Beneficiaries can obtain the Medicare drug benefit through two types of private plans: beneficiaries can join a Prescription Drug Plan (PDP) for drug coverage only or they can join a Medicare Advantage plan (MA) which was discussed above that may cover 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. 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.