Medicare Part D (Prescription Drug Coverage)

Medicare Part D is the prescription drug benefit program that helps Medicare beneficiaries pay for outpatient medications. Part D plans are offered by private insurance companies approved by Medicare and are available as standalone Prescription Drug Plans (PDPs) for those with Original Medicare, or as part of Medicare Advantage plans.

The Part D program was established by the Medicare Modernization Act of 2003 and took effect in January 2006. A major improvement beginning in 2025 is the $2,000 annual out-of-pocket cap on prescription drug spending, eliminating the catastrophic coverage phase burden for beneficiaries.

Each Part D plan has its own formulary (list of covered drugs), which is organized into tiers with different cost-sharing levels. Plans must cover at least two drugs in each therapeutic category and all drugs in six protected classes including cancer, HIV/AIDS, and anti-seizure medications.

What Part D Covers

• Brand-name and generic prescription drugs listed on the plan's formulary
• All commercially available vaccines (covered at $0 cost-sharing as of 2023)
• Insulin products capped at $35/month per prescription
• Some biosimilar medications
• Medications across all therapeutic categories

Six Protected Drug Classes (All Drugs Covered)

• Anticonvulsants (seizure medications)
• Antidepressants
• Antineoplastics (cancer drugs)
• Antipsychotics
• Antiretrovirals (HIV/AIDS drugs)
• Immunosuppressants (organ rejection prevention)

What Part D Does NOT Cover

• Drugs covered under Part A or Part B (e.g., drugs administered in a hospital or doctor's office)
• Over-the-counter medications
• Vitamins and supplements (except prenatal vitamins and fluoride preparations)
• Drugs for weight loss or cosmetic purposes
• Drugs purchased outside the United States

Who Qualifies for Medicare Part D

• Anyone enrolled in Medicare Part A or Part B is eligible for Part D
• Must live in the Part D plan's service area
• Must be a U.S. citizen or lawfully present

Part D enrollment is voluntary but strongly recommended. If you go 63 or more consecutive days without creditable prescription drug coverage (coverage at least as good as Part D), you may face a late enrollment penalty of 1% of the national base premium per month of delay, added permanently to your premium.

Low-income beneficiaries may qualify for Extra Help (Low-Income Subsidy), which significantly reduces premiums, deductibles, and copays.

2025/2026 Part D Costs

• National Base Premium: $36.78/month in 2025 (actual premiums vary by plan, averaging around $40-$55/month)
• Annual Deductible: Up to $590 in 2025 (many plans have lower or $0 deductibles)
• Annual Out-of-Pocket Cap: $2,000 in 2025 (NEW — eliminates the previous catastrophic phase burden)
• Medicare Prescription Payment Plan: Option to spread out-of-pocket costs evenly across the year in monthly payments
• Insulin: Capped at $35/month per covered insulin product

Typical Formulary Tiers

• Tier 1 (Preferred Generic): $0-$15 copay
• Tier 2 (Generic): $5-$22 copay
• Tier 3 (Preferred Brand): $35-$50 copay
• Tier 4 (Non-Preferred Brand): 30-40% coinsurance
• Tier 5 (Specialty): 25-33% coinsurance

How to Enroll

• Initial Enrollment Period (IEP): 7-month window around your 65th birthday (same as Part B)
• Annual Enrollment Period (AEP): October 15 through December 7 each year for coverage starting January 1
• Special Enrollment Periods: Available for losing creditable coverage, moving, qualifying for Extra Help, or other life events
• Medicare Advantage Open Enrollment: January 1 through March 31 — you can switch to an MA plan with drug coverage

Compare plans using the Medicare Plan Finder at Medicare.gov/plan-compare. Enter your specific medications to find the plan with the lowest total cost. You can also call 1-800-MEDICARE or contact your State Health Insurance Assistance Program (SHIP).

Pros

• New $2,000 annual out-of-pocket cap starting in 2025 dramatically reduces catastrophic drug costs
• Insulin capped at $35/month regardless of plan tier
• All vaccines covered at $0 cost-sharing
• Medicare Prescription Payment Plan allows spreading costs across the year
• Extra Help program available for low-income beneficiaries
• Wide selection of plans allows choosing based on your specific medications

Cons

• Monthly premium required in addition to Part B premium
• Formularies vary by plan — your specific drug may not be covered or may be on a high tier
• Plans can change formularies and pricing annually
• Prior authorization and step therapy requirements may delay access to certain medications
• Late enrollment penalty is permanent if you go without creditable coverage