Medicare Part D is the portion of Medicare that helps cover the cost of outpatient prescription medications. Unlike Parts A and B, which are provided directly through the federal government, Part D coverage is offered through private insurance companies approved by Medicare.

You can receive Part D benefits in one of two ways:

• Through a stand-alone Prescription Drug Plan (PDP) if you are enrolled in Original Medicare
• As part of a Medicare Advantage plan (MAPD) that includes prescription drug coverage

When Should You Enroll?

It’s important to sign up for Part D when you first become eligible for Medicare. Unless you already have “creditable” prescription drug coverage or qualify for a Special Enrollment Period, delaying enrollment can lead to:

• Gaps in prescription coverage
• Late enrollment penalties
• Higher premiums in the future

Enrolling on time helps ensure you have access to the medications you need without unnecessary added costs.

How Part D Plans Work

Each Medicare Part D plan has its own list of covered medications, known as a formulary. The formulary outlines which drugs are covered and at what cost level.

If a medication you need is not included on your plan’s formulary, you still have options. You may be able to:

• Request an exception
• File an appeal
• Pay out of pocket
• Work with your doctor to find a covered alternative

Because formularies can vary widely from plan to plan, it’s important to review coverage carefully when choosing or renewing a Part D plan.

Required Drug Coverage

Part D plans are required to cover a broad range of medications. Drugs are organized into categories based on the conditions they treat or how they work in the body. Every Part D plan must include at least two drugs from most categories.

In addition, all Part D plans must cover all or substantially all medications in the following protected classes:

• HIV/AIDS treatments
• Antidepressants
• Antipsychotic medications
• Anticonvulsive treatments for seizure disorders
• Immunosuppressant drugs
• Anticancer drugs (unless they are covered under Medicare Part B)

Part D plans are also required to cover most vaccines, with the exception of those already covered under Medicare Part B.

What Part D Does Not Cover

Not all medications are eligible for coverage under Medicare Part D. By law, certain types of drugs are excluded, including:

• Medications used for weight loss or weight gain
• Over-the-counter drugs
• Certain cosmetic or lifestyle medications

It’s also important to note that in some situations, specific medications may be covered under Medicare Part A or Part B rather than Part D, depending on how and where they are administered.

Choosing the Right Plan

Because each Part D plan has its own formulary, premiums, and cost-sharing structure, the best plan for one person may not be the best for another. Reviewing your current medications and comparing available plans each year can help ensure you continue to get the most affordable and appropriate coverage.

Understanding how Medicare Part D works—and enrolling at the right time—can help protect both your health and your budget.