BackgroundUnsolicited Reporting Notifications(URNs) have been a component of Maryland’s Prescription Drug Monitoring Program (PDMP) since 2016. We evaluated the effect of URNs on providers’ prescription behaviors. MethodsThis is a quasi-experimental study of providers who were issued at least one URN from January 2018 to April 2021. Providers for whom URNs were not successfully delivered were designated as a comparison group. The outcome variables were average daily opioid and benzodiazepine prescriptions, average morphine milligram equivalents per patient, and proportion of overlapping opioid and benzodiazepine, either with or without muscle relaxant prescriptions. Changes were compared before versus after the issuance of a URN among the intervention and comparison groups using “Generalized Estimation Equation” and “Generalized Linear” Models. We also conducted stratified analyses by types of URN, including notifications for multiple provider episodes (MPE), overdose fatality (ODF), and dangerous drug combinations (DDC). ResultsThe average daily number of opioids prescriptions (3.3% decrease in the intervention group vs 22.7% increase in the comparison group, P<0.001), co-prescription of opioids and benzodiazepines either with muscle relaxants (68.0% decrease vs. 36.1% decrease, P<0.001), or without muscle relaxants (6.0% decrease vs. 16.3% increase, P<0.001), significantly reduced after the first URN regardless of the type of URN. Stratified analysis by types of URNs showed that ODF and DDC URNs had a significant effect on most of the outcomes of interest. ConclusionThe findings suggest that unsolicited reporting, especially particular types of URNs including ODF and DDC, is associated with subsequent changes in unsafe prescribing behaviors.