Effect of medicaid policy changes on medication adherence: Differences by baseline adherence

BACKGROUND: In 2001, the North Carolina (NC) Medicaid program reduced the number of days prescription supply that enrollees could fill from 100 days to 34 days and increased copayments for brand-name medications. Previous work has shown that a change in these policies led to a decrease in medication adherence from 2.9 to 8.0 percentage points in specific populations with chronic conditions. Studies have also shown that days supply limits and copayment increases have heterogeneous effects based on enrollees' baseline characteristics, including baseline adherence. However, this phenomenon has not been studied in the Medicaid population. We undertook this study to assess the heterogeneous effect of the NC Medicaid policy changes in groups with varying levels of baseline adherence. OBJECTIVE: To examine whether restrictions on days supply had heterogeneous effects in subgroups defined by medication adherence before the policy changes. METHODS: A partial difference-in-difference-in-differences model with fixed effects was used to compare medication adherence before and after the NC Medicaid policy changes among Medicaid enrollees subject to the policy changes because of their use of long prescriptions (> 40 days) as compared with (a) NC Medicaid enrollees using short prescriptions (< 40 days) before policy adoption, as well as (b) Medicaid enrollees in Georgia restricted to a 31 days supply through the study period. Medicaid enrollees were included if they filled a prescription for 1 of the following medication classes: antihypertensives, lipid-lowering drugs, or antipsychotics. The effect of the policy changes on medication adherence, calculated using the proportion of days covered (PDC) each quarter by baseline adherence level and clinical condition group, was studied. Average adherence levels over the 18-month prechange period were used to stratify individuals into 3 baseline adherence groups: fully adherent (PDC ≥ 80%), partially adherent (50%-79%), and nonadherent (PDC ≤ 50%). RESULTS: Enrollees fully adherent at baseline observed a 2.0 (P = 0.001) and 1.2 (P < 0.001) percentage-point decline in adherence for the lipidlowering drug and antihypertensive cohorts, respectively, in the period after the policy changes. The nonadherent and partially adherent cohorts in the statin group observed an increase in adherence by 1.7-2.6 (P < 0.05) percentage points in the post-index period. CONCLUSIONS: Adherence changes after cost containment policies have a heterogeneous effect on individuals with varying baseline adherence in the Medicaid population. Individuals fully adherent at baseline decreased adherence following policy changes, while individuals partially adherent and nonadherent at baseline either had no change or showed increases in adherence, possibly because of increased contact with pharmacists and clinicians required by shorter prescription lengths. Managed care strategies to control costs should take into consideration the heterogeneity of responses by the enrollees to these policies. Furthermore, policies that consider baseline characteristics of enrollees may be more effective in improving adherence.