What Is a Health Plan Formulary? Drug Tiers, Exceptions, and Denials Explained

A formulary is your health insurance plan's approved list of prescription medications. If your drug is on the formulary, it is covered — at a cost-sharing tier that determines your out-of-pocket cost. If it is not on the formulary, or if it is on a highly restricted tier, you may face a denial, a step therapy requirement, or an unaffordable cost share.

Understanding how formularies work puts you in a far better position to appeal denials, request exceptions, and get the medications your doctor has prescribed.

How Formulary Tiers Work

Most formularies organize drugs into four or five cost-sharing tiers:

• Tier 1 — Preferred generics: Lowest copay, typically $5–$15
• Tier 2 — Non-preferred generics or preferred brand-name drugs: Moderate copay
• Tier 3 — Non-preferred brand-name drugs: Higher copay or coinsurance
• Tier 4 — Specialty drugs: Highest cost-share, sometimes percentage-based (e.g., 30–50%)
• Tier 5 (some plans) — Excluded drugs: Not covered at any tier

The higher the tier, the more you pay. Specialty drug tiers are often where the most significant cost barriers arise, particularly for biologics, cancer drugs, and treatments for chronic conditions like multiple sclerosis or rheumatoid arthritis.

Non-Formulary Drugs

A drug is "non-formulary" if it does not appear on your plan's formulary at all. Non-formulary drugs are typically not covered unless you obtain a formulary exception (see below). This is a common source of claim denials when physicians prescribe medications outside the standard coverage list.

Prior Authorization Denied: How to Appeal" class="auto-link">Prior Authorization and Formulary Access

Many formulary drugs — particularly specialty and brand-name medications — require prior authorization (PA) before your insurer will approve coverage. PA is a separate process from the formulary itself: even if a drug is on the formulary, you may still need to prove medical necessity before coverage kicks in.

If your prior authorization was denied, that denial is separately appealable from a formulary exclusion denial.

Step Therapy: The "Fail-First" Requirement

Step therapy policies require you to try one or more lower-cost, typically generic, alternatives before your plan will cover the drug your doctor originally prescribed. For example: your doctor prescribes a brand-name biologic for Crohn's disease, but your plan requires you to first try (and fail on) two generic alternatives.

Step therapy is legal in most states, but many states have enacted exceptions — allowing your doctor to bypass step therapy when:

• The required alternative is contraindicated
• You have already tried and failed the alternative drug
• The delay would cause irreversible harm
• The required drug is not clinically appropriate for your condition

If your state has a step therapy exception law, document the clinical reason for exception and submit a formal request.

How to Request a Formulary Exception

A formulary exception asks your insurer to cover a non-formulary drug (or a formulary drug at a lower cost-sharing tier) based on medical necessity. To request an exception:

1. Have your physician complete the insurer's formulary exception form and submit a letter of medical necessity explaining why the prescribed drug is necessary and why formulary alternatives are not appropriate.
2. Include supporting clinical documentation — prior treatment history, failed trials of alternatives, relevant diagnosis codes, and peer-reviewed literature if applicable.
3. Submit the exception request through your insurer's pharmacy benefit manager (PBM) or directly to your insurer.
4. Urgent or expedited requests must be processed within 24–72 hours under federal rules; standard requests within 72 hours for Part D and within plan-specified timelines for commercial plans.

Appealing a Formulary Denial

If your exception request or prior authorization for a formulary drug is denied, you have the right to appeal. The denial notice must include:

• The specific reason for denial
• The criteria applied
• Your appeal rights and deadlines

Under the ACA, you can appeal internally and then request External Independent Review: Complete Guide" class="auto-link">external review from an IROs) Explained" class="auto-link">independent review organization (IRO). The external reviewer is not bound by your insurer's formulary decisions — they apply medical necessity standards.

Formulary Changes Mid-Year

For ACA marketplace and employer plans, your insurer generally cannot remove a drug from the formulary mid-year if you are currently using it and remain enrolled. If your insurer removes your medication from formulary between enrollment periods, you may have grounds to file a complaint with your state insurance commissioner or CMS.

Exception: plans may move a drug to a different tier or impose new restrictions if a generic equivalent becomes available.

Drug Cost Caps and Insulin Protections

Several states have capped out-of-pocket insulin costs. The Inflation Reduction Act (2022) capped Medicare Part D insulin costs at $35/month. Some ACA marketplace plans now also cap insulin costs. If you are being charged more than the applicable cap, file a complaint immediately.

Fight Back With ClaimBack

If your prescription was denied because it is not on formulary, requires step therapy you cannot safely follow, or was placed on an unaffordable cost-sharing tier, you have the right to appeal and request an exception. ClaimBack helps you build the documentation needed to win.

Start your appeal at ClaimBack

Related Reading

• What Is Prior Authorization?
• What Is Step Therapy?
• What Is Medical Necessity?