Role of Subsidized Coverage Eligibility in Medication Adherence Among Patients With Hypertension and Diabetes: Evidence From the NHIS 2011–2018

Introduction: The subsidized insurance provision under the Affordable Care Act is an important instrument for health insurance coverage among middle-income nonelderly individuals. However, unlike the health impacts of the Medicaid expansion under the Affordable Care Act, the impact of subsidized insurance is relatively less explored in extant literature. This study aims to assess the role of subsidized coverage eligibility in medication adherence among nonelderly patients with hypertension and diabetes in the U.S. Methods: Using pooled data from 8 rounds (2011–2018) of the National Health Interview Survey, we estimated a difference-in-differences model to examine the change in medication adherence among study participants with a household income of 150%–399% of the Federal Poverty Line compared with that among their counterparts with a household income of ≥400% of the Federal Poverty Line during pre‒ and post‒Affordable Care Act periods. We also performed event study analysis and falsification tests to check the validity of our quasi-experimental design. Analyses were conducted in 2022. Results: Medication adherence in the treatment group increased by 4.5 percentage points (95% CI=2.8, 6.2) during the post‒Affordable Care Act periods, whereas the increase was only 1.8 percentage points (95% CI=0.6, 3.0) in the control group. Results of the difference-in-differences model suggest that because of the subsidized insurance under the Affordable Care Act, medication adherence in the treatment group increased by 3.1 percentage points (95% CI=1.0, 5.2) during the post‒Affordable Care Act periods, compared with that in the control group. This increase was attributable to the improved insurance coverage, which increased by 6.8 percentage points (95% CI=5.3, 8.4) in the treatment during the post‒Affordable Care Act periods. Conclusions: Our analyses generate evidence that middle-income individuals with hypertensive or diabetic conditions, who were eligible for the subsidized coverage, benefited from this provision of the Affordable Care Act.