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.
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.
A drug in a lower tier will generally cost you less than a drug in a higher tier. In some cases, if your drug is on a higher tier and your prescriber thinks you need that drug instead of a similar drug on a lower tier, you or your prescriber can ask your plan for an exception to get a lower copayment.