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 what Georgia seniors need to know before choosing a 2026 plan.

Author: Lynsey Brennan, Licensed Medicare Advisor | Published August 04, 2026 Reading time: 6 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 standalone or bundled inside a Medicare Advantage plan — has its own formulary, which means the same drug can cost very different amounts depending on which plan you choose. Checking the formulary before you enroll is one of the most practical things you can do for your budget.

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Key Takeaways

• Every Part D plan maintains its own drug list, organized into tiers that directly affect what you pay at the pharmacy.
• Starting in 2025, the Inflation Reduction Act capped out-of-pocket drug costs at $2,000 per year for Part D enrollees (CMS, 2025).
• Covered insulin is capped at $35/month under Medicare Part D, regardless of tier.
• Formularies can change each year during the Annual Enrollment Period — reviewing your plan every fall is worth your time. See our Part D drug coverage guide for a deeper look.
• Georgia Medicare enrollees should compare both standalone PDPs and Medicare Advantage plans that include drug coverage, since formularies vary widely by carrier and county.

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Table of Contents

1. What a Formulary Actually Is 2. How Drug Tiers Work — and Why They Affect Your Wallet 3. Formulary Rules Specific to 2026 Plans 4. What Georgia Seniors Should Watch For 5. How to Check If Your Drugs Are Covered 6. When a Formulary Change Affects You Mid-Year 7. Formulary vs. the Bigger Coverage Picture

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What a Formulary Actually Is {#what-a-formulary-actually-is}

Think of a formulary as a contract between you and your drug plan. The plan says: "We will help pay for these drugs, at these prices, under these conditions." If your medication is on the list, great — you pay your cost-sharing amount. If it is not, you are typically paying full price out of pocket.

CMS requires every Part D plan to cover at least two drugs in most therapeutic categories, but beyond that baseline, plans have real flexibility to include or exclude specific brand-name and generic options. That flexibility is why comparing plans on actual drug coverage — not just premium — matters so much.

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How Drug Tiers Work — and Why They Affect Your Wallet {#how-drug-tiers-work}

Most Part D formularies use a five-tier structure, though some plans use four or six tiers. The lower the tier number, the less you typically pay:

• Tier 1 — Preferred generics: Usually the lowest copay, often just a few dollars.
• Tier 2 — Non-preferred generics: Still affordable, but higher than Tier 1.
• Tier 3 — Preferred brand-name drugs: Moderate cost-sharing; often requires a higher copay.
• Tier 4 — Non-preferred drugs: Noticeably higher cost; sometimes includes specialty generics.
• Tier 5 — Specialty drugs: The highest cost-sharing tier, reserved for high-cost medications like biologics.

A drug your doctor has prescribed for years might sit on Tier 1 in one plan and Tier 4 in another. That gap could mean hundreds of dollars difference over a year, even before you reach the $2,000 out-of-pocket cap.

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Formulary Rules Specific to 2026 Plans {#formulary-rules-2026}

The Inflation Reduction Act changed Part D in meaningful ways. Starting in 2025 and continuing into 2026, the annual out-of-pocket cap is $2,000 per CMS (2025). Once you hit that amount, the plan covers 100% of covered drug costs for the rest of the calendar year. The old "donut hole" coverage gap has been eliminated.

Insulin coverage is also specifically protected: covered insulin is capped at $35/month under Medicare Part D, regardless of what tier the plan places it on.

These protections apply only to drugs on the formulary. A plan can still require prior authorization, quantity limits, or step therapy (meaning you try a cheaper drug before the plan approves a more expensive one) for covered medications. These are called utilization management tools, and they are completely legal. When you review a plan, look at both whether a drug is covered and whether restrictions apply.

For a full breakdown of what Part D covers, see our Part D drug coverage guide.

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What Georgia Seniors Should Watch For {#what-georgia-seniors-should-watch-for}

Georgia Medicare enrollees have a range of plan options that can vary significantly by county. In metro Atlanta, for example, multiple insurance carriers offer both standalone Part D plans (PDPs) and Medicare Advantage plans with drug coverage (MA-PDPs), and formularies differ across all of them.

One thing Georgia seniors often overlook: if you have a Medicare Supplement (Medigap) policy, you cannot bundle drug coverage into it — you need a separate standalone PDP. If you have a Medicare Advantage plan, drug coverage is often included, but you must confirm it. Our Medicare Advantage vs. Supplement comparison breaks down how these two approaches differ in cost and structure.

For a broader look at how Georgia fits into national Medicare enrollment trends — nationally, about 54% of Medicare beneficiaries are enrolled in Medicare Advantage per CMS (2024) — and what that means for your local plan options, our Medicare Advantage guide is a useful starting point.

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How to Check If Your Drugs Are Covered {#how-to-check-if-your-drugs-are-covered}

Before Annual Enrollment Period (AEP) opens each October 15, gather a list of every medication you take — including dosage and frequency. Then:

1. Use the Medicare Plan Finder at medicare.gov or our plan comparison tool to enter your drugs and pharmacy. 2. Look not just at whether the drug is covered, but which tier it falls on and whether prior authorization or quantity limits apply. 3. Confirm that your preferred pharmacy is in-network. Many plans charge less at preferred pharmacies.

If a drug you need is not on a plan's formulary, you can request a formulary exception. Plans are required to have an exceptions process, and your doctor can submit supporting documentation. Exceptions are not guaranteed, but they are worth pursuing.

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When a Formulary Change Affects You Mid-Year {#when-a-formulary-change-affects-you-mid-year}

Plans can generally change their formulary during the year, but CMS rules do offer some protection. If a drug you are actively taking is removed from the formulary mid-year, the plan must typically give you at least 60 days' notice or continue covering the drug through the end of the year if you are already taking it for a chronic condition.

This is also a key reason to review your plan during AEP each fall, even if you feel fine with your current coverage. A drug that was well-covered in 2026 may shift to a higher tier — or drop off entirely — in 2027. For a refresher on enrollment windows and deadlines, see our Medicare enrollment periods guide.

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Formulary vs. the Bigger Coverage Picture {#formulary-vs-the-bigger-coverage-picture}

The formulary is one piece of a larger puzzle. Drug costs interact with your Part B premium ($185/month in 2026, per CMS November 2025), your deductible, and — if you have a Medicare Advantage plan — the plan's out-of-pocket maximum, which is capped at $9,350 for in-network services in 2026 per CMS (2025).

See our 2026 Medicare costs page for a plain-language breakdown of what you are likely to pay across all parts of Medicare. And if you are still deciding between a Medicare Advantage plan and a Medicare Supplement policy, our Medicare Advantage vs. Supplement guide walks through the honest trade-offs of each.

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Frequently Asked Questions

Q: Can a Medicare Part D plan change its formulary after I enroll? A: Yes, plans can make certain formulary changes during the year, though CMS rules require advance notice for drugs you are currently taking. The most significant changes typically take effect January 1, which is why reviewing your plan each fall during AEP is a good habit.

Q: What happens if my doctor prescribes a drug that is not on my plan's formulary? A: You can request a formulary exception through your plan's appeals process. Your doctor will need to submit a statement explaining why the drug is medically necessary. Plans are required to have this process, but approval is not guaranteed.

Q: Does the $2,000 out-of-pocket cap apply to all drugs or just formulary drugs? A: The $2,000 annual cap applies to covered drugs on your plan's formulary. If a drug is not on the formulary and no exception has been approved, costs for that drug typically do not count toward the cap.

Q: Do Medicare Supplement (Medigap) plans include drug coverage? A: No. Medigap plans do not include prescription drug coverage. If you have a Medigap policy, you need a separate standalone Part D plan to get drug coverage. See our Medicare Supplement guide for more detail on what Medigap does and does not cover.

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The Bottom Line

Your Part D formulary is not fine print — it is a direct driver of what you pay for prescriptions every month. The tier your medications fall on, whether prior authorization is required, and how the plan's costs stack up against alternatives can all affect your real-world expenses. A licensed Medicare advisor can pull the actual formulary data for plans in your Georgia county and walk through how your specific drugs are covered before you commit.

Ready to get a clear picture of your options? Schedule a free Medicare review with HealthPlan Connect today — no pressure, just straight answers tailored to your situation.

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Sources

• CMS Medicare Monthly Enrollment, 2024
• CMS Medicare Part D Formulary Requirements, 2025
• CMS 2026 Medicare Advantage and Part D Rate Announcement, 2025
• CMS Medicare Part B Premium and Deductible Announcement, November 2025
• Inflation Reduction Act, Medicare Drug Price Negotiation and Out-of-Pocket Cap Provisions, 2022
• CMS Medicare Plan Finder (medicare.gov)
• KFF Medicare Part D Overview, 2025

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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.