What is prior authorization?

Benefily Team17 July 202610 min read

A prescriber reviewing a signed prescription slip across a desk before submitting it for prior authorization

Your doctor prescribes a drug. The pharmacy says it needs prior authorization first, and now you're stuck waiting, with no idea how long that takes or why it's happening at all. This guide explains what prior authorization actually is, how it works for Medicare Part D drug plans specifically, and the exact deadlines a plan must meet once your prescriber files the request. It draws on Medicare's own coverage-determination rules and the newest published data on how often requests are approved, refused, and overturned on appeal, so you know what's normal and what's worth challenging.

Key takeaways

Prior authorization is a plan's check that a drug is medically necessary and meets its coverage rules before it will pay for it.
For Medicare Part D, plans must decide standard requests within 72 hours and expedited requests within 24 hours.
It's a different mechanism from step therapy (try a cheaper drug first) and a formulary exception (asking for a drug that isn't on the list at all).
In 2024, Medicare Advantage insurers processed nearly 53 million prior authorization requests and denied around 8% of them.
A denial isn't the end of the road. It can be appealed, and most appeals that are actually filed get overturned.
If a plan misses its own deadline, that counts as a denial you can appeal straight away.

What prior authorization actually means

Prior authorization is a rule a health plan attaches to certain drugs: before it will pay its share of the cost, your prescriber has to show the plan why you need that specific medicine. It sits between the prescription being written and the plan agreeing to cover it, which is why some people call it pre authorization or a pre-approval requirement instead. The terms mean the same thing.

It's worth being precise about what it doesn't do. Prior authorization doesn't stop you collecting the drug, and it isn't a medical judgement about whether the prescription is appropriate. It's a payment gate. Your pharmacist can still fill the prescription today if you (or someone else) pays the full cash price; what's missing is the plan's contribution until the paperwork clears.

How it works for a Medicare Part D drug

Every Part D plan files a formulary with Medicare: the list of drugs it covers, and the rules attached to each one. A prior authorization flag is one of three restriction types that can sit on a formulary row, alongside step therapy and quantity limits. In practice, the process runs in a fixed sequence:

Your prescriber writes the prescription and sends it to the pharmacy as normal.
The pharmacy's system checks the drug against your plan's formulary and flags the prior authorization requirement at the point of sale.
Your prescriber (not you, and not the pharmacist) submits a request to the plan, usually including your diagnosis and why alternative drugs aren't suitable.
The plan makes what Medicare calls a coverage determination — a formal yes, no, or request for more information.
If approved, the pharmacy can bill the plan and you pay only your normal copay. If refused, you receive a written notice explaining why, and how to appeal.

Standard vs expedited: the deadlines that apply

This is the part most explanations skip, and it's the one that matters most if you're the one waiting. Medicare sets a hard clock on how long a Part D plan can sit on a coverage determination, and the clock starts the moment your prescriber's office submits the request, not when you first asked about it.

Request type	Decision deadline	When it applies
Standard	72 hours	Routine requests, where waiting won't seriously affect your health
Expedited	24 hours	Your prescriber states, or the plan agrees, that waiting could seriously jeopardise your health or ability to function

Medicare Part D coverage determination deadlines, standard vs expedited (42 CFR 423.568 and 423.572).

If a plan misses either deadline, it doesn't get more time by default. A missed deadline is treated as an automatic denial, which means you can move straight to an appeal (a redetermination) rather than waiting indefinitely for an answer that never comes.

Prior authorization vs step therapy vs a formulary exception

These three terms get used almost interchangeably, but a plan applies each one for a different reason, and the fix is different too.

Mechanism	What triggers it	What resolves it
Prior authorization	The drug carries a PA flag on the formulary, regardless of what you've tried before	Your prescriber submits clinical justification for a coverage determination
Step therapy	The plan requires you to try (and fail) a cheaper, similarly effective drug first	Proof you've already tried the preferred drug, or a clinical reason you can't
Formulary exception	The drug isn't on the plan's formulary at all	A tier or formulary exception request showing medical necessity for that specific product

Three formulary restrictions, and what actually resolves each one.

Why do plans require it in the first place?

Cost is the obvious driver: prior authorization is concentrated on expensive brand-name drugs, drugs with cheaper alternatives, and drugs frequently prescribed off-label. But it isn't only about cost. Plans also use it to catch genuine safety issues, such as a dose or combination that's unusual for your diagnosis, before the drug reaches you rather than after.

What happens if your request is denied

“Nearly all Medicare Advantage enrollees (99%) are in plans that require prior authorization for some services. In 2024, nearly 53 million prior authorization requests were submitted to Medicare Advantage insurers, with insurers denying 4.1 million, or nearly 8% of those requests.”
— KFF, Medicare Advantage in 2026

A denial notice has to tell you why you were refused and exactly how to challenge it. The first step is a redetermination, requested from the plan itself within 60 days of the denial notice. If that's unsuccessful, an independent reviewer outside the plan looks at it next, and the case can climb further from there through an administrative law judge if the amount at stake is large enough.

It's genuinely worth doing. Appeal rates are low across Medicare Advantage overall, but the outcomes for people who do appeal are strongly in their favour, which suggests a good number of denials don't hold up once someone actually pushes back.

Common mistakes

Assuming a drug missing from the formulary means no authorization is needed. It almost always means the opposite: the drug isn't covered at all.
Letting the appeal window lapse. A standard redetermination must be requested within 60 days of the denial notice.
Sending the appeal to the pharmacy rather than the plan. The pharmacist can't overturn a coverage decision; only the plan (and then an independent reviewer) can.
Assuming a denial for one strength or dose applies to the whole brand, when the formulary row for a different strength of the same drug may carry no restriction at all.

Frequently asked questions

How long does prior authorization take for Medicare Part D?

A standard request must be decided within 72 hours of your prescriber submitting it. An expedited request, used when waiting could seriously harm your health, must be decided within 24 hours.

What's the difference between prior authorization and a formulary exception?

Prior authorization applies to a drug that is on the formulary but flagged for review. A formulary exception applies when the drug isn't on the formulary at all, and you're asking the plan to cover it anyway.

Can a pharmacist approve or override a prior authorization requirement?

No. A pharmacist can tell you a drug needs prior authorization and can bill the plan once it's approved, but only your prescriber can submit the request, and only the plan can approve it.

Does a drug missing from the formulary mean I don't need prior authorization?

No, and this is one of the most common misunderstandings. A drug absent from a formulary is not covered at all, which is a worse position than needing authorization. It's never a sign that no approval is required.

What should I do if my prior authorization request is denied?

Read the denial notice for the specific reason, then ask your prescriber to file a redetermination request with the plan within 60 days. Include any additional clinical detail the notice asked for, since incomplete redeterminations are a common reason appeals stall.

Related on Benefily

Sources

Administrative information only. Benefily reports what a payer has published in its own prior-authorization policy as of the effective date shown. It is not medical advice, not a coverage or payment guarantee, and not an authorization. Requirements vary by plan, place of service and member benefits — always verify with the payer before rendering service.