Medicare Part B or Part D: Which Pays for Your Drugs?

Medicare Part D generally covers prescription drugs you fill at a pharmacy. Part B covers drugs you receive in a doctor's office or hospital outpatient setting, such as infusions, some injections, and certain vaccines.

Key takeaways

• Medicare Part D covers most prescription drugs you take at home or fill at a pharmacy.
• Medicare Part B covers drugs given by a medical professional in a clinical setting.
• Insulin coverage depends on how it is administered; most is covered by Part D.
• Certain vaccines are covered by Part B, while others are covered by Part D.
• Review your plan's formulary and benefits carefully, as coverage details can vary.

What Does Part D Cover?

Medicare Part D is your prescription drug coverage. It helps pay for most medications you would pick up at a pharmacy. These are drugs you take yourself, usually at home. This includes a vast array of common prescriptions, from antibiotics to cholesterol-lowering medications.

Every Part D plan has a list of covered drugs, called a formulary. This list includes a wide range of generic and brand-name prescription medications. Formularies categorize drugs into tiers, which directly affect your copayments. For example, a tier 1 drug might have a copay of $5, while a tier 4 drug could cost $100.

Formularies can also include rules like prior authorization or step therapy. Prior authorization means your doctor needs approval from your plan before you can get a certain drug. Step therapy means you must try a less expensive drug first before your plan will cover a more costly one. Always check your plan's specific formulary and its rules.

Most insulin you inject yourself is covered under Part D. This includes insulin pens, vials, and syringes used for self-administration. Part D also covers some vaccines, like the shingles shot, which are not typically covered by Part B, helping protect against various illnesses.

When you enroll in a Part D plan, you will pay a monthly premium. This premium is in addition to your Part B premium. You may also have an annual deductible, copayments, and coinsurance for your prescriptions. These costs are set by your specific plan.

The 2026 maximum Part D deductible is $615. However, many plans offer a lower deductible, or even no deductible at all. After you meet your deductible, your plan begins to pay its share for your drugs, reducing your out-of-pocket spending.

Understanding Part D Drug Costs

Your Part D costs involve several phases throughout the year. After you meet your deductible, you enter the initial coverage phase. During this time, your plan pays a share of your drug costs, and you pay a copayment or coinsurance. For example, if a tier 2 brand-name drug costs $100, your plan might pay $70, and you pay a $30 copay.

Many people used to worry about the "donut hole," also known as the coverage gap. The good news is that the coverage gap has been eliminated. This change, phased in by the Inflation Reduction Act, means you move directly from initial coverage to the catastrophic phase. You can learn more about how this works in our article on understanding your Part D $2,100 drug cap and the eliminated donut hole.

In the catastrophic phase, you pay nothing for covered Part D drugs for the rest of the year. This happens once your out-of-pocket spending reaches a certain limit. For 2026, this annual out-of-pocket cap is $2,100. This cap provides significant financial protection for those with very high drug costs, ensuring predictable maximum spending.

If you face high out-of-pocket drug costs, the Medicare Prescription Payment Plan can help. This plan allows you to spread out-of-pocket drug costs over monthly bills. You pay $0 at the pharmacy counter when you join, for the remaining months of the calendar year. Every Medicare drug plan must offer this option, and there is no cost threshold to qualify. The plan does not lower your total drug costs; instead, it changes when you pay them, making high costs more manageable monthly. Our article on managing high drug costs: the Medicare Prescription Payment Plan has more details on this valuable program.

What Does Part B Cover?

Medicare Part B covers medical services and supplies. This includes certain drugs you receive in a doctor's office or hospital outpatient clinic. These are drugs that a healthcare professional administers to you, not ones you take yourself at home. They must be medically necessary for your diagnosis or treatment.

Examples of Part B-covered drugs include infused medications for chronic conditions. These might be for diseases like multiple sclerosis, Crohn's disease, or rheumatoid arthritis. They also include intravenous immune globulin (IVIG) treatments. Chemotherapy drugs given in an outpatient setting are also typically covered by Part B.

Certain injectable drugs, when administered by a doctor or other medical professional, fall under Part B. These could include some specialty medications for conditions like macular degeneration (eye injections) or osteoporosis (bone-strengthening injections). The key is that they are given in a medical setting by a professional.

Part B also covers insulin used with an insulin pump, as the pump itself is durable medical equipment (DME). The insulin for the pump is part of the DME benefit, ensuring comprehensive coverage for this form of diabetes management. Additionally, certain preventative vaccines, like flu shots, pneumonia shots, and the Hepatitis B shot (for those at medium or high risk), are covered by Part B.

When Part B covers your drugs, you generally pay 20% of the Medicare-approved amount. This is after you have met your annual Part B deductible. The 2026 Part B deductible is $283. For example, if a Part B drug costs $1,000 after your deductible, you would pay $200. This 20% coinsurance applies to the drug itself and the administration services.

Understanding your Part B costs is crucial, as there is no out-of-pocket maximum under Original Medicare for Part B services. However, if you have a Medigap (Medicare Supplement) policy, it may help pay for your Part B coinsurance.

Part B vs. Part D: A Quick Comparison

Understanding the difference between Part B and Part D coverage is important. It ensures you know what to expect for your medication costs. The table below highlights key distinctions between these two parts of Medicare.

This comparison clearly shows that where you get your drug and how it's given determines coverage. This is a common point of confusion for many Medicare beneficiaries. Knowing this distinction can help you better manage your healthcare budget and avoid unexpected bills.

Insulin and Vaccines: Dual Coverage Explained

Insulin coverage can sometimes be confusing due to how it's administered and the device used. Most insulin that you inject yourself, using pens, vials, or syringes, is covered under Part D. This is because it's considered a self-administered prescription drug, typically filled at a pharmacy.

However, if you use an insulin pump (external or implanted), the insulin delivered by the pump is covered under Part B. The reason for this is that the pump is classified as durable medical equipment (DME). Medicare Part B covers DME, and the insulin used with it is considered part of that benefit, emphasizing the medical device aspect.

Vaccines also have split coverage, depending on the type and purpose. Part B covers certain preventative vaccines that are crucial for public health. These include annual flu shots, pneumonia shots (both Pneumococcal conjugate and polysaccharide vaccines), and Hepatitis B shots for people at medium or high risk of infection.

Other important vaccines, such as the shingles vaccine, are typically covered by a Part D plan. Travel vaccines, for example, are generally not covered by either part, though some Part D plans might offer limited coverage. It's always a good idea to check with your specific plan or doctor about coverage for any vaccine you need. This ensures you understand your costs before getting the shot.

What if I Have a Medicare Advantage Plan?

Medicare Advantage Plans (Part C) are an alternative to Original Medicare. These plans are offered by private companies approved by Medicare. They combine your Part A (hospital) and Part B (medical) coverage. Most Medicare Advantage Plans also include prescription drug coverage (MAPD).

If you have an MAPD plan, it will cover both your Part D-type drugs and your Part B-type drugs through the plan. This means your plan sets the rules for deductibles, copayments, and coinsurance for all your medications. While the plan is integrated, the distinction between what would typically be Part B or Part D coverage still applies for how the plan processes claims and determines its share of costs.

Your out-of-pocket costs with an MAPD plan may differ significantly from Original Medicare with a stand-alone Part D plan. It is crucial to review your plan's Evidence of Coverage (EOC) document each year. This document details your specific drug benefits, costs, any limitations, and the plan's formulary.

Always verify that your doctors, specialists, and pharmacies are in your plan's network. Also, check that your specific medications are on the plan's formulary. Even with a Medicare Advantage plan, understanding the Part B and Part D drug categories helps you navigate your benefits and ensures you receive the care and medications you need.

Navigating Your Drug Costs and Coverage

To avoid unexpected costs, it is vital to be proactive about your drug coverage. First, make a comprehensive list of all your prescription drugs. Include dosages, how each is administered (e.g., pill, injection, infusion), and how often you take them. This list is your essential tool for evaluating plans.

Next, contact your current or prospective Medicare plan provider directly. Their contact information is usually on your member ID card or on Medicare.gov. Ask them how each drug on your list is covered. Confirm if it falls under Part B or Part D, and what your estimated costs will be, including any copayments or coinsurance.

Talk to your doctor about how your medications will be administered. For example, if a new drug could be taken orally or given as an infusion, discuss the coverage implications with your doctor. Your doctor or pharmacist can often provide valuable guidance on the most suitable approach for your health and coverage.

During Medicare's Annual Open Enrollment, from October 15 to December 7, carefully compare available plans. Use your personalized drug list to find a plan that effectively addresses your specific medication needs and offers strong value. Plan offerings, formularies, and costs change annually, so what was a good fit last year might not be this year.

If you have limited income and resources, you might qualify for Extra Help (the Low-Income Subsidy). Extra Help assists with Part D plan premiums, deductibles, and copayments. For 2026, for those who qualify, copays are at most $5.10 for a generic and $12.65 for a brand-name drug (lower for some people with Medicaid). This program can make a substantial difference in your out-of-pocket drug costs, making essential medications more affordable. You can learn more about this valuable program in our article, "Extra Help (LIS): Do You Qualify, and Its Value."

Remember that plan details, including covered drugs and costs, vary widely. They depend on your location and the insurance carrier. What one plan covers, another might cover differently, or not at all. Always refer to official Medicare sources like Medicare.gov for the most accurate and up-to-date information on your specific options. For a deeper dive into how Part D plans generally operate, you might find our article "Medicare and Prescriptions: How Part D Drug Plans Work" helpful.

Have questions? Call 1-877-443-3251 to talk it through with a licensed insurance agent. They're paid by the plans they represent, never by you, and the decision stays yours.

We do not offer every plan available in your area. Any information we provide is limited to those plans we do offer in your area. Please contact Medicare.gov or 1-800-MEDICARE to get information on all of your options. Medicare has neither reviewed nor endorsed this information.