Quick Answer
A Medicare Part D formulary is the list of covered prescription drugs for a specific plan. Drugs are grouped into tiers - typically 5 - with lower tiers costing less and higher tiers costing more. Every Part D plan must cover drugs in six protected classes, but plans can choose which other drugs to include. You should always check that your medications are on a plan's formulary before enrolling.
Coverage Comparison by Plan Type
| Plan Type | Coverage | Notes |
|---|---|---|
| Medicare Part D (Standalone) | Covered | Each plan has its own formulary; tiers determine your copay or coinsurance |
| Medicare Advantage with Part D (MAPD) | Covered | MA-PD plans have their own formulary; must meet same CMS requirements |
| Original Medicare (Part A & B) | Not Applicable | Original Medicare does not cover most outpatient prescription drugs |
| Medicare Supplement (Medigap) | Not Applicable | Medigap does not cover drugs; you need a separate Part D plan |
Understanding Your Coverage Options
How Formulary Tiers Work
Most Part D formularies use a 5-tier structure. Tier 1 covers preferred generic drugs at the lowest cost. Tier 2 covers non-preferred generics. Tier 3 covers preferred brand-name drugs. Tier 4 covers non-preferred brand-name drugs at a higher cost. Tier 5 covers specialty drugs - typically high-cost biologics and specialty medications - at the highest cost-sharing level.
Your copay or coinsurance for each drug depends on its tier and your plan's specific cost structure. Always check the plan's formulary before enrolling to confirm your medications are covered and at what tier.
Formulary Protections and Exceptions
All Part D plans must cover all or substantially all drugs in six protected classes: antidepressants, antipsychotics, anticonvulsants, antiretrovirals, immunosuppressants, and antineoplastics. For other drugs, plans have flexibility in what they include.
If your drug is not on a plan's formulary, you can request a formulary exception. Your doctor must provide documentation that the drug is medically necessary. Plans are required to respond to exception requests within 72 hours (or 24 hours for urgent requests).
Checking Your Formulary
You can find a plan's formulary on Medicare.gov's Plan Finder tool or directly on the plan's website. Enter your medications to see which plans cover them and at what cost. Plans can change their formularies each year, so it is important to review your coverage during the Annual Enrollment Period (October 15 – December 7) each year.
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David Haass
AuthorDavid Haass is the Chief Technology Officer and Co-Founder of Elite Insurance Partners and MedicareFAQ.com. He is a member and regular contributor to Forbes Finance Council.
Ashlee Zareczny
ReviewerAshlee Zareczny is a licensed Medicare agent in all 50 states dedicated to educating those eligible for Medicare. She trains agents on CMS compliance guidelines.