Medicare Part B vs. Part D: which covers your drug?

Updated 2026-10-22 · Reviewed for accuracy by the EKO Labs team. Educational only; not medical advice.

If you have Medicare, a prescription drug can be covered in one of two places: Part B (Medical Insurance) or Part D (Medicare drug coverage). Which one pays depends on the drug and on how and where you get it. This guide follows Medicare.gov to explain the difference, what you pay under each, and what to ask when a bill or a pharmacy claim does not look right. It is general information, not legal, financial or medical advice.

The short version

• Part B covers a limited number of outpatient drugs under certain conditions. Usually it covers drugs you would not typically give to yourself, like those you get at a doctor’s office or in a hospital outpatient setting.
• Part D covers many drugs that Part B does not. It is optional, and it is offered by private insurance companies approved by Medicare. If you have Original Medicare, you join a separate Medicare drug plan to get it.

What Part B covers

Medicare.gov lists these examples of Part B-covered outpatient drugs (conditions apply to each):

• Most injectable and infused drugs when a licensed medical provider gives them.
• Drugs used with some durable medical equipment (DME), like an infusion pump, if the drug is medically necessary.
• Some antigen allergy tests and treatments, HIV prevention drugs, and injectable osteoporosis drugs.
• Erythropoiesis-stimulating agents (for example erythropoietin by injection for End-Stage Renal Disease or certain types of anemia), blood clotting factors for hemophilia, and oral End-Stage Renal Disease drugs.
• Intravenous Immune Globulin (IVIG) at home, if you have a diagnosed primary immune deficiency disease and your provider decides it is medically appropriate.
• Flu, pneumococcal and COVID-19 vaccines, and some other vaccines when they are directly related to treating an injury or illness.
• Immunosuppressive drugs, if Medicare helped pay for your organ transplant (you must have Part A at the time of the transplant and Part B when you get the drugs).
• Some oral cancer drugs (when the same drug is available in injectable form, or it is a prodrug of the injectable drug) and some oral anti-nausea drugs used with cancer chemotherapy.

What Part D covers

Part D helps pay for the brand-name and generic drugs you need, including many drugs that Part B does not cover. Each plan has its own drug list (also called a formulary), so check the plan’s list to see which outpatient drugs it covers and at what cost. Part D also generally covers all adult vaccines that the Advisory Committee on Immunization Practices (ACIP) recommends, such as vaccines for RSV, shingles and whooping cough, and your drug plan will not charge a copayment or deductible for them. To learn how plans choose their drugs, see our formulary guide.

You have two options for Part D: a separate Medicare drug plan that adds drug coverage to Original Medicare, or a Medicare Advantage Plan (or other Medicare health plan) that bundles Part A, Part B and usually Part D. If you join a Medicare Advantage Plan that does not offer drug coverage, in most cases you will not be able to add a separate Medicare drug plan.

What you pay under each

Part B drugs

• In most cases, after you meet the Part B deductible, you pay up to 20% of the Medicare-approved amount.
• Doctors, other health care providers and pharmacies must accept assignment for Part B-covered drugs, so they should never ask you to pay more than the coinsurance or copayment for the Part B-covered drug itself.
• Your coinsurance can sometimes be lower for certain Part B drugs whose prices have gone up faster than inflation. The specific drugs and potential savings change every quarter.
• If a Part B drug is part of your hospital outpatient services, you pay a copayment for the services. If you get a drug that is not covered in a hospital outpatient setting, you pay all costs for it unless you have other drug coverage, and what you pay then depends on whether your drug plan covers it and whether the hospital is in the plan’s network.
• You pay nothing (and the Part B deductible does not apply) for COVID-19, flu, pneumococcal and hepatitis B vaccines if your provider accepts assignment.

Part D drugs

• Costs depend on the plan: a monthly premium, an optional deductible, and copayments or coinsurance at the pharmacy. No Medicare drug plan may have a deductible of more than $615 in 2026 ($700 in 2027).
• Generally there are three stages. After any deductible, you pay 25% coinsurance for covered generic and brand-name drugs until your out-of-pocket spending on covered Part D drugs reaches $2,100 in 2026 ($2,400 in 2027). After that you pay nothing for covered Part D drugs for the rest of the calendar year.
• Programs such as Extra Help, Medicaid and the Medicare Prescription Payment Plan can lower or spread your drug costs. See our guides on Extra Help and the Medicare Prescription Payment Plan.

Why the same drug can be billed differently

Because the dividing line is mostly about who gives you the drug and where, the same medicine can fall under different parts. A drug a provider injects in the office is generally a Part B matter, while a drug you pick up at the pharmacy and take yourself is generally a Part D matter. Whether a specific drug is covered at all depends on the drug, your plan and your situation, so Medicare.gov advises checking with your plan and your provider rather than assuming.

Questions to ask

• Is this drug billed to Part B or Part D, and why?
• Is this drug on my plan’s formulary, and does it need prior authorization or have quantity limits? See our prior authorization guide.
• If I get this drug in a hospital outpatient setting, what will I pay for the drug and for the services?
• Does my provider accept assignment?
• Do I need a separate drug plan, or does my Medicare Advantage Plan already include Part D? See Original Medicare vs. Medicare Advantage.

Where to get free help

Call 1-800-MEDICARE (1-800-633-4227, TTY 1-877-486-2048) or contact your State Health Insurance Assistance Program (SHIP), which gives free, local health insurance counseling to people with Medicare and their families. To compare drug plans, see our plan comparison guide.

Sources: Medicare.gov, “Prescription drugs (outpatient)”; “What’s Medicare drug coverage (Part D)?”; “Drug coverage basics”; “How much does Medicare drug coverage cost?” Checked October 2026. Amounts change each year, so confirm current figures on Medicare.gov. This guide is general information, not legal, financial or medical advice.