What Is a Formulary in Health Insurance?

Your doctor writes a prescription, you take it to the pharmacy, and the pharmacist tells you it will cost $400 because it is not on your plan’s formulary. If you have never heard the term, you are not alone. A formulary is the list of prescription drugs your health insurance plan agrees to cover – and understanding how it works can save you hundreds or even thousands of dollars a year. This article is general education, not medical or insurance advice, and the dollar figures below are illustrative, so always confirm the details against your own plan. For more on how healthcare costs add up, visit our healthcare costs guide.

What Is a Formulary? A Plain-Language Answer

What is a formulary in practical terms? HealthCare.gov defines it plainly as “a list of prescription drugs covered by a prescription drug plan or another insurance plan offering prescription drug benefits,” also called a drug list. In other words, it is a curated list maintained by your insurance company or pharmacy benefit manager (PBM) that determines which medications are covered, how much you pay for each one, and whether you need extra approval before the plan will pay. Every Medicare Part D plan, ACA marketplace plan, Medicaid program, and employer-sponsored plan maintains its own formulary.

Formularies are developed by a committee of pharmacists, physicians, and sometimes patient advocates known as a Pharmacy and Therapeutics (P&T) committee. This committee evaluates clinical evidence, FDA approvals, safety data, and cost-effectiveness to decide which drugs make the list and at which tier. Importantly, FDA approval of a drug does not guarantee formulary inclusion. The Centers for Medicare & Medicaid Services (CMS) requires that Medicare Part D formularies cover at least two drugs in most therapeutic categories. (If you want a deeper dive into the mechanics, tier structures, and PBM influence, see our companion explainer on the formulary definition.)

Understanding Formulary Tiers

Most formularies organize drugs into tiers, with each tier carrying a different cost-sharing amount. While the exact structure varies by plan, a typical setup includes four to six tiers. The examples below are common patterns, not fixed rules – your plan’s exact tiers and amounts are in its plan documents.

Tier 1: Preferred Generic Drugs

These are usually the least expensive options, often costing only a few dollars per prescription. Generic drugs contain the same active ingredient as their brand-name counterparts and are approved by the FDA as safe and effective equivalents.

Tier 2: Non-Preferred Generics or Preferred Brand-Name Drugs

Copays here are typically moderate. A brand-name drug might land on Tier 2 if no generic alternative exists or if the manufacturer has negotiated a favorable rebate with the PBM.

Tier 3: Non-Preferred Brand-Name Drugs

Expect higher copays or coinsurance. These medications generally have alternatives on lower tiers that the plan considers clinically comparable.

Tier 4 and Above: Specialty Drugs

Specialty medications – used for conditions like rheumatoid arthritis, multiple sclerosis, or cancer – can cost hundreds or thousands of dollars per fill, even with insurance. Many plans apply coinsurance (a percentage of the drug’s price) rather than a flat copay for specialty drugs, which means your cost rises with the price of the medication. Specialty drugs make up a small share of prescriptions but account for a large and growing share of total drug spending, according to pharmacy and health-policy analyses; verify current figures, as they shift year to year.

What Happens When Your Drug Is Not on the Formulary

If your medication is excluded from the formulary entirely, your plan generally will not cover it, and you would pay the full negotiated or retail price at the pharmacy. However, you have several options before accepting that cost.

First, ask your doctor about therapeutic alternatives that are on the formulary. A different medication in the same drug class may work just as well for you. Second, your prescriber can submit a formulary exception request – a formal request arguing that the non-formulary drug is medically necessary for your situation. For Medicare Part D, Medicare.gov and CMS rules require plans to decide a standard exception request within 72 hours and an expedited (fast) request within 24 hours; these timeframes can change, so confirm the current rules. Third, check whether the drug manufacturer offers a patient assistance program. Many pharmaceutical companies provide medications at reduced cost, or free, for patients who meet income criteria.

Prior Authorization, Step Therapy, and Quantity Limits

Even drugs on the formulary may come with restrictions, collectively called utilization management. The three most common are prior authorization, step therapy, and quantity limits.

Prior authorization (PA) requires your doctor to get approval from the insurance company before the plan will cover a specific drug. The process involves submitting clinical documentation explaining why the medication is needed, and timelines vary by plan and request type. PA is especially common for expensive brand-name and specialty drugs. Our guide to what prior authorization means walks through the full process and the 2026-2027 federal reforms.

Step therapy, sometimes called “fail first,” requires you to try less expensive medications before the plan will cover a more costly one. For example, your insurer might require you to try one or more generic options before approving a newer brand-name drug. If a required first-line drug fails or causes side effects, the plan generally then approves the originally prescribed medication after documentation from your prescriber. While step therapy can lower costs, it can also delay effective treatment – a concern that has prompted many states to pass step-therapy reform laws.

Quantity limits cap how many doses or units the plan will cover per fill or per period. These are usually aligned with FDA-approved dosing but can sometimes conflict with your prescriber’s judgment, in which case an exception can be requested.

Formulary Changes: What to Watch For

A formulary is not frozen for the year. Insurance companies can and do change their formularies – adding drugs, removing drugs, moving a drug to a higher tier, or adding restrictions – for example when a generic launches, when new safety information emerges, or when a drug is withdrawn from the market. Consumer protections apply: plans generally must notify affected members before certain negative changes take effect, and Medicare Part D plans have specific advance-notice and transition-supply rules so you are not suddenly left without medication.

This matters most during open enrollment. Before renewing your plan or choosing a new one, check the formulary to confirm that all your current medications are still covered and on the same tier. Moving from a lower tier to a higher one can add hundreds of dollars a year in out-of-pocket costs. If you receive a mid-year change notice, read it promptly and talk with your prescriber about your options before your next refill.

Medicare Part D and Formulary Rules

Medicare Part D formularies are subject to stricter federal regulations than commercial plans. CMS requires that Part D plans cover at least two drugs in each therapeutic category and class, with broader requirements for six protected classes: anticonvulsants, antidepressants, antineoplastics (cancer drugs), antipsychotics, antiretrovirals (HIV drugs), and immunosuppressants for transplant rejection. For these classes, plans must cover “all or substantially all” drugs.

Part D plans also follow a defined coverage structure. Historically this included a deductible phase, an initial coverage phase, a coverage gap (the so-called “donut hole”), and catastrophic coverage. The Inflation Reduction Act reshaped this: it capped annual out-of-pocket prescription drug costs for Medicare beneficiaries at $2,000 beginning in 2025, eliminated the coverage-gap phase, and ended cost-sharing after the cap is reached. That cap is indexed and rises modestly in later years, so verify the current-year figure at Medicare.gov. These changes significantly affect how formulary tier placement impacts total annual drug spending for Medicare enrollees. For a Medicare-specific walkthrough, see our Medicare formulary guide.

How to Find Your Plan’s Formulary

Every insurer is required to make its formulary publicly available. You can usually find it by logging into your insurance account online and navigating to the prescription drug section, or by checking your PBM’s website (for example, CVS Caremark, Express Scripts, or OptumRx). Our overview of PBM services explains the role these companies play. Medicare Part D formularies are searchable on Medicare.gov’s Plan Finder tool, and marketplace plans list their formularies on the plan details page at HealthCare.gov. State Medicaid programs publish a Preferred Drug List (PDL) on the state Medicaid agency’s website.

When reviewing a formulary, pay attention to more than just whether your drug is listed. Note the tier, any prior authorization requirements, quantity limits, step-therapy rules, and whether the plan requires you to use a mail-order pharmacy for maintenance medications. For plain-language background on medicines and coverage, MedlinePlus from the National Library of Medicine is a reliable, non-commercial resource.

Frequently Asked Questions

Can my doctor override the formulary?

Your doctor can request a formulary exception by submitting clinical documentation to your insurance company. If approved, the plan covers the non-formulary drug, sometimes at a higher cost-sharing level. Approval is not guaranteed, but thorough medical records supporting medical necessity improve your chances.

Are all generic drugs on the formulary?

Not necessarily. While most plans cover a wide range of generics, some may exclude certain generic drugs if multiple alternatives exist in the same class. Always verify coverage before assuming a generic will be inexpensive.

Does the formulary apply to my deductible?

Often, yes. Before you have met any drug deductible, you may pay the full negotiated price for formulary drugs rather than just a copay. Once you meet the deductible, your tier-based copay or coinsurance kicks in. Some plans exempt Tier 1 generics from the deductible – check your plan documents.

What is a closed formulary vs an open formulary?

A closed formulary only covers drugs explicitly listed – anything not on the list generally gets no coverage unless you obtain an exception. An open formulary covers a broad range of FDA-approved medications but charges significantly more for drugs not on the preferred list. Many employer and marketplace plans use a closed or semi-closed structure.

Is a formulary the same as a drug list?

In everyday use, yes. HealthCare.gov itself uses both terms. “Formulary” implies a tiered, structured system with cost-sharing rules, while “drug list” is the more informal label, but they refer to the same document.

Formulary Tips for Open Enrollment

The annual open enrollment period is the best time to align your drug coverage with your actual medication needs. Before selecting or renewing a plan, list every prescription you currently take, including dosage and frequency. Then check each medication against the formulary of any plan you are considering. Pay attention to tier placement, prior authorization requirements, step therapy, and quantity limits. A plan with a lower monthly premium can end up costing you far more if it places your maintenance medication on a higher tier. Tools like the Medicare Plan Finder can help you estimate annual drug costs under different plans, and reputable price-comparison sites can give you a sense of cash prices – though estimates vary and should be verified.

The Bottom Line

Your plan’s formulary directly determines how much you spend on medications every month. Before filling any new prescription, check whether the drug is on your formulary and which tier it occupies. If it is not covered or sits on an expensive tier, talk to your doctor about alternatives, request an exception, or explore manufacturer assistance programs. Reviewing your formulary during open enrollment is equally important – a plan with lower premiums may cost you more overall if your medications are on higher tiers. The 15 minutes you spend reviewing the drug list can easily translate into meaningful annual savings. For more on how coverage fits into the wider system, see our healthcare policy guide.

Sources

• HealthCare.gov — Glossary definition of a formulary / drug list
• Centers for Medicare & Medicaid Services (CMS) — Medicare Part D coverage, formulary requirements, coverage determinations, exceptions, and appeals timelines
• Medicare.gov — Plan Finder and drug-coverage rules
• MedlinePlus (U.S. National Library of Medicine) — managing your medicines and prescription coverage