From Insurance Lounge

Generally, Original Medicare does not cover prescription drugs. However, Medicare does cover some drugs in certain cases such as immunosuppressive drugs for transplant patients and some oral anti-cancer drugs. Medicare also covers certain prescription drugs used in nebulizers and external infusion pumps.

If you get Medicare covered prescription drugs, make sure your pharmacy or supplier is enrolled in the Medicare Program. If you go to a pharmacy that is not enrolled, Medicare will not pay. You will be responsible for paying the entire bill. Under current law, all Medicare enrolled pharmacies must accept assignment for Medicare covered drugs and biologicals. If you purchase these items from a Medicare-enrolled pharmacy or supplier, you should only pay your 20% co-pay (and any remaining Medicare Part B deductible) when you get your prescription or supplies. Medicare will pay the remaining 80% directly to the pharmacy or supplier after they submit the claim.

Many Medicare Advantage plans cover prescription drugs, up to certain dollar limits (sometimes for an extra cost). Some Medigap policies and states also cover prescription drugs.