Does the association between prescription copayment increases and medication adherence differ by race?

Previous studies have shown prescription copayment increases are associated with decreases in adherence to diabetes and hypertension medications, but have not investigated whether these associations differ by race. Veterans Affairs (VA) administrative data were used to analyze medication adherence before and after an increase in prescription copayments from $2 to $7 for a 30-day supply in February 2002. Applying a difference-in-difference approach, we compared adherence changes among White and Black veterans who were exempt from or required to pay medication copayments. The likelihood patients were adherent to diabetes or hypertension medications decreased after the copayment increase for both White and Black veterans. However, differences in medication adherence reductions between White and Black veterans were small and statistically insignificant. Despite barriers faced by minority patients related to lower perceived value of medications, the impact of a copayment increase on adherence was similar across the two largest racial groups in the VA.