Medicare
Prescription Drug Coverage (Part D):
There are Two Ways to Get Medicare Drug Coverage:

Medicare Drug Plans
(Part D)
Medicare Part D Prescription Drug plans add drug coverage to Original Medicare, some Medicare Cost Plans, some Private Fee-for-Service plans, and Medical Savings Account plans.
You must have Medicare Part A (Hospital Insurance) and/or Medicare Part B (Medical Insurance) to join a separate Medicare drug plan.
Medicare Advantage Plan (Part C)
Your other option for Drug coverage is to get all of your Part A, Part B, and Part D Drug coverage, through a Medicare Advantage plan that includes Prescription Drug Coverage.
Remember, you must have Part A and Part B to join a Medicare Advantage Plan, and not all of these plans offer drug coverage.