Medicare Part D covers most prescription drugs, but not all — and what your plan pays for depends on which plan you chose and which drug you need

Medicare Part D is prescription drug coverage run by private insurance companies under contract with Medicare. Each plan maintains its own formulary, which is the official list of drugs the plan covers. A drug covered by one Part D plan may not be covered by another, even though both are Medicare plans. Before you fill a prescription, you need to know whether your specific plan covers that specific drug — and what you will pay.

The drugs Medicare Part D does not cover are set by federal law and are the same across all plans. These include most over-the-counter medications, drugs used only in a hospital or doctor's office, most vitamins and minerals, and drugs prescribed for weight loss. Benzodiazepines (like diazepam) and barbiturates have restrictions that vary by plan. If your doctor prescribes a drug that Part D does not cover, you pay the full cost yourself, though your doctor may be able to prescribe a similar drug that is covered.

Key Takeaways

  • Each Part D plan has its own formulary listing which drugs it covers, so the same medication may be covered under one plan but not another.
  • You can search your plan's formulary on Medicare.gov or call your plan's customer service number to find out what a specific drug costs under your coverage.
  • If your plan does not cover a drug your doctor prescribed, you can ask your doctor to request a coverage exception, which the plan must review within 72 hours.
  • Drugs are sorted into tiers that determine how much you pay — Tier 1 generics are cheapest, and specialty drugs are most expensive.
  • Your out-of-pocket costs change throughout the year as you move through the deductible, initial coverage, and catastrophic coverage phases.

How to learn about your drug is covered

The fastest way is to search your plan's formulary on Medicare.gov. Go to Medicare.gov/plan-compare, enter your zip code, select your current plan, and click "View Formulary." You can then search by drug name. The formulary will show you the tier your drug is in, any restrictions the plan places on it, and the cost you pay.

If you do not have internet access or prefer to speak with someone, call the customer service number on the back of your Medicare card. Have your prescription ready — include the drug name, strength, and how many pills or doses you take. The representative can tell you the cost and whether your doctor needs to get prior approval before the pharmacy can fill it.

If you are shopping for a new Part D plan during open enrollment (October 15 to December 7 each year), use the Medicare Plan Finder tool on Medicare.gov. Enter the drugs you take regularly, and the tool will show you which plans cover them and what your total costs would be under each plan. This is the only time you can switch plans without a penalty.

What the drug tiers mean and how much you pay

Part D plans organize drugs into tiers, and your copay or coinsurance depends on which tier your drug is in. Tier 1 includes generic drugs and is the cheapest — you might pay $5 to $10 per prescription. Tier 2 includes brand-name drugs with generic alternatives available, usually $15 to $50. Tier 3 includes brand-name drugs without a generic, often $50 to $100 or more. Tier 4 and Tier 5 are for specialty drugs — expensive medications for conditions like cancer, rheumatoid arthritis, or hepatitis C — and you may pay hundreds of dollars per prescription.

Some plans also use coinsurance instead of a flat copay, meaning you pay a percentage of the drug's cost (for example, 20 percent) rather than a fixed dollar amount. Your plan documents will specify which drugs use copays and which use coinsurance.

Your out-of-pocket costs also depend on which phase of coverage you are in during the calendar year. In the deductible phase (January through when you have spent your plan's deductible amount), you pay the full price of drugs. Once you meet the deductible, you enter initial coverage and pay your copay or coinsurance. After you and your plan together have spent a certain amount ($5,850 in 2024, though this changes yearly), you enter catastrophic coverage and pay a small copay while Medicare pays the rest.

When your plan will not cover a drug your doctor prescribed

If your drug is not on your plan's formulary, or if it is on the formulary but your plan requires prior approval and your doctor has not requested it, you have options. First, ask your doctor whether a similar drug in the same class is covered — for example, if your plan does not cover one blood pressure medication, it may cover another. Your doctor can check your formulary or call your plan to find an alternative.

If there is no suitable alternative, your doctor can request a coverage exception. This is a formal request asking the plan to cover a drug it normally would not. The plan must respond within 72 hours (or 24 hours in urgent cases). The plan may approve the exception, deny it, or approve it with conditions — for example, requiring you to try a cheaper drug first. If the plan denies the exception, you and your doctor can appeal the decision.

If you cannot wait for the exception process, you can pay out of pocket for the drug while the request is being reviewed. Keep your receipt — if the exception is approved, the plan may reimburse you for what you paid.

Restrictions your plan may place on covered drugs

Even if a drug is on your plan's formulary, the plan may limit how you can use it. Common restrictions include:

  • Prior authorization: Your doctor must get approval from the plan before the pharmacy can fill the prescription. This usually takes a few business days.
  • Quantity limits: The plan will only pay for a certain number of pills or doses per month. If you need more, you pay out of pocket or your doctor can request an exception.
  • Step therapy: You must try a cheaper or safer drug first. Only if that drug does not work can you move to the drug your doctor originally prescribed.
  • Preferred pharmacy: The plan pays more if you use certain pharmacies (usually mail-order or a chain's preferred location) and less if you use others.

Your plan's formulary document will list these restrictions next to each drug. If you see a restriction you do not understand, call your plan's customer service line.

Drugs Medicare Part D never covers

Federal law prohibits all Part D plans from covering certain categories of drugs, no matter which plan you choose:

  • Over-the-counter medications (aspirin, ibuprofen, cold medicines, antacids, and similar drugs you can buy without a prescription)
  • Drugs administered in a hospital, doctor's office, or clinic (these are covered under Part B instead)
  • Most vitamins and minerals, unless prescribed for a specific medical condition
  • Drugs prescribed for weight loss or cosmetic purposes
  • Drugs prescribed for erectile dysfunction (sildenafil, tadalafil)
  • Fertility drugs
  • Drugs used to treat infertility

Benzodiazepines (like alprazolam and diazepam) and barbiturates are covered by Part D, but plans have restrictions on them — typically limiting the quantity or requiring prior authorization. If you take one of these drugs, check your specific plan's formulary to see what restrictions explore.

What to ask your doctor and pharmacist

Before you fill a new prescription, ask your doctor: "Is this drug covered by Medicare Part D, and does my plan require prior authorization?" If your doctor is not sure, they can call your plan or check online. At the pharmacy, ask the pharmacist to show you the cost under your plan before you fill it — if it is higher than you expected, ask whether a generic or different drug would cost less.

If you are taking multiple drugs and your costs are high, ask your doctor or pharmacist whether any of them have generic versions or whether you can switch to a lower-tier drug that works the same way. Many people do not realize their plan covers a cheaper alternative to what they are taking.

When to contact your plan or Medicare

Contact your Part D plan's customer service if a drug you have been taking is suddenly not covered (this can happen when plans change their formularies each year), if you are denied a coverage exception and want to appeal, or if you are charged more than your plan says you should pay. You can also contact Medicare directly at 1-800-MEDICARE if you have a complaint about your plan or need help understanding your coverage.

If you are having trouble affording your medications even with Part D coverage, ask your pharmacist about patient information programs run by drug manufacturers. Many companies offer free or reduced-cost drugs to people who meet income requirements, and this coverage works alongside Medicare.

Frequently Asked Questions

Can I switch Part D plans if my drug is no longer covered?

You can switch plans during the annual open enrollment period (October 15 to December 7) without penalty. If your drug was covered when you enrolled but your plan removed it during the year, you may be able to switch outside of open enrollment — contact Medicare at 1-800-MEDICARE to ask about a special enrollment period.

What happens if I fill a prescription before checking whether it is covered?

If you pay out of pocket and the drug turns out to be covered, you can ask your plan for reimbursement. Keep your receipt and the pharmacy label. If the drug is not covered and you want it to be, ask your doctor to request a coverage exception while you still have the receipt.

Do generic drugs cost less than brand-name drugs under Part D?

Usually, yes — generics are typically in Tier 1 and cost $5 to $10, while brand-name drugs are in higher tiers. Ask your doctor whether a generic version of your drug is available and whether it would work as well for you. Many people can switch to a generic and save significantly.

If my plan covers a drug but requires prior authorization, how long does approval take?

Standard prior authorization takes up to 72 hours. If your doctor says the situation is urgent, the plan must respond within 24 hours. Ask your doctor's office to request expedited review if you need the drug right away.

Can I use a coupon or discount card for a drug my Part D plan covers?

Sometimes, but not always. Some coupons work alongside Medicare, and some do not. Ask your pharmacist to run both your Medicare card and any coupon to see which gives you the lower price. Do not assume the coupon is cheaper — your copay under Part D may be better.