Drugs covered under Medicare Formularies can differ from plan to plan. However, plans must cover at least two prescription drugs within defined categories and almost all antidepressants, antipsychotics, immunosuppressants, anticonvulsants, HIV/AIDS drugs and cancer drugs, explains Medicare.gov.
All Medicare Formularies must cover medically necessary drugs, which are defined as supplies or services essential for diagnosing and treating an insured person’s condition and that follow accepted criteria. Both brand name and generic drugs are covered by Medicare plans. Often, Medicare plans break up formularies into tiers to distinguish by cost. Generic drugs fall under Tier 1 in most plans and cost the least to an insured person. Preferred brand-name drugs are housed under Tier 2 and cost more than Tier 1 drugs but less than Tier 3 drugs, which are non-preferred brand-name drugs. Although not usually required, plans often also cover drugs for weight gain and loss and drugs for erectile dysfunction.
A Medicare plan may change its formulary during the year. If an insured person’s drug is affected by said change, the provider must either notify that person 60 days in advance of the change or provide written notice at the time of the refill in addition to a 60-day supply of the drug under the rules of the plan prior to the change.
Some plans require approval before a certain drug can be prescribed, meaning that the insured person's doctor must prove to the plan provider that the drug is medically necessary to treat that person's condition.