 The final bill was enacted as part of the Medicare Modernization Act of 2003 (which also made changes to the public Part C Medicare health plan program) and went into effect on January 1, 2006.The various proposals were substantially alike in that Part D was optional, it was separated from the other three Parts of Medicare in most proposals, and it used private pharmacy benefit managers on a regional basis to negotiate drug prices.The differences included one-size-fits-all benefits nationwide in the Clinton/Democrat proposals (as opposed to multiple choices in the Republican plans and the bill finally enacted) and a wide array of deductibles and co-pays (including the infamous "donut hole"); only Bush's initial plan included true catastrophic coverage for middle income seniors, but it was not included and is a feature still not available in Part D.

Individuals on Medicare are eligible for prescription drug coverage under a Part D plan if they are signed up for benefits under Medicare Part A and/or Part B.