What is Formulary and How Health Plan Drug Lists and Tiers Work
Last updated 07/23/2026 by
Ante Mazalin
Edited by
Andrew Latham
Summary:
A formulary is the list of prescription drugs that a health insurance plan agrees to cover. Plans sort those drugs into pricing tiers and attach rules that affect what you pay and how you get approval.
- Tiers: Groupings that set your share of the cost, from low-cost generics to high-cost specialty drugs.
- Coverage rules: Requirements like prior authorization or step therapy before a drug is covered.
- Updates: The list can change during the year, moving or dropping drugs.
Your formulary decides whether a prescription costs a few dollars or several hundred. Knowing how it is organized helps you avoid surprise bills at the pharmacy counter.
What a formulary is
A formulary is a health plan’s official list of covered medications, built by a committee of pharmacists and doctors. Drugs on the list are covered, and drugs left off it usually are not.
Plans use the formulary to steer members toward effective, lower-cost options. A generic on the list can cost a fraction of an equivalent brand-name drug that sits on a higher tier or off the list entirely.
The list is not fixed. A plan can add drugs, drop them, or move them to a different tier during the plan year, though it must usually notify affected members first.
How drug tiers work
Most formularies group drugs into three to five tiers. A lower tier means a lower share of the cost for you, whether that share is a flat copay or a percentage.
| Tier | Typical drugs | Your cost |
|---|---|---|
| Tier 1 | Preferred generics | Lowest copay |
| Tier 2 | Non-preferred generics | Low copay |
| Tier 3 | Preferred brand-name drugs | Moderate copay |
| Tier 4 | Non-preferred brand-name drugs | Higher copay |
| Tier 5 | Specialty drugs | Highest, often coinsurance |
Specialty drugs on the top tier often use coinsurance instead of a flat copay, meaning you pay a percentage of a high price. Those costs count toward your out-of-pocket maximum.
Formulary rules that affect coverage
Even when a drug is on the formulary, the plan may attach conditions before it pays. According to Medicare.gov, three rules are the most common.
- Prior authorization: Your plan must approve the drug before you fill it, often to confirm it is medically necessary.
- Step therapy: You must try a lower-cost drug first, and only if it fails will the plan cover the pricier option.
- Quantity limits: The plan caps how much of a drug it covers over a set period.
Starting in 2026, new federal rules require electronic prior authorization with decision deadlines of 72 hours to seven days, according to guidance from the Centers for Medicare and Medicaid Services.
Pro Tip
Before you enroll in a plan, search its formulary for every drug you take by name and dose. A single specialty medication on a high tier can cost more out of pocket than the difference in annual premiums between two plans, so the formulary often matters more than the monthly price.
Checking coverage takes only a few minutes and can prevent a denied claim later. The steps are the same across most plans.
How to check if your drug is covered
- Find the plan’s drug list: Look for the current-year formulary on the insurer’s website or member portal.
- Search by drug name and dose: Coverage can differ by strength and form, so match your exact prescription.
- Note the tier: The tier tells you roughly what you will pay.
- Check for restrictions: Look for flags marking prior authorization, step therapy, or quantity limits.
- Ask about alternatives: If your drug sits on a high tier, your doctor may be able to prescribe a lower-tier option.
If your drug is not covered or sits on a costly tier, you still have options beyond simply paying more.
What to do if your drug is not on the formulary
A drug left off the formulary is not automatically off-limits, but you will need to act. The fastest route is usually switching to a covered alternative that treats the same condition.
You can also request a formulary exception, where your doctor submits evidence that the drug is medically necessary. If the plan denies it, you have the right to appeal that decision.
Related reading on health plan costs
- Deductible explains the amount you pay before coverage, which can apply to drug costs.
- High-deductible health plan shows how drug spending works when your deductible is large.
- EPO insurance covers a plan type that pairs a formulary with a limited provider network.
Frequently asked questions
What does it mean when a drug is on the formulary?
It means the health plan agrees to cover that drug, though your cost depends on its tier. Drugs not on the formulary are usually not covered unless you get an exception.
Why did my drug move to a higher tier?
Plans update formularies during the year and can move drugs based on cost, new alternatives, or contract changes with manufacturers. The plan must generally notify you before the change takes effect.
What is a formulary exception?
It is a formal request for your plan to cover a drug that is not on the list or to lower its tier. Your doctor provides medical justification, and the plan must respond within set deadlines.
Do all plans use the same formulary?
No. Each insurer builds its own formulary, so the same drug can be a low-cost generic on one plan and an expensive non-preferred drug on another.
Key takeaways
- A formulary is the list of prescription drugs your health plan covers.
- Drugs are sorted into tiers, with lower tiers costing you less than higher ones.
- Coverage rules like prior authorization, step therapy, and quantity limits can apply even to listed drugs.
- Formularies change during the year, so a covered drug can move tiers or drop off.
- If a drug is not covered, you can switch to an alternative or request a formulary exception and appeal a denial.
Prescription coverage varies widely from one plan to the next, and it can outweigh the monthly premium in real cost. You can compare health insurance plans to find a formulary that covers the drugs you actually take.
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