How a formulary, tiering, step-therapy, or quantity-limit exception works
Checked against the current rules on September 23, 2026.
Four of the nine most common Part D denial reasons — a drug not on the formulary, a higher cost-sharing tier, a step-therapy requirement, and a quantity limit — are all governed by the same section, and all turn on the same evidence.
Source: 42 CFR Part 423, Subparts M & U — Part D Grievances, Coverage Determinations, Redeterminations, Reconsiderations, ALJ Hearings, Council Review, and Judicial Review.
A Part D plan must grant a formulary exception whenever it determines the requested drug is medically necessary, consistent with the prescriber's own supporting statement, and the drug would otherwise be covered but for being off-formulary.42 CFR 423.578
The same section explicitly treats step therapy, dosage/quantity restrictions, and a plan's own tiering structure as "formulary use" tools subject to this identical exceptions process — a step-therapy or quantity-limit denial is legally an exceptions request, not a separate category with its own weaker standard.42 CFR 423.578
For a tiering exception specifically, the prescriber's statement must say the preferred, lower-tier drug would not be as effective for this patient or would cause adverse effects — a plan cannot require more than that to grant it, though it may decline a tiering exception into the plan's own specialty tier.42 CFR 423.578
What this means for your appeal
The prescriber's own written or oral supporting statement is not optional paperwork — it is the legal trigger the plan is required to act on. A request without one is missing the one thing the rule actually asks for.
The plan's own clock to decide an exceptions request does not start until it receives that statement, and if 14 calendar days pass with none, the plan may decide (usually unfavorably) without it — getting the statement in fast is usually the single highest-leverage step in a Part D appeal.42 CFR 423.568
In practice, that means the single most useful thing a family can do before filing anything is call the prescriber's office directly, explain that the plan needs a written statement (not just a phone note in the chart) addressing medical necessity, and confirm the office has actually sent it to the plan rather than just written it into the patient's file. A statement that exists but was never transmitted doesn't start any clock.
Because a tiering, step-therapy, and quantity-limit denial all route through this identical exceptions machinery, the prescriber's statement should speak to whichever specific standard applies — why the preferred drug wouldn't work as well or would cause adverse effects for a tiering exception, or why the step-therapy drug already failed or is contraindicated for a step-therapy exception — rather than a generic "this drug is medically necessary" line that doesn't engage the actual test the plan has to apply.
Sources — last checked September 23, 2026
- 42 CFR 423.568as of September 23, 2026
- 42 CFR 423.578as of September 23, 2026
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By CaseWhy Appeals editorial. See how this content is produced. Not legal advice. Not affiliated with or endorsed by Medicare, CMS, or any health plan. A product of CaseWhy LLC.
