Impact of a prescription copayment increase on lipid-lowering medication adherence in veterans.

BACKGROUND In February 2002, the Department of Veterans Affairs (VA) increased copayments from $2 to $7 per 30-day drug supply of each medication for many veterans. We examined the impact of the copayment increase on lipid-lowering medication adherence. METHODS AND RESULTS This quasiexperimental study used electronic records of 5604 veterans receiving care at the Philadelphia VA Medical Center from November 1999 to April 2004. The all copayment group included veterans subject to copayments for all drugs with no annual cap. Veterans subject to copayments for drugs only if indicated for a non-service-connected condition with an annual cap of $840 for out-of-pocket costs made up the some copayment group. Veterans who remained copayment exempt formed a natural control group (no copayment group). Patients were identified as adherent if the proportion of days covered with lipid-lowering medications was > or =80%. Patients were identified as having a continuous gap if they had at least 1 continuous episode with no lipid-lowering medications for > or =90 days. A difference-in-difference approach compared changes in lipid-lowering medication adherence during the 24 months before and after copayment increase among veterans subject to the copayment change with those who were not. Adherence declined in all 3 groups after the copayment increase. However, the percentage of patients who were adherent (proportion of days covered > or =80%) declined significantly more in the all copayment (-19.2%) and some copayment (-19.3%) groups relative to the exempt group (-11.9%). The incidence of a continuous gap increased significantly at twice the rate in both copayment groups (all copayment group, 24.6%; some copayment group, 24.1%) as the exempt group (11.7%). Compared with the exempt group, the odds of having a continuous gap in the after relative to the before period were significantly higher in both the all copayment group (odds ratio, 3.04; 95% confidence interval, 2.29 to 4.03) and the some copayment group (odds ratio, 1.85; 95% confidence interval, 1.43 to 2.40). Similar results were seen in subgroups of patients at high risk for coronary heart disease, high medication users, and elderly veterans. CONCLUSIONS The copayment increase adversely affected lipid-lowering medication adherence among veterans, including those at high coronary heart disease risk.