Blog / Part D

What is prior authorization and step therapy for my medication?

Two ways a plan controls costs before covering a drug. Both are appealable, and both are worth checking before you enroll.

Updated August 17, 2026 · 3 min read

Your drug can be on the formulary and still not get filled at the counter. Two restrictions cause this, and neither is a denial.

Prior authorization

The plan requires approval before it will cover the drug. Your doctor submits clinical information showing why you need it.

Plans have deadlines to respond. Standard requests get a decision within a set number of days, and expedited requests, used when waiting could seriously harm your health, are much faster.

Most requests are approved. The cost is the delay and the paperwork, which lands on your doctor's staff and on you.

Step therapy

The plan requires you to try a lower cost drug first. Only if it does not work adequately will the plan cover the one your doctor originally prescribed.

Quantity limits

A cap on how much the plan covers per fill or per period, usually based on the manufacturer's recommended dosing. If your prescription exceeds it, your doctor requests an exception with clinical justification.

How to get through it

1. Ask the pharmacy exactly which restriction applies. They can see it in the system.
2. Call your prescriber's office and tell them specifically which restriction and which plan. Most offices handle these regularly.
3. Ask about an expedited request if waiting would harm you.
4. If you have already tried and failed on the step therapy alternative, say so and provide the history. That usually resolves it.
5. If denied, appeal. There are multiple levels and denials are overturned reasonably often.

The transition supply

When you join a new plan or a formulary changes in January, the plan must generally provide a temporary supply of a drug you were already taking, usually a one month fill within the first 90 days.

That exists so you are not left without medication while an authorization is sorted out. Use it, and start the authorization immediately rather than waiting until the temporary supply runs out.

Check for restrictions before you enroll

The Plan Finder at Medicare.gov flags prior authorization, step therapy and quantity limits on each drug for each plan.

A plan that is cheapest on paper but applies step therapy to a drug you are stable on is not the cheapest plan. Check the flags, not just the totals. See how to compare properly.

Advantage plans use it on the medical side too

Prior authorization is not limited to drugs. Medicare Advantage plans commonly require it for imaging, skilled nursing stays and some procedures. If you are choosing a plan, it is fair to ask how extensively it uses prior authorization and how quickly it typically decides.

See the honest downsides of Advantage plans.