The short answer
Medicare Part D drug tiers are levels a plan sorts its covered drugs into, and a drug in a lower tier generally costs you less than one in a higher tier. Each plan divides its tiers its own way, so the same drug can sit differently in two plans.
Two plans can cover the same drug and charge you different amounts for it. Nothing about the drug is different. Each plan sorted its own list into levels, and yours landed where it landed.
What are Medicare Part D drug tiers?
Tiers are levels a plan puts its covered drugs into in order to lower costs. Each plan can divide its tiers in different ways. Generally a drug in a lower tier will cost you less than a drug in a higher tier, and that ordering is the only part Medicare fixes.
Notice what that sentence does not say. It does not say which drugs go where. It says lower costs less than higher, and leaves the sorting to the company.
A tier is a decision, not a property. This is our reading rather than a rule Medicare states. Three of its own facts point at it.
Each plan divides its tiers in different ways. The ladder Medicare publishes is labelled an example, with the warning printed beside it that your plan's tiers may be different. And a plan can change its drug list at any time.
Put together, the tier is a fact about your plan, not about your medicine. Those three facts are the government's. Reading them as one is ours.
What does each tier cost?
Medicare does not publish an amount for any tier, because plans set their own. What it publishes is an example of how a plan might build its ladder, with the ranking rather than the price, and it says outright that your plan's tiers may be different.
Here is that example, in Medicare's own wording.
| Tier in Medicare.gov's example | Copayment | What sits there |
|---|---|---|
| Tier 1 | Lowest | Most generic prescription drugs |
| Tier 2 | Medium | Preferred brand-name drugs |
| Tier 3 | Higher | Non-preferred brand-name drugs |
| Specialty tier | Highest | Very high-cost prescription drugs |
Two words in that table are worth separating, because your plan will use both. A copayment is a fixed amount you pay for a drug at the pharmacy. Coinsurance is a percentage you pay instead.
The difference matters most at the top of the ladder. Medicare states that your coinsurance may increase for a particular drug when the manufacturer raises the price, and a percentage of a large number moves further than a percentage of a small one.
Your plan's deductible and the yearly limit on what you pay out of pocket sit outside the tier system entirely. Both are covered in this publication's article on the Part D out-of-pocket cap.
Why is my drug on a high tier?
Your drug sits where your plan put it. Plans build their lists to cover a wide range of the drugs people with Medicare take, with a floor of at least two drugs in the most commonly prescribed categories and classes, and they choose which ones fill that floor.
So the honest answer to why is that the plan decided, inside rules that leave it room to decide.
The shelf can also move under you. Coinsurance can rise for a drug when the manufacturer raises the price. Your share can also rise when your plan adds a generic or biosimilar version to its list, moves the brand-name drug to a higher cost-sharing tier, and you keep taking the brand.
That second case is the one people meet without warning, and this publication's article on whether your drug is covered follows it through in full.
None of that requires anything of you. Which is exactly why it is worth knowing it can happen.
Can I request a tier exception?
Yes. A tiering exception is when a drug plan decides to charge a lower amount for a drug that is on its non-preferred tier. It does not move the drug. It changes what you pay for it while it stays where it is.
The route opens on a specific condition. If your drug is in a higher tier and your prescriber thinks you need that drug instead of a similar drug in a lower tier, you or your prescriber can ask the plan for a lower coinsurance or copayment on the higher-tier one.
Your doctor or other prescriber then has to provide a supporting statement explaining the medical reason. That statement is the substance of the request, and it comes from them rather than from you.
There is a wider version of the same idea. An exception can also mean the plan agreeing to cover a drug that is not on its list at all, or agreeing to waive one of its coverage rules.
How the request is filed, how long a decision takes, what expedited means, and what happens if it is refused are all set out in this publication's articles on Part D access restrictions.
What is a specialty tier?
The specialty tier is the top of the ladder in Medicare's published example. It carries the highest copayment of any tier and it holds very high-cost prescription drugs. It is the only rung named for what the drugs cost rather than for whether they are generic, preferred or non-preferred.
The name describes price, not category. A drug lands there because of what it costs rather than because of what it treats.
That is also where the copayment and coinsurance distinction bites hardest. A percentage of a very high-cost drug is a very different number from a fixed amount, and which of the two your plan uses on that tier is worth checking before you assume the tier alone tells you the cost.
The exception route above still exists at the top of the ladder. So does the requirement that your prescriber supply the medical reason.
How do generics fit in?
Generics sit at the bottom of Medicare's example ladder, on the lowest copayment tier, where most generic prescription drugs are placed. That position is the single biggest reason a plan's tier design works out cheaply for one person and expensively for another.
A generic drug is a copy of a brand-name drug. It matches the brand on dosage form, how it is taken, intended use, performance, quality, safety and strength, and its maker must prove to the Food and Drug Administration that its product works the same way. Both need that approval before anyone can prescribe them.
There is a parallel version for biological drugs, which are made from living sources such as animal cells, plant cells, bacteria or yeast. A biosimilar has to be highly similar to the original with no clinically meaningful difference in safety or effectiveness, and an interchangeable biosimilar can be substituted at the pharmacy without a new prescription, subject to your state's laws.
Medicare.gov offers one observation of its own here, and it is theirs rather than ours. If you take a lot of generic prescriptions, it suggests looking at plans whose tiers charge no copayment, or a low one, for generics.
What this means for you
A tier tells you what your plan decided about a drug. It does not tell you anything about the drug itself, which is why the same medicine can sit on different shelves in two plans and why yours can move shelves inside one plan.
Medicare fixes the ordering and nothing else. Lower costs less than higher. The ladder it publishes is an example, and it says so on the page.
Your bill turns on two things the ladder does not show: whether your plan charges a fixed amount or a percentage on the tier your drug sits on, and whether a change to the list has moved it.
If your prescriber believes you need the higher-tier drug rather than a similar cheaper one, the tiering exception exists, and it runs on their medical statement rather than on your argument.
For how the list itself works and when it can change, read this publication's article on whether your drug is covered. For filing an exception, read the articles on Part D access restrictions.
FAQ
Do all Medicare drug plans use the same tiers?
No. Medicare states that each plan can divide its tiers in different ways, and the ladder published on Medicare.gov is labelled an example with the warning that your plan's tiers may be different.
What Medicare fixes is the ordering rather than the contents: generally a drug in a lower tier will cost you less than a drug in a higher tier. Everything below that is the plan's own design. The practical effect is that comparing two plans by tier number tells you very little.
The same drug can be a low tier in one plan and a non-preferred brand in another, and the only list that answers the question for you is the one belonging to the plan you actually hold or are considering.
What is the difference between a copayment and coinsurance on a tier?
A copayment is a fixed amount you pay for a drug at the pharmacy. Coinsurance is a percentage you pay instead. Both appear in Medicare drug plans and a plan can use one on some tiers and the other elsewhere.
The distinction matters most on expensive drugs. A fixed amount does not move when a manufacturer raises a price, while a percentage does, which is why Medicare notes that your coinsurance may increase for a particular drug when the manufacturer raises the price.
On the specialty tier, which holds very high-cost drugs, the tier number alone does not tell you what you will pay, because the plan still chooses between a fixed amount and a percentage.
Can my plan move my drug to a different tier during the year?
Yes. Medicare states that plans can change their drug list at any time and that your plan must notify you of any changes to its drug list that affect drugs you are taking.
One case is named directly: your copayment or coinsurance may increase if you keep taking a brand-name drug or original biological product after your plan adds a generic or biosimilar version to the list and moves the brand-name drug to a higher cost-sharing tier.
In that situation the drug is still covered. It has moved to a more expensive place on the ladder, and continuing with the brand is what carries the higher cost. The notice rules that apply are set out in this publication's article on whether your drug is covered.
What does my prescriber have to do for a tiering exception?
Your doctor or other prescriber must provide a supporting statement explaining the medical reason for the exception. Medicare frames the tiering request around a specific condition: your drug is in a higher tier and your prescriber thinks you need that drug instead of a similar drug in a lower tier.
Either you or your prescriber can make the request, but the medical statement can only come from them. It is worth understanding that this is a clinical argument rather than a form to be completed correctly.
The wider form of an exception, where a plan agrees to cover a drug that is not on its list at all or to waive a coverage rule, uses the same requirement.
Is a specialty tier drug always expensive for me?
The specialty tier is defined by what the drugs cost rather than by what they treat: Medicare's example describes it as the highest copayment level, holding very high-cost prescription drugs. What you personally pay depends on your plan, because plans set their own amounts and choose whether to charge a fixed copayment or a percentage.
It also depends on where you are in your plan year, since your deductible and the yearly limit on out-of-pocket drug spending both change what a given prescription costs you. Those two are covered in this publication's article on the Part D out-of-pocket cap. The tiering exception route also remains open at the top of the ladder.
Why are generics on the lowest tier?
Medicare's published example places most generic prescription drugs on tier 1, the lowest copayment level. A generic is a copy of a brand-name drug that matches it on dosage form, how it is taken, intended use, performance characteristics, quality, safety and strength, and the maker must prove to the Food and Drug Administration that the product works the same way.
Because the same clinical result is available at a lower price, plans place them where they cost you least.
Medicare adds an observation of its own: if you take a lot of generic prescriptions, consider looking at plans with tiers that charge no copayment, or a low one, for generic prescriptions. In some cases no generic exists for your exact drug, though another generic may still work for you.
