Medicare Part D covers a wide variety of prescription medications used by Medicare recipients, including the majority of drugs in those "safe groups," such as cancer or HIV/AIDS drugs. Since each plan has its own formulary, details about a plan's list of covered medications (called a "formulary") is not included in this handbook. On their formularies, several Medicare insurance programs and Medicare health plans that provide drug coverage divide medications into tiers. The cost of drugs in each tier varies. A medicine in a lower tier, for example, would cost you less than a drug in a higher tier.