How substance use preferences and practices relate to fentanyl exposure among people who use drugs in Rhode Island, USA

Background: Over 107,000 people died in the United States (U.S.) from drug overdose in 2022, with over one million overdose deaths since 1999. The U.S. drug market is characterized by a highly toxic, unregulated, and rapidly changing supply. Understanding the extent of exposure to fentanyl among people who use drugs (PWUD) will guide public health interventions aimed to decrease overdose. Methods: We utilized baseline data from the Rhode Island Prescription and Illicit Drug Study, a randomized controlled trial of harm reduction-oriented interventions for PWUD in Rhode Island from 2020 to 2023. We evaluated sociodemographic and drug use-related covariates and examined fentanyl presence in urine drug testing (UDT). We built a classification and regression tree (CART) model to identify subpopulations with the highest likelihood of fentanyl presence in UDT. Results: Among 446 participants, those with fentanyl present in UDT tended to be younger, non-Hispanic white, and had recently injected drugs (p<0.05 for all). The CART analysis demonstrated a large variation in sample sub-groups' likelihood of fentanyl presence in UDT, from an estimated probability of 0.09 to 0.90. Expected recent fentanyl exposure was the most important predictor of fentanyl in UDT. Conclusions: Univariate analyses and CART modeling showed substantial variation in the presence of fentanyl in UDT among PWUD. Harm reduction services for people actively injecting drugs and drug checking programs based on capacity-building, empowerment, and targeted towards those not yet engaged in services are urgently needed to support PWUD in navigating the current volatile drug supply.