The presence of prior-effects of the Medicaid expansion on drug prescription.

BACKGROUND

This study examines whether states implementing the 2014 ACA Medicaid expansion experienced prior changes in physician Medicare Part D prescribing patterns compared with non-expansion states, evaluating potential anticipatory behavioral adaptations.

RESEARCH DESIGN AND

METHODS

Utilizing provider-year panel data from ProPublica's Medicare Part D Prescriber dataset (2011-2016), we implement an event-study difference-in-differences framework across a geographically restricted sample of adjacent expansion/non-expansion border counties. Key physician-level outcomes include total drug costs, low-income subsidy (LIS) claims, non-LIS claims, beneficiary age structures, and brand-name shares.

RESULTS

In preferred border-county models, expansion-state physicians exhibited significantly higher pre-implementation baselines relative to 2013 for log total cost (2011: 3.334, 95% CI [1.441, 5.227], p < 0.01; 2012: 2.923, 95% CI [1.714, 4.132], p < 0.01) and log non-LIS claims, showing a narrowing pre-reform gap. Conversely, LIS claims rose significantly only post-implementation in 2015 (2.112, 95% CI [0.413, 3.811], p < 0.05) and 2016 (3.000, 95% CI [0.738, 5.262], p < 0.01).

CONCLUSIONS

Medicaid policy shifts alter clinician expectations and prescribing behavior prior to formal execution. However, evaluations must be qualified by the data's reliance on Medicare Part D files rather than total historical payer mixes.