Effect of Medicaid Policy Changes on Medication Adherence: Differences by Baseline Adherence

Area of Science:

• Health Services Research
• Health Economics
• Public Health Policy

Background:

• North Carolina (NC) Medicaid implemented prescription supply limits (100 to 34 days) and increased copayments in 2001.
• Previous studies indicated policy changes decreased medication adherence by 2.9-8.0 percentage points in specific populations.
• The heterogeneous effects of these policies based on baseline adherence in the Medicaid population remained unstudied.

Purpose of the Study:

• To investigate the heterogeneous effects of NC Medicaid policy changes on medication adherence across different baseline adherence levels.
• To analyze how prescription day supply restrictions impact adherence in subgroups defined by prior medication-taking behavior.

Main Methods:

• A partial difference-in-difference-in-differences model with fixed effects was employed.
• Medicaid enrollees using long prescriptions (>40 days) were compared to those using short prescriptions (<40 days) and Georgia Medicaid enrollees with a 31-day supply limit.
• Medication adherence was assessed using the proportion of days covered (PDC) and stratified into fully adherent (≥80%), partially adherent (50%-79%), and nonadherent (≤50%) groups.

Main Results:

• Fully adherent enrollees experienced a 2.0 and 1.2 percentage-point decrease in adherence for lipid-lowering drugs and antihypertensives, respectively.
• Nonadherent and partially adherent individuals in the statin group showed an increase in adherence by 1.7-2.6 percentage points.
• These findings highlight differential impacts of policy changes based on baseline adherence levels.

Conclusions:

• Medication adherence responses to cost-containment policies are heterogeneous within the Medicaid population.
• Fully adherent individuals reduced adherence post-policy, whereas partially adherent and nonadherent individuals maintained or improved adherence.
• Managed care strategies should consider enrollees' baseline characteristics for effective cost control and adherence improvement.