Increasing time costs and copayments for prescription drugs: an analysis of policy changes in a complex environment.

Objective: To estimate the effect of two separate policy changes in the North Carolina Medicaid program: (1) reduced prescription lengths from 100 to 34 days' supply, and (2) increased copayments for brand name medications.

Data Sources/study Setting: Medicaid claims data were obtained from the Centers for Medicare and Medicaid Services for January 1, 2000-December 31, 2002.

Study Design: We used a pre-post controlled partial difference-in-difference-in-differences design to examine the effect of the policy change on adults in North Carolina; adult Medicaid recipients from Georgia served as controls.