Step therapy requires you to try a plan-preferred medication before the plan covers another drug. Your prescriber can request an exception when the required drug may be ineffective or harmful.
Step therapy means your Part D plan requires you to try another covered drug before it pays for the one prescribed. It is a type of prior authorization, or advance approval. The first drug may be a lower-cost generic, a drug the plan prefers, or a biosimilar, which is a similar alternative to a biologic medicine.
The first drug must be a reasonable treatment option, but it may not be right for every patient.
How Do You Know Step Therapy Applies?
The plan’s list of covered drugs, called a formulary, or its online drug search may mark the medication with “ST.” The pharmacy may also receive a rejection when it submits the claim.
Ask the plan:
- Which drug must be tried first?
- How long must you try it?
- What records show that you tried the drug before or had a harmful reaction?
- Does the plan already have your treatment history?
How Do You Request an Exception?
You or your prescriber can request a step-therapy exception. The prescriber must provide the plan with a supporting statement explaining that the required drug:
- Is likely to be less effective
- Could cause harmful effects
- Has already been tried without success
- Is medically inappropriate for another documented reason
If the plan approves the exception, it covers the requested drug at the price set by its drug tier and payment rules.
If it denies the request, you can appeal. Ask for an expedited, or faster, decision when the normal wait could seriously harm your health.
Medicare's drug-plan rules explain the exception process.
If you previously tried the preferred medicine and stopped because it did not work or caused a harmful reaction, give the prescriber the drug name, dates, dose, and reason for stopping. The prescriber can send that history to the plan’s office that handles coverage decisions to support an exception; it does not guarantee approval. Ask the plan to confirm receipt, and see the standard and expedited decision timelines. Approval lets you skip the required first drug. It does not by itself put your prescription in a lower-cost tier or remove your share of the cost.
Medicare policy sources last checked: October 8, 2026.