Individuals eligible for Medicare can enroll in a standalone Part D plan to complement their Original Medicare (Parts A and B) coverage or choose a Medicare Advantage plan that includes prescription drug coverage (MAPD). These plans have a formulary, which is a list of covered drugs, and each drug on the list is placed in different "tiers" with varying cost-sharing amounts. Beneficiaries typically pay a monthly premium for the Part D plan in addition to any premium for their Medicare Supplement plan.

When a beneficiary needs a prescription, they may pay a copayment or coinsurance, and the plan covers the remaining cost up to a certain limit. Once the beneficiary reaches the plan's out-of-pocket limit, catastrophic coverage begins, and costs are significantly reduced for the remainder of the year. It's important for beneficiaries to understand the formulary, coverage stages, and any cost-sharing obligations associated with their specific Part D plan.