Benefits and risks of increasing restrictions on access to costly drugs in Medicaid.

States are reacting to increased Medicaid drug costs by implementing cost-control policies, such as preferred drug lists (PDLs) and prior authorization. PDLs have risks as well as benefits. Targeting essential drug classes with heterogeneous patient responses and side effects could reduce appropriate care, adversely affect health status, and cause shifts to more costly types of care. Assessing inappropriate use of high-cost drugs before implementing regulations and instituting simple mechanisms to exempt high-risk patients could maximize savings and minimize harm. The current exponential growth in such policies and the limited evidence base justifies investment in research to identify which policies can achieve savings without unintended consequences.