Effect of patient medication cost share on adherence and glycemic control.

PURPOSE To evaluate the effect of patient cost-sharing on oral diabetes medication adherence and glycemic control. DESIGN Retrospective observational study. METHODOLOGY Medical and pharmacy claims from a managed care plan and electronic medical records (EMR) from a large physician organization in Oregon were used to identify a cohort with diabetes. Medication adherence and mean patient cost share was obtained from claims. Glycosylated hemoglobin (A(1c)) values were obtained from an EMR database. PRINCIPAL FINDINGS Lower mean cost share for patients was associated with higher medication adherence. Each $5 increase in patient cost share resulted in a 15 percent decrease in the adjusted odds of being adherent and a 0.1 percentage point increase in A(1c). CONCLUSION Increased medication cost share resulted in a decrease in adherence and poorer glycemic control. Employers and insurers should consider the potential consequences of increased medication cost share on diabetes-related outcomes and health care costs.