The role of health insurance on treatment for opioid use disorders: Evidence from the Affordable Care Act Medicaid expansion.

We estimate the effect of health insurance coverage on opioid use disorder treatment utilization and availability by exploiting cross-state variation in effective dates of Medicaid expansions under the Affordable Care Act. Using a difference-in-differences design, we find that aggregate opioid admissions to specialty treatment facilities increased 18% in expansion states, most of which involved outpatient medication-assisted treatment (MAT). Opioid admissions from Medicaid beneficiaries increased 113% without crowding out admissions from individuals with other health insurance. These effects appeared to be driven by market entry of select MAT providers and by greater acceptance of Medicaid payments among existing MAT providers. Moreover, effects were largest in expansion states with comprehensive MAT coverage. Our findings suggest that Medicaid expansions resulted in substantial utilization and availability gains to clinically efficacious and cost-effective pharmacological treatments, implying potential benefits of expanding Medicaid to non-expansion states and extending MAT coverage.