Implications of county-level variation in U.S. opioid distribution.

BACKGROUND: Prescription opioids accounted for the majority of opioid-related deaths in the United States prior to 2010, and continue to contribute to opioid misuse and mortality. We used a novel dataset to investigate the distributional patterns of prescription opioids, whether opioid pill volume was associated with opioid-related mortality, and whether early state Medicaid expansions were associated with either pill volume or opioid-related mortality. METHODS: Data on opioid shipments to retail pharmacies for 2006-2013 were obtained from the U.S. Drug Enforcement Administration, and opioid-related deaths (ORDs) were obtained from the Centers for Disease Control and Prevention. We first compared characteristics of counties in the highest and lowest quartiles for per capita pill volume (PCPV). We used adjusted difference-in-differences regression models to identify factors associated with PCPV or ORDs, and whether early state Medicaid expansions were associated with either outcome. All models were estimated as linear regressions with standard errors clustered by county, and weighted by county population. RESULTS: We found large geographic variations in opioid distribution, and this variation appears to be driven by differences in demographics, healthcare access, and healthcare supply. In adjusted models, a one-pill increase in PCPV was associated with a 0.20 increase in ORDs per 100,000 population (95 % CI 0.11-0.30). Early Medicaid expansions were associated with lower PCPV (-2.20, 95 % CI -2.97 to -1.43). CONCLUSIONS: Our findings validate the relationship between PCPV and ORDs, identify important environmental drivers of the opioid epidemic, and suggest early state Medicaid expansions were beneficial in reducing opioid pill volume.