Do open formularies increase access to clinically useful drugs?

Before 1990 many state Medicaid programs maintained "restrictive" formularies, which denied reimbursement for unlisted prescription drugs. This type of formulary has been criticized for denying important medications to poor, medically needy persons. As part of the Omnibus Budget Reconciliation Act of 1990, restrictive formularies in Medicaid programs were disallowed. Based on research into the 200 top-selling prescription drugs in the United States, we conclude that eliminating Medicaid restrictive formularies improved access to a subset of the 200 best sellers, but that the majority of these products offered only questionable or no additional therapeutic benefit.