Medicare Part D
Individuals are eligible for prescription drug coverage under a Part D plan if they are entitled to benefits under Medicare Part A and/r enrolled in Part B. Beneficiaries can obtain the part D drug benefit through two types of private plans: they can join a Prescription Drug Plan (PDP) for drug coverage only or they can join a Medicare Advantage Plan (MA) that covers both medical services and prescription drugs (MA-PD).
The latter type of plan is actually part of Medicare Part C and has several other differences relative to original Medicare. About two-thirds of Part D beneficiaries are enrolled in a PDP option.
Not all drugs will be covered at the same level, giving participants incentives to choose certain drugs over others. This is often implemented via a system of tiered formularies in which lower-cost drugs are assigned to lower tiers and thus are easier to prescribe or cheaper. 