The Basics of Medicare Part D Coverage

Medicare Part D covers prescription drugs — both brand-name and generic medications — through private insurance plans that contract with Medicare. Part D does not cover all drugs, and what you pay depends on which plan you choose and which drug you need. The plan you pick determines your costs, your pharmacy network, and whether a specific medication requires prior approval from your insurer before the pharmacy will fill it.

Part D is optional, but if you do not enroll when you first become may be able to access, you may pay a permanent penalty for every month you go without coverage. The penalty amount changes each year and is added to your premium for as long as you have Part D.

You obtain Part D coverage by joining a standalone Part D plan (if you have Original Medicare) or by choosing a Medicare Advantage plan that includes drug coverage. You can change plans once per year during the Annual Enrollment Period, which runs from October 15 to December 7.

Key Takeaways

  • Part D covers most prescription medications, but each plan maintains a formulary — a list of covered drugs — and you should check whether your specific medications are on it before you enroll.
  • All Part D plans charge a monthly premium, and most require you to pay a deductible before coverage begins, plus copayments or coinsurance when you fill prescriptions.
  • Part D does not cover over-the-counter drugs, vitamins, or medications used to treat erectile dysfunction, weight loss, or hair loss, with rare exceptions.
  • If your plan denies coverage for a drug your doctor prescribed, you can request an exception, and your doctor can appeal on your behalf.
  • Costs change at the beginning of each calendar year, so you should review your plan annually even if you were satisfied the previous year.

What Medications Part D Covers

Part D covers most prescription medications used to treat chronic and acute conditions. This includes antibiotics, blood pressure medications, diabetes drugs, heart medications, cancer treatments, mental health medications, and pain relievers. Brand-name drugs and their generic equivalents are both covered, though your out-of-pocket cost will usually be lower for generics.

Each Part D plan publishes a formulary — a detailed list of every drug the plan covers. The formulary also shows which tier each drug is on (tier 1 is usually the cheapest, tier 5 the most expensive), whether you need prior approval before filling it, and whether your doctor must request a step therapy (meaning you try a cheaper drug first). You can search your plan's formulary on Medicare.gov or call the plan directly to confirm a specific medication is covered before you enroll.

If your medication is not on the formulary, you have options. You can request a formulary exception from the plan, asking them to cover it anyway — your doctor must submit this request and explain why the drug is medically necessary. You can also switch to a different Part D plan during the Annual Enrollment Period if another plan covers your medication at a lower cost.

What Part D Does Not Cover

Part D explicitly excludes certain categories of drugs. Over-the-counter medications — such as ibuprofen, acetaminophen, antacids, and cold medicines — are not covered. Vitamins, minerals, and nutritional supplements are not covered. Drugs used to treat erectile dysfunction (such as sildenafil), weight loss (such as phentermine), and hair loss (such as finasteride) are not covered under Part D, though some plans may cover finasteride if prescribed for prostate conditions rather than baldness.

Part D also does not cover medications used solely for cosmetic purposes, drugs imported from outside the United States, and medications that your plan determines are not medically necessary. Benzodiazepines (such as diazepam) and barbiturates are subject to additional restrictions and may require prior approval or step therapy.

If you need a medication that Part D does not cover, you can pay out of pocket at the pharmacy's cash price, which often differs from what insurance would pay. Some pharmaceutical manufacturers offer patient information programs that provide free or reduced-cost medications to people who meet income requirements — your doctor or pharmacist can help you find these programs.

How Part D Costs Work Throughout the Year

Part D costs follow a predictable structure, though the exact amounts vary by plan and change each year. You pay a monthly premium to the insurance company. You also pay an annual deductible (the amount you must pay out of pocket before the plan begins to pay) — this deductible varies by plan and can range from zero to several hundred dollars.

Once you meet your deductible, you enter the initial coverage phase, where you pay a copayment or coinsurance for each prescription. Copayments are flat amounts (such as $5 for a generic drug), while coinsurance is a percentage of the drug's cost (such as 25 percent). As you fill prescriptions, your out-of-pocket costs accumulate.

When your total out-of-pocket spending reaches a certain threshold (the amount changes each year), you enter the coverage gap, sometimes called the "donut hole." In the coverage gap, you pay a higher percentage of the drug cost — currently 25 percent for most drugs — until your total out-of-pocket spending reaches the catastrophic threshold. Once you reach catastrophic coverage, the plan pays most of the cost and you pay only a small copayment or coinsurance per prescription for the rest of the year.

Prior Authorization and Step Therapy Requirements

Some medications require prior authorization — your doctor must contact the Part D plan and receive approval before the pharmacy will fill the prescription. Prior authorization is most common for expensive drugs, newer medications, or drugs typically used off-label. Your doctor's office usually handles this request, but it can add a few days to the process, so plan ahead if you need a refill.

Other drugs are subject to step therapy, meaning the plan requires you to try a cheaper or more standard medication first. If that drug does not work or causes side effects, your doctor can then request approval for the more expensive option. Step therapy is common for conditions like high cholesterol or depression, where multiple effective drugs exist at different price points.

If your plan denies coverage or requires step therapy for a drug your doctor believes is necessary, your doctor can file an appeal. The plan must respond within 72 hours for urgent appeals and 7 days for standard appeals. You can also request an independent review from an outside organization if you disagree with the plan's decision.

Choosing a Part D Plan and Reviewing Coverage

When you first become may be able to access for Medicare, you have a limited window to enroll in Part D without penalty — usually 63 days after your Medicare coverage begins. If you miss this window, you pay a permanent penalty unless you have other creditable coverage (such as from an employer or union). The penalty is calculated based on how many months you went without Part D and is added to your premium indefinitely.

To find Part D plans available in your area, use the Medicare Plan Finder tool on Medicare.gov. Enter your medications, preferred pharmacies, and doctors to see which plans cover them and what your costs would be. Plans vary significantly in premium, deductible, and copayment amounts, so comparing multiple options usually saves money. You can also call 1-800-MEDICARE to speak with a representative who can help you compare plans.

You should review your Part D plan every year during the Annual Enrollment Period, even if you were satisfied the previous year. Drug prices change, formularies change, and new plans enter the market. A plan that was cheapest last year may not be this year. You can switch to a different plan at any time during the Annual Enrollment Period (October 15 to December 7) with coverage beginning January 1.

What to Do If Your Medication Is Not Covered

If your Part D plan does not cover a medication your doctor prescribed, start by asking your doctor whether a covered alternative exists. Many conditions have multiple effective medications, and your doctor may be willing to prescribe a covered drug instead. Your pharmacist can also tell you which covered alternatives are available for your condition.

If no covered alternative is acceptable, request a formulary exception from your Part D plan. Your doctor must submit this request in writing, explaining why the uncovered drug is medically necessary and why covered alternatives will not work. The plan must respond within 72 hours for urgent requests and 7 days for standard requests. If the plan denies the exception, your doctor can appeal the decision.

If you cannot obtain coverage through your plan, check whether the drug manufacturer offers a patient information program. Many pharmaceutical companies provide medications free or at reduced cost to people with limited income. Your doctor's office, the manufacturer's website, or organizations like NeedyMeds.org can help you find these programs. You can also pay the pharmacy's cash price, though this is often more expensive than what insurance would pay.

Frequently Asked Questions

Can I use my Part D coverage at any pharmacy?

No. Each Part D plan has a network of preferred pharmacies where your copayments are lowest. You can use out-of-network pharmacies, but you will pay more. Some plans cover mail-order pharmacies for 90-day supplies at a lower cost per dose. Check your plan's pharmacy network before you enroll or call the plan to confirm your preferred pharmacy is in-network.

What happens to my Part D coverage if I move to a different state?

Your current Part D plan may not be available in your new state. You can switch to a different plan during the Annual Enrollment Period, or if you move, you may be able to change plans outside the enrollment period. Contact your current plan and Medicare to confirm your options and when you must switch.

Do I have to pay the Part D penalty if I had other drug coverage?

No. If you had creditable coverage — drug coverage from an employer, union, Veterans Affairs, or other source that is at least as good as Part D — you do not owe a penalty when you enroll in Part D later. You must keep records proving you had creditable coverage. If you are unsure whether your coverage was creditable, contact your former employer or insurance company.

Can my Part D plan change my formulary during the year?

Yes, though plans must notify you before removing a drug you are currently taking. If your plan removes a medication you depend on, you can request a formulary exception or switch to a different plan outside the normal enrollment period. Contact your plan when ready if you receive notice that your medication is being removed.

What if I cannot afford my Part D copayments?

If your income is low, you may may have access to for the Part D Low-Income Subsidy, which reduces your premiums, deductibles, and copayments. You can explore through your local Social Security office or Medicaid agency. Some pharmaceutical manufacturers also offer copayment information cards that reduce your out-of-pocket cost at the pharmacy.