Quick Answer
A Medicare Part D formulary is the official list of prescription drugs covered by your plan. Every Part D plan - whether a standalone Prescription Drug Plan (PDP) or a Medicare Advantage Prescription Drug plan (MAPD) - has its own formulary. Drugs are grouped into tiers, with lower tiers generally costing less. If your drug isn't on the formulary, you can request a formulary exception.
Coverage Comparison by Plan Type
| Plan Type | Coverage | Notes |
|---|---|---|
| Part A (Hospital) | Not Applicable | Part A covers inpatient drugs administered during a hospital stay, not retail prescriptions. |
| Part B (Medical) | Limited | Part B covers certain drugs administered in a clinical setting (e.g., chemotherapy, infusions). Most retail prescriptions fall under Part D. |
| Part D (PDP) | Formulary-Based | Standalone Part D plans have their own formulary. Coverage and cost depend on which tier your drug is assigned to. |
| Medicare Advantage (MAPD) | Formulary-Based | Most Medicare Advantage plans include Part D drug coverage with their own formulary. Costs vary by plan and tier. |
Understanding Your Coverage Options
How the Formulary Works
Every Medicare Part D plan must cover at least two drugs in each therapeutic category and class, but plans have flexibility in which specific drugs they include and how they tier them. CMS requires all Part D plans to cover drugs in six 'protected classes' - including antidepressants, antipsychotics, anticonvulsants, immunosuppressants, antiretrovirals, and antineoplastics - where plans must cover substantially all drugs in the class.
Formularies can change each year. Plans are required to notify enrollees of significant formulary changes at least 60 days before the change takes effect, or at the time of enrollment if you join mid-year. This is why reviewing your plan's Annual Notice of Change (ANOC) each fall is critical.
What It Covers
- All drugs listed on the plan's formulary, subject to tier-based cost-sharing
- At least two drugs per therapeutic category and class
- All drugs in the six CMS-protected classes
- Generic, brand-name, and specialty drugs (at different tiers)
What It Doesn't Cover
- Drugs not on the formulary (require a formulary exception)
- Over-the-counter medications (unless specifically listed)
- Drugs covered under Part A or Part B (e.g., hospital-administered drugs)
- Weight-loss drugs, fertility drugs, and cosmetic drugs
Six Protected Drug Classes
CMS requires Part D plans to cover substantially all drugs in six protected classes: antidepressants, antipsychotics, anticonvulsants, immunosuppressants, antiretrovirals, and antineoplastics. If you take a drug in one of these classes, your plan is very likely to cover it.
Drug Tiers Explained
Most Part D formularies use a 5-tier structure, though some plans use 4 or 6 tiers. The tier a drug is assigned to determines how much you pay - lower tiers mean lower cost-sharing. Generic drugs are almost always in lower tiers, while specialty drugs are in the highest tiers.
Your cost-sharing for each tier depends on your plan's specific benefit design. Some plans use flat copays per tier (e.g., $5 for Tier 1, $15 for Tier 2), while others use coinsurance (e.g., 25% of the drug's cost for Tier 3). Always check your plan's Evidence of Coverage (EOC) for the exact cost-sharing structure.
What It Covers
- Tier 1 - Preferred generics: lowest copay (typically $0–$10)
- Tier 2 - Non-preferred generics: low copay (typically $5–$20)
- Tier 3 - Preferred brand-name drugs: moderate cost (typically $35–$50)
- Tier 4 - Non-preferred brand-name drugs: higher cost (typically $60–$100+)
- Tier 5 - Specialty drugs: highest cost (typically 25–33% coinsurance)
What It Doesn't Cover
- Drugs not assigned to any tier (off-formulary drugs)
- Drugs subject to prior authorization until approval is granted
- Drugs subject to step therapy until lower-cost alternatives are tried first
$ Cost: Tier 1 generics often have $0 or very low copays. Specialty drugs (Tier 5) can cost hundreds of dollars per month even with coverage.
Prior Authorization and Step Therapy
Even if a drug is on your plan's formulary, your plan may require prior authorization (PA) before it will cover the drug. PA means your doctor must submit clinical documentation showing the drug is medically necessary for your condition. Common PA requirements apply to high-cost brand-name drugs and specialty medications.
Step therapy is a related restriction where your plan requires you to try a lower-cost drug first before it will cover a more expensive alternative. For example, your plan may require you to try a generic version of a drug before covering the brand-name version. If the first-line drug fails or causes side effects, your doctor can request a step therapy exception.
What It Covers
- Drugs after prior authorization is approved
- Brand-name drugs after step therapy requirements are met
- Exceptions granted when lower-cost alternatives are medically inappropriate
What It Doesn't Cover
- Drugs pending prior authorization (until approved)
- Brand-name drugs when a generic equivalent is required first (step therapy)
- Off-formulary drugs without an approved formulary exception
Always Check before Filling
Before starting a new prescription, use your plan's online drug lookup tool or call member services to confirm the drug is on your formulary and check for any prior authorization or step therapy requirements. Surprises at the pharmacy can be expensive.
Typical Part D Tier Cost Structure (2026)
| Tier | Drug Type | Typical Cost-Sharing | Examples |
|---|---|---|---|
| Tier 1 | Preferred generics | $0–$10 copay | Lisinopril, metformin, atorvastatin (generic) |
| Tier 2 | Non-preferred generics | $5–$20 copay | Generic drugs not on preferred list |
| Tier 3 | Preferred brand-name | $35–$50 copay | Eliquis (preferred), Jardiance (preferred) |
| Tier 4 | Non-preferred brand-name | $60–$100+ copay | Brand-name drugs with generic alternatives |
| Tier 5 | Specialty drugs | 25–33% coinsurance | Biologics, cancer drugs, MS medications |
✦ What to Do If Your Drug Isn't on the Formulary
Request a Formulary Exception
If your drug isn't on your plan's formulary, you can ask your plan for a formulary exception. Your doctor must submit a statement explaining why the formulary drug is not appropriate for your condition and why the non-formulary drug is medically necessary. Plans must respond within 72 hours for standard requests and 24 hours for urgent requests.
Your doctor must support the exception request with clinical documentation
Request a Tier Exception
If your drug is on the formulary but in a higher tier, you can request a tier exception to have it covered at a lower tier's cost-sharing. This is most useful for non-preferred brand-name drugs when a preferred alternative isn't medically appropriate for you.
Tier exceptions can significantly reduce your out-of-pocket costs
Switch Plans during Open Enrollment
If your current plan doesn't cover your drugs well, the Annual Enrollment Period (October 15 – December 7) is your opportunity to switch to a plan with a better formulary. Use Medicare's Plan Finder tool at Medicare.gov to compare plans based on your specific medications.
Use Medicare's Plan Finder to compare formularies before switching
How to Find and Review Your Plan's Formulary
Every Part D plan is required to make its formulary publicly available. You can find your plan's formulary on the plan's website, through Medicare's Plan Finder tool at Medicare.gov, or by calling your plan's member services line.
When reviewing a formulary, look up each of your current medications by name and check which tier they are assigned to. Also check for any restrictions like prior authorization or step therapy requirements. If you are comparing plans during open enrollment, Medicare's Plan Finder tool allows you to enter all your medications and compare estimated annual drug costs across multiple plans side by side.
Formulary Review Checklist
- List all your current prescriptions (name, dose, frequency)
- Look up each drug on your plan's formulary
- Note the tier assignment and cost-sharing for each drug
- Check for prior authorization or step therapy requirements
- Compare total estimated annual drug costs across plans
- Review your plan's Annual Notice of Change (ANOC) each fall
- Contact your doctor if a formulary exception may be needed
✦ Frequently Asked Questions
David Haass
AuthorDavid Haass is a Medicare content writer at MedicareFAQ with extensive experience explaining Medicare benefits, enrollment, and coverage options to beneficiaries.
Ashlee Zareczny
ReviewerAshlee Zareczny is the Compliance and Editorial Manager at MedicareFAQ, ensuring all Medicare content is accurate, up-to-date, and compliant with CMS guidelines.