What Is a Letter of Medical Necessity?

A letter of medical necessity (LMN) is a document from your doctor explaining why a specific treatment, medication, or procedure is medically necessary for your condition. It's often the most important piece of an insurance appeal.

Who Writes It?

Your treating physician writes the letter. Specialists carry more weight than primary care doctors for specialty treatments, but any treating physician can write one.

What It Should Include

  1. Patient information: Name, date of birth, policy number
  2. Diagnosis: Specific ICD-10 codes and clinical description
  3. Treatment requested: Exact procedure, medication, or service
  4. Medical justification: Why this specific treatment is necessary
  5. Alternatives tried: Previous treatments and why they failed
  6. Consequences of denial: What happens without this treatment
  7. Supporting evidence: Peer-reviewed studies, clinical guidelines

Tips for a Strong LMN

  • Use clinical language, not layman's terms
  • Reference the insurer's own coverage criteria and explain how you meet them
  • Include specific test results, lab values, and imaging findings
  • Cite current peer-reviewed medical literature
  • Address the specific reason for the denial
  • Be concise but thorough — typically 1-2 pages

When You Need One

  • Prior authorization denials
  • Medical necessity denials
  • Step therapy exceptions
  • Formulary exceptions
  • Out-of-network exceptions

Need Help Writing Your Appeal?

Our AI-powered tool analyzes your denial letter and generates a personalized appeal in minutes. Upload your denial and get started for free.

Start Your Free Appeal

Frequently Asked Questions

Can I write my own letter of medical necessity?

The letter should come from your physician, but you can draft talking points or a template for them. Many doctors appreciate this because it saves them time. Just make sure they review, modify, and sign it on their letterhead.

How long should the letter be?

Typically 1-2 pages. Be thorough but concise. The reviewer reads many letters, so clear structure with bullet points and cited evidence is more effective than lengthy narratives.

Related Resources