Medicare Part D Medication Formulary: What Medications Does Part D Cover?

What is a Medicare Part D formulary?

A Medicare Part D formulary is a plan’s list of covered prescription drugs. Each Medicare drug plan has its own formulary, so a medication covered by one plan may not be covered the same way by another plan.

A formulary can include generic drugs, brand-name drugs, original biological products, and biosimilars. Plans also place covered drugs into cost-sharing levels called tiers. A lower tier usually means a lower cost, while a higher tier may mean a higher copayment or coinsurance.

How do Medicare Part D drug tiers and deductibles work?

Many Medicare Part D plans use five drug tiers, although the exact number of tiers and how each tier is structured can vary by plan. Lower tiers generally include lower-cost generic or preferred drugs, while higher tiers generally include non-preferred and specialty medications.

Many plans apply the deductible differently by tier. Tiers 1 and 2 are often available without first satisfying the plan deductible, while the deductible may apply to drugs in Tiers 3, 4, and 5. This is plan-specific, so check the plan’s Evidence of Coverage and formulary to see how its deductible applies to each tier.

For 2026, the standard Part D deductible is $615, although a plan can charge a lower deductible or no deductible. Once your out-of-pocket spending for covered Part D drugs reaches $2,100 in 2026, you enter catastrophic coverage and pay $0 for covered Part D drugs for the rest of the year. If a drug is not on your plan’s formulary, its cost generally does not count toward the Part D out-of-pocket limit unless the plan approves coverage through an exception. CMS confirms the 2026 Part D deductible and $2,100 out-of-pocket threshold.

What medications does Part D cover?

Part D plans must cover a wide range of prescription drugs commonly used by people with Medicare. In general, Part D is designed to help pay for outpatient prescription drugs you get at a pharmacy or through a plan-approved pharmacy option.

Part D formularies commonly include:

• Generic prescription drugs
• Brand-name prescription drugs
• Many drugs used for chronic conditions, such as diabetes, high blood pressure, heart disease, and mental health conditions
• Some specialty drugs, depending on the plan’s formulary and rules
• Many adult vaccines recommended by the Advisory Committee on Immunization Practices when they are not covered by Part B

Because formularies vary, the most reliable way to know whether a specific medication is covered is to check the plan’s current drug list.

Are some drug categories given special protection?

Yes. Medicare requires Part D plans to include broad coverage for certain categories or classes of drugs. These are often called protected classes because they are used for conditions where interruption in therapy can be especially important.

CMS identifies six protected classes:

• Antidepressants
• Antipsychotics
• Anticonvulsants
• Immunosuppressants for treatment of transplant rejection
• Antiretrovirals
• Antineoplastics

Even within these classes, plan rules can still apply in limited circumstances, so beneficiaries should review the plan formulary and any coverage restrictions.

What drugs are covered by Part B instead of Part D?

Some outpatient drugs are covered under Medicare Part B rather than Part D. Part B generally covers certain drugs under specific conditions, such as drugs you would not usually give to yourself and that are administered in a doctor’s office or hospital outpatient setting.

Examples can include certain injectable or infused drugs, some transplant-related immunosuppressive drugs, and certain vaccines such as flu, pneumococcal, COVID-19, and hepatitis B vaccines when Medicare’s Part B rules apply. If a drug is covered by Part B, it generally is not treated as a standard Part D formulary drug.

What rules can apply to covered Part D drugs?

A drug being on the formulary does not always mean it is covered without conditions. Medicare drug plans may use coverage rules to manage how certain medications are covered.

Common rules include:

• Prior authorization: The plan must approve the drug before it will cover it.
• Step therapy: You may need to try a lower-cost or preferred drug first, unless an exception is approved.
• Quantity limits: The plan may limit how much of a medication it covers at one time or during a set period.
• Network pharmacy rules: Costs and coverage may depend on using a pharmacy that works with your plan.

These rules vary by plan and by medication.

What if your medication is not on the formulary?

If your medication is not on your plan’s formulary, a similar covered drug may be available. If you and your prescriber believe the covered alternatives will not work for your condition, you or your prescriber can ask the plan for a formulary exception.

An exception is a plan decision to cover a drug that is not on its drug list or to waive a coverage rule. Your prescriber usually must provide a medical reason supporting the request. Plans can also have transition fill rules when you first join a plan or when coverage changes, so check your plan documents if you are already taking a medication.

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