Prescription benefits are one of the easiest parts of health insurance to misunderstand because the drug name alone does not tell you what you will pay. Two plans can both “cover” the same medicine while producing very different out-of-pocket costs because of tier placement, deductibles, pharmacy networks or utilization-management rules.
HealthCare.gov advises Marketplace enrollees to review the plan formulary, Summary of Benefits and Coverage and insurer materials to confirm which prescriptions are covered. For Medicare Part D, CMS separately regulates formularies, coverage determinations and exceptions. The details differ by type of health coverage, so consumers should not assume Marketplace and Medicare rules are identical.
What is a formulary?
A formulary is a plan’s approved drug list. It usually organizes covered drugs into cost-sharing levels or tiers. A plan can also attach management rules to a particular drug, such as prior authorization, step therapy or quantity limits.
| Formulary feature | What it can mean | What to check |
|---|---|---|
| Tier | Different copay or coinsurance level | Your exact cost at the preferred pharmacy |
| Prior authorization | Plan approval may be required before coverage | Who submits the request and what clinical criteria apply |
| Step therapy | You may need to try another covered drug first | How to request an exception if the first-step drug is inappropriate |
| Quantity limit | Coverage may limit doses or units in a period | Whether a higher quantity can be approved |
| Pharmacy network | Cost can depend on where the prescription is filled | Preferred, standard, specialty and mail-order rules |
Drug tiers are not standardized across every plan
Many plans use multiple tiers, but the number and labels vary. A common structure may separate generics, preferred brands, non-preferred brands and specialty drugs. That structure is only an example; the actual plan documents control.
More important than the tier name is the cost formula. One tier may use a fixed copayment while another uses coinsurance based on the drug’s allowed price. A medicine can therefore become much more expensive after a plan change even when it remains “covered.”
Prior authorization, step therapy and quantity limits
Prior authorization means the plan wants specified clinical information or approval before paying under the prescription benefit. Step therapy generally requires trying one or more preferred alternatives before moving to another drug. Quantity limits restrict the covered number of doses or units over a period.
These controls are not the same as a permanent denial. Depending on the plan and coverage type, a prescriber may be able to request an exception when the required alternative would be ineffective, harmful or otherwise medically inappropriate. CMS explains that Medicare Part D formulary exception requests can seek coverage for a non-formulary drug or a waiver of utilization-management requirements such as step therapy, prior authorization or a quantity limit.
Marketplace coverage: what HealthCare.gov tells consumers to do
HealthCare.gov recommends checking the insurer’s drug list, the Summary of Benefits and Coverage and the plan’s own materials. It also advises consumers to verify whether their regular pharmacy is in network. If a Marketplace plan will not cover a needed drug, the federal Marketplace guidance describes an exception process and a right to appeal an adverse decision.
This is a good reason to review prescriptions before changing plans, not after enrollment. A lower monthly premium can be offset by higher drug costs or narrower pharmacy access.
Medicare Part D: a separate framework
Medicare Part D has its own formulary and coverage-determination rules. CMS defines a tiering exception as a request to receive a non-preferred drug at the cost-sharing terms of a preferred tier, when allowed, and a formulary exception as a request for a non-formulary drug or relief from certain utilization-management restrictions. These rules should not be casually applied to employer coverage or Marketplace plans.
A practical pre-enrollment medication audit
- Write down the exact drug name, dose, form and frequency for every ongoing prescription.
- Search each drug in the plan’s current formulary.
- Record the tier and whether prior authorization, step therapy or a quantity limit applies.
- Check whether your pharmacy is preferred or merely in network.
- Estimate annual cost, not only the first refill.
- Check whether specialty drugs must be filled through a designated specialty pharmacy.
- Ask how the plan handles exceptions and urgent requests.
Use the plan’s Summary of Benefits and Coverage as a starting point, then go deeper into the formulary. If a service or drug requires advance approval, our prior authorization guide explains the broader process. If a claim or coverage request is denied, review internal appeals and external review.
Scenario: the same drug, three very different outcomes
Imagine a patient takes a specialty medication that costs thousands of dollars per month before insurance discounts. Plan A covers it on a specialty tier with coinsurance. Plan B requires step therapy before approving it. Plan C excludes it from the standard formulary but offers an exception process. All three plans can accurately say they have prescription benefits, yet the practical patient experience is completely different.
What to save if you request an exception
- The denial or pharmacy rejection message.
- The formulary page showing the drug or restriction.
- Clinical documentation from the prescriber.
- Records of drugs already tried and adverse effects.
- Dates, names and confirmation numbers for calls or submissions.
- Any written decision and appeal deadline.
Frequently asked questions
If a drug is on the formulary, is it automatically cheap?
No. Tier placement, deductibles, copays, coinsurance and pharmacy network rules can materially affect cost.
Is step therapy the same as prior authorization?
No. They are different utilization-management tools. A drug can be subject to one, both or neither.
Can I ask for a non-formulary drug to be covered?
Many plans have exception or appeal procedures, but the rules depend on the type of plan. HealthCare.gov and CMS provide separate guidance for Marketplace coverage and Medicare Part D.
Can the formulary change?
Plans can make formulary changes subject to applicable rules. Review current plan notices and the live formulary rather than relying on an old copy.
Sources and further reading
Reviewed October 6, 2026. Formularies and exception rights differ by plan type. Verify the current plan document, formulary and applicable appeal rules.
