Medicare Part D Formularies: How Generic Coverage Works in 2026

When you're on Medicare and need prescription drugs, your formulary isn't just a list-it's the key to how much you pay each month. For most beneficiaries, generic drugs are the backbone of their coverage. In fact, 92% of all prescriptions filled under Medicare Part D in 2023 were for generics. But understanding how these drugs are covered, priced, and prioritized can make a huge difference in your out-of-pocket costs-especially now that major changes took effect in 2025.

How Medicare Part D Formularies Are Built

Medicare Part D formularies are created by private insurance companies, but they don’t get to make the rules. Every plan must follow strict federal guidelines set by the Centers for Medicare & Medicaid Services (CMS). These rules ensure that beneficiaries have access to a wide range of medications, especially generics.

Each formulary must include at least two different generic drugs in every major therapeutic class. For example, if you take a blood pressure medication, your plan must offer at least two different generic versions of that drug. This isn’t just about choice-it’s about competition. More options mean lower prices.

Plans also have to cover at least 85% of the drugs in each therapeutic class. For six critical categories-like antidepressants, antiretrovirals, and antineoplastics-they must cover 100% of available generics. This protects people with serious or chronic conditions from being left without affordable options.

The formulary is managed by a Pharmacy and Therapeutics (P&T) Committee. This group includes at least half practicing doctors and pharmacists who review clinical data, cost-effectiveness, and patient outcomes before deciding which drugs make the list. It’s not just about what’s cheapest-it’s about what actually works.

The Five-Tier System: Where Generics Fit In

Medicare Part D plans organize drugs into five tiers, and generics mostly live in the first two.

• Tier 1: Preferred generics. These are the cheapest options. Most plans charge $0 to $15 for a 30-day supply. You’ll often see drugs like lisinopril (for blood pressure), metformin (for diabetes), or atorvastatin (for cholesterol) here.
• Tier 2: Non-preferred generics. These are still generic, but not the plan’s top pick. You might pay 25-35% coinsurance or a fixed copay up to $40. This tier often includes newer generics or ones with slightly higher costs.
• Tiers 3-5: These are mostly brand-name drugs and specialty medications. Generics rarely appear here, unless they’re high-cost specialty drugs like those used for rare conditions.

The placement matters because it directly affects your costs. A drug on Tier 1 might cost you $5 a month. The same drug on Tier 2 could cost $35. That’s a $300 difference over a year-just from switching tiers.

How Much You Pay in 2026

The way you pay for generics changed dramatically in 2025 thanks to the Inflation Reduction Act. Before that, beneficiaries hit a "donut hole"-a gap where they paid full price after reaching a certain spending limit. That’s gone now.

Here’s how it works in 2026:

1. Deductible: You pay the first $615 of drug costs in 2025 (it’s $630 in 2026). Some plans have a $0 deductible, so check yours.
2. Initial coverage: After the deductible, you pay 25% of the cost for generics. The plan pays the rest. This continues until your total out-of-pocket spending hits $2,100 in 2026.
3. Catastrophic coverage: Once you hit the $2,100 cap, you pay $0 for all drugs-generics and brands-for the rest of the year. That’s right: no more coinsurance, no more copays.

What’s surprising is that for generics, only what you actually pay counts toward that $2,100 cap. For brand-name drugs, the plan counts 70% of the drug’s total cost toward your cap-even if you didn’t pay it. That’s because manufacturers give discounts. This means you can hit the cap faster with generics if you’re taking multiple drugs.

Why Generics Are So Much Cheaper

Generics make up 92% of prescriptions but only 18% of total drug spending under Part D. That’s because they cost far less to produce. Once a brand-name drug’s patent expires, other companies can make the same active ingredient. They don’t need to repeat expensive clinical trials. That’s why a generic version of a drug that once cost $200 a month might now cost $5.

But here’s the catch: even though generics are cheaper, they’re not always the same in your plan. Two drugs might have the same active ingredient-say, metoprolol for heart conditions-but if your plan only covers one version, you might be stuck paying full price for the other. That’s called "therapeutic interchange," and it’s a common source of confusion.

A 2024 survey by the Medicare Rights Center found that 62% of people using generics understood their plan’s tier system. Only 42% of brand-name users did. The reason? Generics are simpler. Fewer restrictions. Lower costs. But if your plan doesn’t cover the exact generic you’re used to, you’re in trouble.

What You Need to Do Right Now

You can’t just assume your coverage stays the same. Every fall, plans send out an Annual Notice of Change. This document tells you if your drugs are moving tiers, getting removed, or if your copay is changing. About 37% of plans change at least one generic’s tier each year.

Here’s what to do:

• Use the Medicare Plan Finder: Enter your exact medications. Filter by "generic only." See which plans cover them at $0 or $5 copays. KFF research shows users who do this save an average of $427 a year.
• Look for $0 deductible plans: Over half of stand-alone Part D plans in 2025 had $0 deductibles. If you take multiple generics, this can cut your costs in half.
• Ask for a coverage determination: If your drug isn’t on the formulary, request an exception. CMS data shows 83% of these requests get approved, especially for generics.
• Check for the new price comparison tool: Starting in 2026, all Part D plans must include a tool in their member portals that shows the lowest-cost generic alternative in your class. Use it.

What’s Coming Next

The changes aren’t over. In 2029, the Medicare Drug Price Negotiation Program will start requiring plans to cover negotiated prices for certain generics. Insulin glargine (generic Lantus) is already on the list. This could bring prices down even further.

Some experts are pushing for a new rule: if a plan covers any generic in a class, it must cover them all. That would end the "one generic only" problem. The Senate Finance Committee is already drafting legislation for this.

By 2027, analysts predict 95% of Medicare beneficiaries will have access to $0 copays for at least half of their commonly used generics. That’s up from 78% in 2024. The trend is clear: generics are becoming the default, affordable choice.

Real Stories, Real Savings

One user on Reddit, "SmartSenior2024," posted in February 2025: "My three generic heart medications cost me $0 under my Plan D’s Tier 1 coverage. I save over $300 monthly compared to what I paid before Medicare."

Another, "MedicareVeteran82," wasn’t as lucky: "My plan only covers one generic blood pressure med. When I switched to the one my doctor prescribed, I got hit with a $90 copay. I had to call for an exception-took three weeks to get approved."

These stories aren’t rare. They show how much can change based on a single formulary decision.

Bottom Line

Generic drugs are the most powerful tool you have to control your Part D costs. They’re safe, effective, and covered widely. But coverage isn’t automatic-you have to know your plan, check your formulary every year, and speak up if something’s missing. With the $2,100 out-of-pocket cap in place, you’re now protected from sky-high bills. Use that protection. Review your plan. Compare your options. And don’t assume anything stays the same.