Medicare Part D, also called the Medicare prescription drug benefit, is an optional United States federal-government program to help Medicare beneficiaries pay for self-administered prescription drugs through prescription drug insurance premiums (the cost of almost all professionally administered prescriptions is covered under optional Part B of United States Medicare). Part D was originally proposed by President George W. Bush in 2003 and enacted as part of the Medicare Modernization Act of 2003 and went into effect on January 1, 2006.