The effects of prescription drug copayments on statin adherence

Abstract

BACKGROUND: High copayments may present a barrier to medication adherence among patients with chronic conditions such as hyperlipidemia. OBJECTIVE: To assess the effects of statin copayments on statin adherence among individuals with employer-based insurance. STUDY DESIGN: We used a cross-sectional time-series design, with patient as the cross section and month as the time unit. METHODS: Medical and pharmacy claims among continuously enrolled statin users were selected from the 2000-2003 Medstat MarketScan database. Generalized estimating equation models were used to estimate the effects of copayment changes on statin adherence. Adherence was derived from the medication possession ratio, which represents the percentage of days on therapy each month. Separate estimates were obtained for new statin users (n = 142 341) and for continuing statin users (n = 92 344). RESULTS: Higher copayments were associated with lower statin adherence rates. A 100% index copayment increase had a larger effect on monthly adherence (2.6 and 1.1 percentage point decreases in adherence among new users and continuing users, respectively [both P < .01]) than a 100% copayment increase over time (a 1.1 percentage point decrease among new users [P < .01] and a nonsignificant decrease among continuing users). In all models, new statin users were more price sensitive than continuing users. CONCLUSIONS: High copayments are a financial barrier to statin adherence. The index copayment amount can affect compliance with statin use. Given the relationship between statin use and decreased frequency of cardiovascular events and procedures, the implications of high copayments should be considered by policy makers.