PISC Leaders Sara Solomon, MPH and Douglas Wiebe, PhD engaged mathematicians to lead a collaborative study, led by PISC Visiting Scholar Joanna Wares PhD, and informed locally by Safehouse and the Philadelphia Department of Public Health, to look at the movement of opioid users to an overdose prevention site. Overdose prevention sites, also known as safe injection facilities, are a proposed harm reduction strategy for targeting the rising rate of fatal opioid overdose and other substance use disorders. These sites face skepticism around their introduction and location, making this study very timely in presenting evidence for their beneficial impact. After developing a discrete-time, stochastic, mathematical model for user behavior, the study used it to simulate the effect of placing a site in the Kensington neighborhood in Philadelphia. The study found that placing the site in Kensington led to disproportionate benefits for white users, and that direct effects from overdose reversal in the overdose prevention site were small. However, fatalities and nonfatal overdoses were predicted to decrease substantially when indirect effects like site safety and user education were considered. These results imply the power of mathematical modeling in quantifying the impact of opioid prevention sites, which could help solidify such sites' place as a useful harm reduction strategy.