The effects of health plan copayments on adherence to oral diabetes medication and health resource utilization.

Objective: To assess the effects of copayments on oral diabetes medication adherence, health resource utilization, and expenditure.

Methods: Retrospective, observational analysis of medical and pharmacy claims data from PPG Industries employees, retirees, and dependents (2003-2005). Average monthly copayments were stratified low (US$0-9), medium (US$10-19), or high (US$20+).

Results: In 2052 individuals, adherence to oral diabetes medication was highest for the low copayment group for both age groups >or=65 years; 84% low, 77% medium, 64% high (P < 0.0001) and <65 years; 74% low, 71% medium, 55% high (P < 0.0001). For patients <65 years, total health care expenditure was 22% lower in the low versus high copayment group (P = 0.024), resulting in average savings of US $3116 per patient per year. Risk of hospitalization was significantly lower in the low versus the high copayment group for patients >or=65 years of age.

Conclusions: High copayments were associated with lower adherence to oral diabetes medications for all patients and higher total health care costs for patients less than 65.