How to Write a Letter of Medical Necessity in 2026 (7-Part Template)
Step-by-step LMN template with the 7 sections payers look for, payer-specific language that wins, and the 6 mistakes that cause 80% of denials.
What Is a Letter of Medical Necessity?
A Letter of Medical Necessity (LMN) is a clinician-authored document that justifies why a specific drug, device, or service is medically required for a particular patient. Payers request LMNs when a prescription falls outside of formulary, requires step therapy override, or has been initially denied at prior authorization.
A well-written LMN combines patient-specific clinical facts with citations to peer-reviewed evidence and payer policy language. The goal is to make the reviewer's decision easy: approve.
The 7 Components of a Winning LMN
Every effective LMN contains the same core elements. Missing any one of them gives the reviewer a reason to deny.
- ✓ Patient identification (name, DOB, member ID, plan)
- ✓ Diagnosis with ICD-10 code(s) and severity
- ✓ Failed prior therapies with dates, doses, durations, and reasons for discontinuation
- ✓ Clinical rationale citing FDA labeling and guidelines
- ✓ Peer-reviewed evidence references
- ✓ Specific request (drug, dose, duration, route)
- ✓ Prescriber attestation and signature
Step-by-Step: Writing the Letter
Start with a one-sentence summary stating the patient, diagnosis, and request. Reviewers often skim — front-load the ask.
Next, document the diagnosis with the most specific ICD-10 code possible. Include severity, laterality, and any comorbidities that affect treatment selection.
In the prior therapies section, be concrete. "Failed methotrexate" is weak. "Methotrexate 25mg weekly from 03/2024 to 09/2024, discontinued due to elevated transaminases (AST 142, ALT 168)" is strong.
When citing evidence, link to the most recent guideline (e.g., NCCN, ACR, ADA) and reference the specific recommendation by number. Then add 1-2 randomized controlled trials that support the choice.
Close with the specific request: drug name, dose, frequency, route, and intended duration. Sign and date.
Payer-Specific Pitfalls
Each payer has its own quirks. Aetna wants you to cite the Clinical Policy Bulletin number. UnitedHealthcare wants OptumRx policy references. Cigna wants Coverage Policy numbers. Generic LMNs get denied; payer-tailored LMNs get approved.
Common Mistakes That Cause Denials
Most LMN denials stem from a small set of fixable errors:
- ✓ Missing dates on prior therapy trials
- ✓ No ICD-10 specificity
- ✓ Citing outdated guidelines
- ✓ Forgetting to address step therapy
- ✓ Failing to reference the payer's own medical policy
- ✓ No clear request statement
How RxCheckUp Helps
RxCheckUp generates LMNs that are pre-tailored to the payer's exact medical policy, with citation hyperlinks to the clinical evidence. The clinician reviews and signs — no blank-page writing required.