases of drug use in which participants were exposed to fentanyl they thought to be a stimulant: procurement, storage, and consumption. Participants employed a range of practices to protect themselves from fentanyl, but their state of mind and social context created situations in which usual precautions were ineffective or not utilized. Structural factors, including inadequate housing, criminalization of sex work and drug use, and unpredictability in drug supply sources, contributed to overdose from unintentional fentanyl use. Conclusions We document multiple mechanisms of overdose from unintentional fentanyl use which may operate at individual, interpersonal, and/or structural levels. The complexity of the phenomenon, which cannot be fully explained by "contamination" of stimulants or any other single mechanism alone, suggests interventions are needed at multiple levels of the risk environment to prevent overdoses among people who use stimulants. A combination of policy changes to address structural factors and implementation of individual-level harm reduction practices is required to address overdose from unintentional fentanyl use.