Medicare Part D is also known as the Medicare prescription drug benefit. It  is a federal program to subsidize the costs of prescription drugs and prescription drug insurance premiums for Medicare beneficiaries. It was enacted as part of the Medicare Modernization Act of 2003 and went into effect in 2006.

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. Beneficiaries obtain the Part D drug benefit through two types of plans administered by private insurance companies: the beneficiaries can join a standalone Prescription Drug Plan (PDP) for drug coverage only, or they can join a public Part C health plan that jointly covers hospital and medical services and includes prescription drugs.