Modeling Naloxone Response in Simulated Opioid-Xylazine Overdose Scenarios: A Public Health Simulation Study

In the United States, the overdose crisis has become a critical issue involving polysubstance combinations, especially with fentanyl mixed with xylazine, a non-opioid veterinary sedative not directly reversed by naloxone. This study addressed how xylazine involvement may affect simulated naloxone response in opioid-xylazine overdose scenarios. Using publicly available CDC/NCHS provisional drug overdose death counts from January 2019 to December 2024, national trends in overdose deaths involved with xylazine, fentanyl, and heroin were analyzed. Monthly changes in overdose deaths were estimated using a simple linear trend model, while theoretical recovery probability was estimated under different naloxone timing and xylazine-involvement conditions through an illustrative simulation model. There was an increase in xylazine-involved overdose deaths from 123 deaths in January 2019 to 6,079 deaths in December 2024. There was also an increase in fentanyl-involved deaths from 30,367 to 47,155 in the same time period. However, there was a decrease in heroin-involved deaths from 15,475 to 2,809 in the same study period. A strong upward trend was reported for xylazine deaths in the regression results, with an estimated increase of 104.6 deaths per month and R2=0.981. In the simulation, modeled opioid-only recovery probability increased to 1.00 with immediate naloxone administration. However, immediate-response recovery probability decreased to 0.80 with full xylazine involvement. In the same condition, delayed response recovery probability decreased to 0.56. These simulated findings suggest that naloxone remains important for suspected opioid overdose response. However, xylazine involvement may reduce theoretical recovery probability under the assumptions of the model.