RESUMEN
Background: Polydrug use has been implicated in driving a "fourth wave" of the overdose crisis in North America, specifically through concurrent use of stimulants and opioids, especially fentanyl. In France, however, heroin has historically been and remains the easiest-to-access opioid, accounting for most drug treatment demand. Whether similar polydrug use is increasing in Western Europe remains understudied, despite severe health implications and potential inadequate public health responses.Methods: We take advantage of a nation-wide dataset containing information on all patients serviced in treatment centers in France from 2010 to 2020. We conduct Poisson regression to determine the main predictors of stimulant use among people who use heroin (PWUH) and opioids (PWUO) generally.Results: Heroin remains the primary opioid within drug treatment in France. A decreasing number of out-patients seeking treatment for heroin use has been accompanied by an increasing trend of stimulant use over time, most commonly with powder cocaine. Our results suggest a significant increase of crack cocaine use among the most vulnerable PWUH. Concurrent use of stimulants among PWUH was positively associated with use of alcohol, cannabis, unprescribed psychotropics and hallucinogens, and negatively with tobacco. Similar results were found for all in-treatment PWUO.Conclusions: Our results uncover heterogeneity in the profiles of PWUH that should be fully acknowledged to ensure better efficiency in substance use clinical practices and policy, while simultaneously drawing attention to trends in concurrent opioid-stimulant use outside North America. We advocate for an extension of the generalized risk framework and its implementation in prevention programs.