Medicare Part D Formulary Guide (2026): Drug Tiers, Exceptions, and Switching Plans

Best for Medicare beneficiaries who take brand or specialty drugs and need predictable pharmacy costs. Part D plans change formularies annually—verify your medications every fall, not only at initial enrollment.

How formularies work

• Each plan publishes a drug list with tiers (generic, preferred brand, non-preferred, specialty).
• Tier placement drives copays or coinsurance—same drug can sit on different tiers across plans.
• Prior authorization (PA) and step therapy may be required before the plan pays.

Formulary exceptions

• Request an exception when your drug is not on the formulary or is on a high tier without a clinical equivalent.
• Physician statement of medical necessity is usually required—start with your prescriber, not the pharmacy.
• Appeal denied exceptions through the plan's Medicare appeals process with dated denial letters.

Part D vs Medigap drug coverage

Medigap policies sold today do not include standalone drug coverage—you need a Part D plan or Medicare Advantage with drug benefits. Medigap Plan letters help with cost-sharing for services, not pharmacy tiers. Cross-read /guides/medicare-medigap-plan-letters-deep-guide-2026 for hospital and physician gaps Part D does not fill.

Scenario: specialty drug on tier 5

A beneficiary takes a tier-5 specialty medication with 25% coinsurance until the Part D deductible and initial coverage limits apply. Comparing three plans during Open Enrollment shows one plan places the drug on tier 3 with a fixed copay—annual savings can exceed $2,000 despite higher monthly premium.

Scenario: drug removed mid-year

A plan drops a maintenance drug from the formulary effective July 1. Beneficiaries may qualify for a one-time Special Enrollment Period or formulary exception for continuity of therapy—file before switching pharmacies to avoid cash-pay gaps.

Buying checklist

• Run every prescription through the plan's online formulary search before enrolling.
• Check mail-order vs retail pricing for 90-day supplies.
• Confirm pharmacy network includes your preferred location.
• Review /guides/medicare-annual-enrollment-timing-guide-2026 for switch deadlines.
• Billing disputes on EOB codes: /claims/guides/medicare-billing-error-claim-guide-2026.

FAQ

Q: Can I use GoodRx instead of Part D? A: You can, but cash prices do not count toward Part D catastrophic coverage—model total annual cost both ways.

Q: What is the Part D deductible in 2026? A: Plans may charge up to the annual cap set by CMS—compare premium plus deductible, not premium alone.

Q: Do supplements cover insulin? A: Standard Medigap does not cover retail pharmacy drugs—you need Part D or qualifying Advantage drug coverage.

Related guides

• Medigap plan letters: /guides/medicare-medigap-plan-letters-deep-guide-2026
• Annual enrollment timing: /guides/medicare-annual-enrollment-timing-guide-2026
• Compare Medicare products: /insurance/medicare