Project Summary: The United States substance use epidemic is one of the most significant health crises in history, having claimed the lives of more than 1 million Americans since 1999. Despite a significant literature on the epidemic, there is still much we do not know. This project will address two open questions. The first is to study the effects of enforcement interventions in prescription drug markets. Under the Controlled Substances Act (CSA), physicians, pharmacies, and pharmaceutical distributors who handle controlled substances have obligations to prevent diversion (i.e., illicit uses of controlled substances). In the case of opioids, a number of physicians, pharmacies, and pharmaceutical distributors were shut down or faced criminal charges due to violating their CSA obligations. The effects of these interventions on opioid supply and health are unknown. The proposed project will assemble new data on all federal enforcement interventions related to prescription opioids since the mid-2000s. These data will be supplemented with individual practitioner and firm-level data on opioid supply and used to construct a measure of exposure to enforcement interventions for all U.S. counties over time. Aim 1 will use time-series analysis to estimate the impact of enforcement interventions on county opioid supply. To study health, the project will use restricted-use vital statistics data from the National Center for Health Statistics (NCHS) to measure county overdose death rates. Aim 2 will use this data, along with the enforcement data and same methodology as aim 1, to estimate the impact of enforcement interventions on deaths from prescription opioids, illicit opioids, and all drugs. The second question this project will examine is what economic and social factors can explain continuously rising deaths from illicit opioids (i.e., heroin and illicitly manufactured fentanyl). Illicit opioid deaths have risen essentially continuously for ten years after policy began reducing prescription opioid supply. Aim 3 will examine two economic and social theories about why. The first theory is downward sloping illicit drug supply. This theory is that greater opioid use generated economies of scale in drug trafficking, and that this has reduced illicit opioid prices and increased use. The second theory is about thick markets. This theory is that greater illicit opioid use has increased people’s social interactions with illicit opioid users and sellers, and that these interactions have further increased illegal opioid use. The project will draw from the NCHS vital statistics data, along with a number of other datasets, to test how much each theory can explain rising illegal opioid deaths. Time-series regressions will be estimated at the county-level during the expansion of the opioid epidemic from prescription opioids to heroin (2006 to 2014) and from heroin to fentanyl (2010+). To test the thick markets theory, regressions will relate exogeneous increases in ill...