Medicare offers prescription drug coverage to everyone with Medicare. If you decide not to join a Medicare Prescription Drug Plan when you're first eligible, and you don't have other creditable prescription drug coverage, or you don't get Extra Help, you'll likely pay a late enrollment penalty. To get Medicare drug coverage, you must join a plan run by an insurance company or other private company approved by Medicare. Each plan can vary in cost and drugs covered.
Medicare Prescription Drug Plan (Part D). These plans (sometimes called "PDPs") add drug coverage to Original Medicare, some Medicare Cost Plans, some Medicare Private Fee-for-Service (PFFS) Plans, and Medicare Medical Savings Account (MSA) Plans.
Medicare Advantage Plan (Part C) (like an HMO or PPO) or other Medicare health plan that offers Medicare prescription drug coverage. You get all of your Medicare Part A (Hospital Insurance) and Medicare Part B (Medical Insurance) coverage, and prescription drug coverage (Part D), through these plans. Medicare Advantage Plans with prescription drug coverage are sometimes called “MA-PDs.” You must have Part A and Part B to join a Medicare Advantage Plan.
Each Medicare Prescription Drug Plan has its own list of covered drugs (called a formulary). Many Medicare drug plans place drugs into different "tiers" on their formularies. Drugs in each tier have a different cost.