Prescription drug cost containment is a key health policy priority. State Medicaid programs have implemented policies requiring prior authorization before paying for angiotensin-receptor blockers (ARBs), a costly class of blood pressure medications. We examined the impact of these policies on drug use. We found that policies using a stepped-therapy approach reduced ARB use by 1.6 percent when first implemented and decreased the subsequent trend in ARB use by 1.3 percent per quarter; alternative approaches were unsuccessful. These findings have important implications for the development of rational drug reimbursement policy under Medicare Part D and other health insurance plans.