Medicare Part D covers most prescription drugs, but not all — and what you pay depends on which plan you choose and which drug you need

Medicare Part D is the prescription drug benefit. It covers thousands of medications, but the exact list changes every year and varies by plan. Part D does not cover all drugs: it excludes certain categories by law, and individual plans can refuse to cover specific medications even within allowed categories. The drugs Part D covers are listed in each plan's formulary — a document you can search online before you join.

What Part D covers breaks into two parts: what the law allows it to cover, and what your specific plan chooses to cover. Understanding both matters, because a drug might be legal for Part D to cover but not covered by your plan.

Key Takeaways

  • Medicare Part D covers most prescription drugs, but each plan publishes its own formulary listing which drugs it will pay for.
  • Part D cannot cover certain categories by law: most over-the-counter drugs, vitamins, cold medicines, and drugs used to treat erectile dysfunction.
  • A drug covered by one Part D plan may not be covered by another, so comparing formularies before you join matters.
  • If your plan refuses to cover a drug your doctor prescribed, you can request an exception, and the plan must respond within 72 hours.
  • Insulin is covered by Part D, but the amount you pay out of pocket is capped at $35 per month for a 30-day supply.

What Part D covers by law

Federal law requires Part D plans to cover drugs in six broad categories: anticonvulsants, antidepressants, antipsychotics, antiretrovirals (for HIV), immunosuppressants, and statins. Beyond those six, plans have flexibility. Most Part D plans cover thousands of additional drugs across nearly every therapeutic class — cancer medications, antibiotics, blood pressure drugs, diabetes medications, and many others.

The drugs that are covered must be prescribed by a doctor. Over-the-counter medications you buy without a prescription are not covered, with rare exceptions. Vitamins, minerals, and nutritional supplements are not covered. Cold and cough medicines, allergy pills, and pain relievers you can buy at a pharmacy counter are not covered. Drugs used to treat erectile dysfunction (like sildenafil or tadalafil) are not covered. Drugs used for weight loss are not covered. Fertility drugs are not covered.

Compounded drugs — medications mixed by a pharmacist to a patient's specific needs — may or may not be covered depending on the plan and whether the compounded version is medically necessary.

How to find out what your plan covers

Each Part D plan publishes a formulary, a list of covered drugs organized by medication name and category. You can search the formulary on the plan's website or call the plan's customer service number. The formulary also tells you which tier the drug falls into — tier 1 drugs cost less out of pocket, tier 4 and 5 drugs cost more. Some drugs require prior authorization, meaning your doctor must get approval from the plan before the pharmacy will fill it. Some drugs have quantity limits, meaning the plan will only pay for a certain amount per month.

If you are thinking about joining a Part D plan, you can compare formularies before you sign up. Medicare's Plan Finder tool lets you search specific drugs and see which plans cover them and at what cost. This is especially important if you take multiple medications or expensive drugs — the same drug can cost very different amounts depending on which plan you choose.

Formularies change every year on January 1. If a drug you take is covered this year, check again in the fall when plans announce their new formularies, because coverage can change.

What happens if your plan does not cover your drug

If your doctor prescribes a drug that your Part D plan does not cover, you have options. You can ask your doctor to prescribe a different drug that the plan does cover — often a generic version or a drug in the same family. You can pay out of pocket for the uncovered drug. Or you can request a coverage exception from your plan.

A coverage exception is a formal request asking the plan to cover a drug it normally would not. Your doctor submits the request, explaining why this specific drug is medically necessary for you. The plan must respond within 72 hours. If the plan says no, you can appeal. Many plans approve exceptions when the doctor provides medical justification, especially if you have already tried other drugs in that category and they did not work.

Insulin and other high-cost drugs

Insulin is covered by all Part D plans. Starting in 2024, your out-of-pocket cost for a 30-day supply of insulin is capped at $35 per month, no matter which insulin you use or how much it costs. This cap applies only to insulin, not to other diabetes drugs.

Other expensive drugs — cancer medications, biologic drugs, and specialty pharmaceuticals — are covered by Part D, but they usually fall into the highest cost tiers. You may pay a percentage of the cost rather than a flat copay. Some plans require prior authorization or step therapy, meaning you must try a cheaper drug first before the plan will cover the expensive one.

Brand-name drugs versus generics

Part D covers both brand-name and generic drugs. Generic drugs are chemically identical to brand-name drugs but cost less. Most Part D plans encourage you to use generics by charging lower copays for them. If your doctor prescribes a brand-name drug and a generic version exists, the plan may cover only the generic unless your doctor requests a brand-name exception.

Some brand-name drugs have no generic equivalent, either because the patent has not expired or because no manufacturer has made a generic version. These drugs are covered if they are on the plan's formulary, but you will pay the brand-name copay or coinsurance.

Drugs covered during the coverage gap

Part D has a coverage gap — a range of drug costs where you pay more out of pocket. In 2024, the gap begins after you and your plan have spent $5,850 together on covered drugs, and it ends when your out-of-pocket spending reaches $8,550. During the gap, you pay 25 percent of the cost of brand-name drugs and generic drugs. Once you reach the $8,550 threshold, catastrophic coverage begins and you pay only a small copay or coinsurance.

Not all drugs are covered the same way during the gap. Insulin is capped at $35 per month even in the gap. Some other drugs may have different cost-sharing rules. Check your plan's summary of benefits to understand what you will pay during each stage.

Frequently Asked Questions

Does Medicare Part D cover my blood pressure medication?

Most blood pressure medications are covered by Part D plans, but not all plans cover all medications in this category. Search your plan's formulary by the drug name to confirm coverage. If your plan does not cover the specific drug your doctor prescribed, ask your doctor about alternatives or request a coverage exception.

Are antibiotics covered by Part D?

Yes, most antibiotics are covered by Part D plans. However, some newer or more expensive antibiotics may require prior authorization or may not be on every plan's formulary. Ask your pharmacist or plan before filling the prescription.

Does Part D cover my thyroid medication?

Thyroid medications like levothyroxine are covered by virtually all Part D plans because they are inexpensive and essential. Generic versions are widely available and usually have low copays.

What if I need a drug that Part D does not cover?

You can pay the full cost out of pocket, ask your doctor to prescribe a covered alternative, or request a coverage exception from your plan. Your doctor can submit the exception request, and the plan must respond within 72 hours. If denied, you can appeal.

Can my Part D plan stop covering a drug I have been taking?

Yes. Formularies change every January 1. If a drug you take is removed from coverage, your plan must notify you in advance. You can request a coverage exception, switch to a different Part D plan during open enrollment, or work with your doctor to find a covered alternative.