How to Write a Medical Necessity Letter (With Templates)

If there is one document that can make or break an insurance appeal, it is the Letter of Medical Necessity (LMN). This letter, written by your physician, is the clinical backbone of your case. A weak, generic LMN will be dismissed. A strong, specific LMN can overturn denials that seem hopeless. This guide explains exactly what the letter must contain, provides a template, and tells you how to work with your doctor to produce the best possible document.

What Is a Letter of Medical Necessity?

A Letter of Medical Necessity is a formal document written by a licensed physician or other healthcare provider explaining to an insurance company why a specific treatment, medication, procedure, or device is medically required for a patient's condition. It is not a prescription or a referral — it is a clinical argument written to a reviewer.

Insurers deny claims based on their internal medical criteria. The LMN is your doctor's direct response to those criteria — a professional-to-professional clinical case that the denied service is not just desired but medically necessary for your specific situation. When paired with a strong appeal letter, an LMN is the most effective tool in the entire insurance appeal process.

The Eight Essential Elements of a Strong LMN

A persuasive Letter of Medical Necessity must include all of the following:

  1. Patient Identification. Full name, date of birth, insurance member ID, and date of service.
  2. Diagnosis. The specific diagnosis or diagnoses, with ICD-10 codes. Include comorbidities that are relevant to the need for the treatment.
  3. Clinical History Summary. A brief summary of relevant medical history — how long the patient has had this condition, its progression, and its functional impact.
  4. Treatments Previously Tried. List every treatment that has been attempted and failed or was contraindicated. This is especially critical for step therapy denials and prior authorization cases. Be specific: drug name, dose, duration, and why it did not work.
  5. Description of the Requested Treatment. Exactly what is being requested (procedure code, drug name and dose, device type, etc.) and the proposed treatment plan.
  6. Clinical Rationale. Why this specific treatment is medically necessary for this patient. Reference published clinical guidelines (e.g., AHA, ACS, ASCO, specialty society guidelines) and peer-reviewed studies that support the prescribed treatment as the standard of care.
  7. Why Alternatives Are Inadequate. Directly address the insurer's stated denial reason. If they denied because a cheaper alternative exists, explain why that alternative is not clinically appropriate for this patient.
  8. Consequences of Denial. What will happen if the treatment is not provided? Be specific and clinical: deterioration, hospitalization risk, permanent injury, etc.

Letter of Medical Necessity Template

The following is a general template. Have your physician customize it thoroughly with specific clinical details.

[Physician Name, MD/DO/NP/PA]
[Specialty]
[Practice Name]
[Address]
[Phone] | [Fax] | [NPI Number]
[Date]


To the Medical Review Department,
[Insurance Company Name]
[Address]


RE: Letter of Medical Necessity for [Patient Full Name]
Date of Birth: [DOB]
Member ID: [ID]
Claim Number: [Claim #]
Denied Service: [CPT/NDC code and description]


Dear Medical Reviewer:


I am writing to support my patient [Name]'s appeal of the denial of [treatment/medication/procedure]. I have treated this patient since [date] for [diagnosis] (ICD-10: [code]).


Clinical History: [2–3 sentences describing the patient's condition, severity, and functional impact.]


Prior Treatments: The patient has previously attempted the following treatments without adequate response: [list treatments, doses, duration, and outcomes].


Requested Treatment: I am requesting [treatment] for the following clinical reasons: [detailed clinical rationale, citing specific guidelines or studies].


Why Alternatives Are Inadequate: [Specific explanation of why the insurer's suggested alternative is not clinically appropriate for this patient.]


Consequences of Denial: Without this treatment, I anticipate [specific clinical consequences].


I respectfully request that this denial be reversed. I am available to discuss this case at [phone number].


Sincerely,
[Physician Signature]
[Physician Name, Credentials]
[NPI Number]

How to Work with Your Doctor to Get a Strong Letter

Most physicians are sympathetic to patients fighting insurance denials but are extremely busy. To get the best letter possible, make their job easy:

  • Schedule a dedicated appointment to discuss the appeal — do not ask the staff to fit the letter into a regular visit.
  • Bring the denial letter so your doctor can see exactly what argument the insurer made.
  • Bring a copy of the template above as a starting point. Offer it as a draft for their review.
  • Ask your doctor to reference specific clinical guidelines relevant to your condition (they will know which ones).
  • Ask the letter to address the specific denial reason head-on — not just generic medical necessity, but the insurer's exact objection.

Once you have the LMN, bundle it with your appeal letter (use the free appeal letter builder), supporting medical records, and any other documentation. See the full insurance appeal guide for everything else you need to submit.

Frequently Asked Questions

Who should write the Letter of Medical Necessity?
The letter should be written by the treating physician or specialist who prescribed or recommended the denied treatment. Letters from a primary care physician who has not personally evaluated the condition are less compelling. The more specialized the author, the stronger the letter.
Does the letter need to be on official letterhead?
Yes. The letter should be on the physician's official office letterhead, dated, signed, and include the physician's name, credentials, contact information, NPI number, and the patient's name and date of birth.
How long should a Letter of Medical Necessity be?
One to three pages is typical. It should be thorough but focused. A long letter is fine if every sentence adds clinical value. Avoid padding with irrelevant background. The reviewer is a medical professional — lead with the clinical facts.
What if my doctor refuses to write a Letter of Medical Necessity?
A doctor who prescribes a treatment should be willing to write a letter supporting it. If they refuse, ask why — it may be a simple misunderstanding about what is needed. If they remain unwilling, consider consulting with a specialist for a second opinion who may be more supportive. You can also ask the doctor's office manager or patient advocate to help facilitate the request.

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