Abstract There is growing research to suggest that law enforcement efforts to disrupt the illicit drug supply might inadvertently increase the number of overdose events in the surrounding community. When illicit substances are removed from a community, those who have a chemical dependency to those seized substances and familiarity with a known substance seller, may shift to alternative substances or dealers. The content of new substances may be unknown, putting people who use drugs at risk of overdose. Fatal relapse following abstinence has been identified as a risk factor among those leaving rapid detoxification programs, as well as incarceration settings, with no medication follow-up; this same effect occurs when a drug market is interrupted by law enforcement drug seizures. Studies have demonstrated this using statewide, aggregated, monthly time series data which limits causal inference. The overarching goal of this research project is to assess the potential unintended effects of drug policing policies by examining when seizures increase the likelihood of overdose. To do this, researchers will use street-level data to examine whether law enforcement drug market disruption of specific substances (e.g., methamphetamine, cocaine, heroin, fentanyl) impacts fatal or nonfatal overdose events in the surrounding area and where there are the opportunities to intervene. In addition to this, researchers will engage with people who use drugs, public health officials, and law enforcement to understand drug seizure processes and opportunities for mitigating harm. Researchers will accomplish study goals through four primary aims. The first (1) will examine the association between law enforcement drug market disruption and overdose by comparing drug seizure property room data from a police department in a large metropolitan jurisdiction to fatal and nonfatal overdose data. The second (2) will develop a database of drug seizure events reported by media sources and compare this database to police property room data. The third (3) will determine the extent to which local media sources can serve as drug seizure event data in the absence of police property room data as a generalizable methodology for other jurisdictions to track associations between drug seizures and overdose. The fourth (4) will assess feedback from law enforcement and public health officials about drug seizure processes and public health responses and include first-hand experiences of people who use drugs such that opportunities for intervention can be identified.