What Is the Medicare Part D Formulary and Why Does It Matter?

Learn what a Medicare Part D formulary is, how drug tiers affect your costs, and why checking your plan's drug list before Open Enrollment can matter.

Author: Lynsey Brennan, Licensed Medicare Advisor | Published September 29, 2026 Reading time: 7 min read

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Quick Answer

A Medicare Part D formulary is the list of prescription drugs a specific plan agrees to cover. Every Part D plan — whether it's a standalone drug plan or drug coverage bundled into a Medicare Advantage plan — has its own formulary, and what's covered (and what it costs you) can vary significantly from one plan to the next. Checking your formulary before Open Enrollment each year is one of the most practical things you can do to avoid surprise drug costs.

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Key Takeaways

• Every Part D plan has its own formulary; your drug may be covered on one plan and not another.
• Drugs are sorted into "tiers" — lower tiers typically mean lower copays for you.
• Formularies can change year to year, even if you stay in the same plan.
• The 2026 Part D out-of-pocket cap for covered drugs is $2,100 (CMS CY 2026 Part D benefit parameters).
• Florida seniors have dozens of Part D plan options — comparing them annually with a licensed Medicare advisor or the plan comparison tool is worth the time.

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Table of Contents

• What a Formulary Actually Is
• How Drug Tiers Work and What They Cost You
• Why Formularies Change Every Year
• Florida-Specific: What Part D Looks Like Here
• Special Protections Worth Knowing
• How to Check If Your Drugs Are Covered
• Formulary vs. Medicare Supplement: What's the Difference?

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What a Formulary Actually Is

Think of a formulary as a plan's approved drug list. Insurance companies that offer Part D coverage negotiate directly with drug manufacturers, which is why each plan ends up with a somewhat different list of covered medications.

CMS requires every Part D plan to cover at least two drugs in each therapeutic category — meaning that if you take a common blood pressure medication, some version of it will likely be covered. But "some version" is the key phrase. Your specific brand-name drug or dosage may sit on a high-cost tier, require prior authorization, or not appear on the formulary at all.

You can dig deeper into how Part D works from the ground up in our Part D drug coverage guide.

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How Drug Tiers Work and What They Cost You

Most Part D plans organize their formulary into five tiers. The structure typically looks like this:

• Tier 1: Preferred generic drugs — usually the lowest copay
• Tier 2: Non-preferred generic drugs — slightly higher copay
• Tier 3: Preferred brand-name drugs — moderate cost-sharing
• Tier 4: Non-preferred brand-name drugs — higher out-of-pocket cost
• Tier 5: Specialty drugs — often the highest cost, sometimes a percentage of the drug price rather than a flat copay

The exact dollar amounts vary by plan. A Tier 3 drug on Plan A might cost you $42 per fill; the same drug on Plan B might cost $75. That difference adds up fast over 12 months.

One important protection: covered insulin under Part D is capped at $35 per month per CMS rules, regardless of which tier it sits on. If you take insulin, that cap applies whether you're enrolled in a standalone Part D plan or a Medicare Advantage plan with drug coverage.

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Why Formularies Change Every Year

Part D plans are allowed — and required by CMS — to update their formularies annually. A drug that was on your plan's Tier 2 this year could move to Tier 4 next year, or be removed from the formulary entirely. This is completely legal.

Plans are supposed to notify enrollees about significant formulary changes before October 1 each year, so you receive that notice before Open Enrollment (October 15 - December 7). The honest reality is that these notices can be easy to overlook.

This is exactly why a quick annual review matters. See our Medicare enrollment periods page for the full Open Enrollment timeline and what you can change and when.

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Florida-Specific: What Part D Looks Like Here

Florida has one of the most competitive Medicare markets in the country. According to CMS Medicare Monthly Enrollment data from 2024, 56.1% of Florida Medicare beneficiaries are enrolled in Medicare Advantage — and most of those plans include drug coverage (called MA-PD plans). That means the formulary question often comes bundled with the broader question of which Advantage plan you're on.

For Florida seniors on standalone Part D plans, the number of available plans in any given county can range from the mid-teens to over 20 options, depending on your zip code. More options can be useful, but only if you're comparing them against your actual drug list. You can see how Florida stacks up overall at our Florida Medicare data page.

One practical note for Floridians: if you split time between Florida and another state, make sure your plan's pharmacy network covers your drugs in both locations, or consider a plan with broader mail-order options.

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Special Protections Worth Knowing

A few federal rules work in your favor when it comes to formularies:

Exceptions and appeals. If your drug isn't covered or is on a higher tier than you think is fair, you have the right to request a formulary exception. Your doctor would need to document that the covered alternative isn't appropriate for your condition. This process takes time, so starting early matters.

Protected drug classes. CMS requires Part D plans to cover "all or substantially all" drugs in six protected classes: immunosuppressants, antidepressants, antipsychotics, anticonvulsants, antiretrovirals, and antineoplastics. If you take any of these, your plan has a higher bar to clear before it can restrict your access.

The $2,100 out-of-pocket cap. Starting in 2026, once you spend $2,100 out of pocket on covered Part D drugs in a calendar year, your cost-sharing for covered drugs drops to $0 for the rest of the year (per CMS CY 2026 Part D benefit parameters). This is a meaningful protection, especially for people managing multiple prescriptions or high-cost specialty drugs.

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How to Check If Your Drugs Are Covered

The most reliable way to check is to use Medicare's Plan Finder at medicare.gov, where you can enter your specific drugs — including dosage and quantity — and see which plans cover them and at what tier and cost. You can also use our plan comparison tool for side-by-side help.

When you're reviewing a plan, look at three things together: the monthly premium, the tier placement of your drugs, and the pharmacy network (are your preferred pharmacies in-network?). A low-premium plan can end up costing more overall if your drugs land on high tiers.

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Formulary vs. Medicare Supplement: What's the Difference?

Medicare Supplement (Medigap) plans don't include drug coverage — they're designed to cover cost-sharing gaps in Original Medicare (Parts A and B). If you're on a Medigap plan, you'd pair it with a separate standalone Part D plan for prescriptions.

Medicare Advantage plans, on the other hand, often bundle drug coverage together. This can simplify billing, but it also means your drug coverage is tied to that specific plan's formulary. Switching plans could change your drug costs significantly.

Understanding this distinction matters when you're deciding which coverage path fits you. Our Medicare Advantage vs. Supplement comparison and Medicare Advantage guide walk through the real trade-offs honestly.

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Frequently Asked Questions

Q: Can a Part D plan remove my drug from the formulary mid-year? A: Generally, no. Plans can't remove a drug mid-year unless the FDA withdraws it from the market or CMS approves the change. If your drug is removed at the start of a new plan year, you'll typically be notified before Open Enrollment so you can switch plans if needed.

Q: What if my doctor prescribes a drug that's not on my plan's formulary? A: You can request a formulary exception, which requires your doctor to submit documentation explaining why the covered alternatives aren't appropriate for your condition. The plan must respond within a set timeframe — 72 hours for standard requests, 24 hours for urgent situations.

Q: Does the $2,100 Part D out-of-pocket cap apply to all my drugs? A: The $2,100 cap applies to covered Part D drugs per CMS CY 2026 Part D benefit parameters. Drugs that aren't on your plan's formulary, or that you purchase outside the plan's network, typically don't count toward that cap, which is one more reason why formulary coverage matters.

Q: Is the formulary the same for every Medicare Advantage plan in Florida? A: No — each plan sets its own formulary. Two Medicare Advantage plans offered by the same insurance company in the same Florida county can have different formularies, different tier placements, and different copays for the same drug. Always check your specific drugs against the specific plan you're considering.

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The Bottom Line

A formulary isn't fine print — it's one of the most practical things to check before you pick or stick with a Part D plan. Tier changes and formulary updates happen every year, and the only way to know if your current plan still makes sense is to look. If you'd like help comparing your drug costs across plans available in your area, I'm happy to walk through it with you at no charge. Schedule a free Medicare review and we'll start with what you're actually taking.

Questions? Call or text: 561-247-0678

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Sources

• CMS Medicare Monthly Enrollment, 2024
• CMS CY 2026 Part D Benefit Parameters (published 2025)
• CMS, Medicare Part D Formulary Requirements and Protected Drug Classes
• CMS, November 2025 — 2026 Medicare Part B Premium and Deductible Announcement
• Medicare.gov, Plan Finder and formulary exception guidance

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This article is for educational purposes and is not affiliated with or endorsed by the federal Medicare program or any government agency. HealthPlan Connect is a private, licensed Medicare advisory service. FL License #G007269.