A large value-based insurance design program offered by Blue Cross Blue Shield of North Carolina eliminated generic medication copayments and reduced copayments for brand-name medications. Our study showed that the program improved adherence to medications for diabetes, hypertension, hyperlipidemia, and congestive heart failure. We found that adherence improved for enrollees, ranging from a gain of 3.8 percentage points for patients with diabetes to 1.5 percentage points for those taking calcium-channel blockers, when compared to others whose employers did not offer a similar program. An examination of longer-term adherence and trends in health care spending is still needed to provide a compelling evidence base for value-based insurance design.