http://www.cms.hhs.gov/MedicaidDrugRebateProgram/01_Overview.asp
Centers for Medicare and Medicaid Services
The Medicaid Drug Rebate Program requires a drug manufacturer to enter into and have a national rebate agreement with the Secretary of the Department of Health and Human Services for States to receive federal funding for outpatient drugs dispensed to Medicaid patients. Approximately 500 pharmaceutical companies participate in this program. All 50 States and the District of Columbia cover drugs under the Medicaid program.