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Prescription drug formulary

This page covers some helpful questions about Medicare prescription drug formularies. Expand each question below to read the answers.

A formulary is a list of prescription drugs covered by a plan.

Because Medicare Part D is provided by private insurance companies such as Aetna and SilverScript, each company can decide which drugs to cover. However, a formulary must meet the minimum standards and requirements of Medicare Part D coverage.

Medicare Part D formularies are approved by Medicare and updated throughout the plan year, and may change if:


  • The plan no longer covers a drug
  • A new drug is added
  • A drug is moved to a different cost-sharing tier
  • A prior authorization, step therapy restriction or quantity limit has been added or changed for a drug
  • A drug is removed from the market

Plans will let members know about any changes that may affect a drug they take.

Formularies are set up in tiers. A drug in a lower tier usually costs less than a drug in a higher tier. Use a plan’s formulary to tell you which drugs are covered and which tier they are in. The tiers are numbered and include:

Tier 1, Preferred Generic: These are commonly prescribed generic drugs.

Tier 2, Generic: These drugs are generic but usually cost more than the drugs in Tier 1.

Tier 3, Preferred Brand: These are brand-name drugs that don’t have generic versions. They are the lowest-cost brand-name drugs on the list. 

Tier 4, Non-Preferred Drug: These are higher-priced brand-name and generic drugs, less commonly prescribed than drugs in the preferred tiers.

Tier 5, Specialty: These are the most expensive drugs on the list. They may require special handling and/or close monitoring.

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Federal law prohibits a Part D plan from covering certain types of drugs, including:

  • Over-the-counter drugs (also called nonprescription drugs)
  • Drugs when used for treatment of anorexia, weight loss or weight gain
  • Drugs when used for cosmetic or hair growth purposes
  • Drugs when used for the relief of cough or cold symptoms
  • Prescription vitamins and minerals (some exceptions for drugs like fluoride preparations)
  • Drugs when used for the treatment of sexual or erectile dysfunction (ED)

In addition, Medicare Part D plans are unable to cover the following:

  • Drugs that would be covered under Medicare Part A or Part B
  • Drugs not approved by the U.S. Food and Drug Administration (FDA) or that are purchased outside the United States and its territories
  • Off-label use, in many cases, in which a drug is used in any way other than those indicated on a drug's label as approved by the Food and Drug Administration

For more information on formularies, drug tiers and prescriptions, please visit our Unpacking Medicare prescription drug coverage page.

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