What Does Medicare Part D Cover?

To take full advantage of your Medicare Part D plan, you need to understand what it does and does not cover. Each plan will have unique features but all Part D plans run on the same fundamental principles.

Learn how Part D plans decide what medications to offer. With this information in hand, you will be able to choose the plan that best meets your needs.

Medications covered by medicare part d
Illustration by Brianna Gilmartin, Verywell 

Part D Formulary

Any insurance plan that offers prescription drug coverage will have a formulary. A formulary is a list of preferred medications that the plan will cover.

The insurance company that offers your Part D plan and the pharmaceutical companies that make the drugs negotiate a deal. Together they decide which medications will be put on that plan’s formulary. Your formulary will not cover every possible medication but it will cover a lot.

Part D plans are required to offer two medications from 148 different drug classes.

For example, there are many classes of medications to treat hypertension: angiotensin converting enzyme (ACE) inhibitors, angiotensin II receptor blockers, beta-blockers, calcium channel blockers, and more. There will be at least two of each of these medications on your plan’s formulary to meet Medicare’s standard benefit.

There are six protected drug classes that all Part D plans must cover:

  • Anticonvulsants (drugs used to prevent seizures)
  • Antidepressants
  • Antipsychotics
  • Cancer drugs
  • HIV/AIDS drugs
  • Immunosuppressants (drugs used to protect transplanted organs)

Most, if not all, of the medications in these categories will be included on every Part D formulary. Medicare requires inclusion of these drugs. Failure to provide one of these critical medications could lead to serious health complications and possibly death.

Understanding Changes

Do not assume that your Part D formulary will stay the same year round. Medications could be added or removed from the formulary at any time. If this affects your medications, your plan will notify you within 60 days. You and your healthcare provider will need to decide whether to change medications or to appeal to your plan to continue the medication.

You will not be allowed to change Part D plans until the Medicare Open Enrollment, which takes place between October 15 and December 7 every year.

An alternative is to take advantage of the Medicare Advantage Open Enrollment Period that runs from January 1 through March 31. If you have a Medicare Advantage plan, you can change to Original Medicare and pick a Part D plan, add a Part D plan to your stand-alone Medicare Advantage plan, or change to a different Medicare Advantage plan with drug coverage.

Generic vs. Brand Name Medications

Your Part D plan formulary will include both generic and brand-name drugs. While some people believe that brand-name medications are better than generics, this is not necessarily true. Generic medications are the same as their brand-name counterparts. They are the same active ingredient and they come in the same doses. The primary difference is who makes the product.

A pharmaceutical company holds the exclusive rights to a medication until its patent expires. United States drug patents last for 20 years. This includes the time the drug was investigated in clinical trials. Clinical trials may last from 6 to 11 years before the drug is reviewed by the Food and Drug Administration (FDA). The FDA approval process may take another 6 to 10 months. By the time a drug hits the market, it is usually 6 to 11 years into its patent.

After the patent expires, other pharmaceutical companies can make the drug as well. Costs drop considerably with competition in the marketplace. Generic drugs can cost as much as 85% less than their brand-name counterparts in some cases.

Do not be surprised when your Part D plan recommends generic in favor of brand-name medications. The intent is to save both you and the insurance company money.

When Brand Name Drugs Are Medically Necessary

Medicare only covers medications it considers to be medically necessary. This requires that you have a medical condition that requires treatment and that the drug in question has been shown to benefit that condition. Generic medications may meet that need but sometimes a brand-name medication is necessary, even if it costs more.

Some brand name medications will not have generic versions available—at least not until their patents expire. In this case, your Part D plan may first recommend that you try another medication in the same drug class, usually a generic, to save money. They may even recommend another class of medication that has generic options, if it could be more cost effective.

There will be times, however, when generic medications will not meet your medical needs:

  • A generic drug is not available in the drug class recommended by your healthcare provider.
  • You did not respond to generic medications in the same drug class.
  • You had side effects to generic medications in the same drug class.
  • You did not respond to generic medications in other drug classes and no other drug classes are available.
  • You had side effects to generic medications in other drug classes and no other drug classes are available.

You will pay more for a brand-name medication than a generic one but your health is what is most important. Your healthcare provider may recommend a brand-name medication based on your health situation. Whenever possible, he or she will choose a drug that is on your formulary.

Medications Excluded

Medicare Part D plans are not all-inclusive. In fact, Medicare will exclude certain medications from coverage. A lot of these are based on medical necessity and include:

  • Barbiturates if not used for specific medical indications
  • Cough and cold medications
  • Drugs used for cosmetic reasons, including drugs for hair growth or weight control
  • Erectile or sexual dysfunction drugs
  • Fertility drugs
  • Over-the-counter medications
  • Prescription vitamins and minerals with the exception of fluoride, niacin, prenatal vitamins and Vitamin D derivatives used for specific medical indications

Part D plans can offer any or all of these medications on their formularies as a supplemental benefit. While you could pay more in premiums, you could have access to medications you would otherwise have to pay out of pocket. You will have to decide if it is worth the added cost.

Keep in mind Medicare Part D does not pay for medical marijuana beyond three FDA-approved cannabinoid medications. These are only covered for very specific medical conditions. This is because the DEA still classifies marijuana as a Schedule I drug.

Finally, Medicare Part D does not allow you to use manufacturer drug coupons to keep prescription drug costs down, even if a medication is covered by your plan. You have to decide to use your Part D coverage or a drug coupon, but not both.


Technically, you could go to any pharmacy to fill your prescriptions, but that could cost you more. Part D plans negotiate with both local and mail order pharmacies to establish a network of preferred pharmacies. The federal government requires that Part D plans include both types of pharmacies in their networks.

You will pay a lower price for your medications if you use one of these preferred pharmacies.

You will need to decide whether to use a local pharmacy or a mail order pharmacy. It is possible you may use both. Some people prefer a local pharmacy because it offers direct access to a pharmacist to answer their questions. A local pharmacy may also be a good option for medications you need to fill immediately, medications that are unlikely to be refilled, or medications that are being titrated, i.e. the dose is being gradually adjusted until the desired effect is achieved.

A mail order pharmacy often sends 90-day supplies of your prescriptions at one time, decreasing your need to travel to a brick and mortar store to get your medications. While this is convenient, there could be issues if your packages arrive late or if your medication doses are changed.

Whether you prefer local or mail order, you will want to choose a preferred pharmacy. When you sign up for a Part D plan, do not assume that a pharmacy you have always used is in their network. Check with your Part D plan or call the pharmacy to find out. Not doing so could cause you to pay more than necessary for your medications. 

Frequently Asked Questions

  • How do you enroll in Medicare Part D?

    You can enroll through the insurance company's website or by mailing them an enrollment form. You can also enroll through Medicare's website or by calling 1-800-MEDICARE (1-800-633-4227). There are certain times you can enroll without a late penalty, including your seven-month Initial Enrollment period, Open Enrollment between October 15 and December 7, and the seven-month period around your 25th month of disability.

  • How much does Medicare Part D cost?

    Most of the time, you'll only pay the Part D premium, which can vary by plan. However, if you don't sign up when first eligible, you may also have to pay a monthly late enrollment penalty. In addition, you might pay more if you have a higher income that's more than $87,000 filing individually or more than $174,000 married filing jointly.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. U.S. Centers for Medicare & Medicaid Services. Your Guide to Medicare Prescription Drug Coverage.

  2. U.S. Food & Drug Administration. Generic Drugs: Questions & Answers.

  3. U.S. Centers for Medicare & Medicaid Services. Medicare Drug Coverage under Medicare Part A, Part B, Part C, & Part D.

  4. Centers for Medicare & Medicaid Services. Your guide to Medicare prescription drug coverage.

  5. Medicare.gov. Monthly premium for drug plans.

By Tanya Feke, MD
Tanya Feke, MD, is a board-certified family physician, patient advocate and best-selling author of "Medicare Essentials: A Physician Insider Explains the Fine Print."