What is a Letter of Medical Necessity? How to Write One in 2025

Insurance paperwork can slow everything down. You know what the patient needs, but getting approval often means jumping through hoops.

One of the most common (and frustrating) parts of the process is writing a letter of medical necessity.

A letter of medical necessity is something written by a healthcare professional that justifies medical treatment for a diagnosis and is used for insurance purposes.

In this article, we'll give an overview of what a letter of medical necessity is and how you can write one in 2025. Let's dive in!

What is a Letter of Medical Necessity?

A letter of medical necessity is a written explanation from a healthcare provider that outlines why a specific treatment, service, medication, or item is essential for a patient's care.

It supports the clinical need for the recommendation and is often required by insurance companies during the approval process. A letter of medical necessity is used to:

Request prior authorization for treatments or services.
Justify coverage for medications or equipment not usually covered by insurance.
Support appeals for denied insurance claims.
Document the need for continued care or specialized interventions.
Clarify why a specific option is medically necessary over standard alternatives.

The letter should be clear, specific, and tied directly to the patient’s diagnosis and treatment plan. A strong letter helps reduce insurance denials and delays in care.

3 Things a Letter of Medical Necessity Should Do

A good letter of medical necessity isn’t just about stating a diagnosis, it needs to make a clear case for why the recommended care is required. Insurance reviewers look for specific elements that prove the request is valid and medically appropriate.

Here are three things a letter of medical necessity should do:

State the Patient’s Condition - Clearly explain the diagnosis and how it affects the patient's daily life or health outcomes. Include relevant clinical findings or history.
Describe the Recommended Treatment - Provide details about the specific service, item, or medication being requested. Mention how it relates to the patient’s diagnosis and treatment goals.
Justify Medical Necessity - Explain why the requested care is essential, not elective or experimental. Use clinical guidelines, past treatment attempts, or expected outcomes to support the case.

These three points help ensure the letter is complete, persuasive, and aligned with what insurers need to approve care.

How to Write a Letter of Medical Necessity

When writing a letter of medical necessity, it's important to stay focused, structured, and specific. Each section should clearly explain how the recommended care relates to the patient’s diagnosis and why it is required.

Here's how to write a letter of medical necessity:

Start With Patient and Provider Information

Include the patient’s full name, date of birth, insurance ID, and diagnosis codes. Then, add your name, credentials, NPI number, practice name, and contact information.

This information ensures that the letter is tied to the correct claim and confirms your role in the patient’s care. Use a structured format or template that follows insurance or payer guidelines to avoid missing key details.

Summarize Medical History

Give a short overview of the patient’s relevant medical background. Any previous information that is relevant to the current diagnosis is good to add.

Highlight any previous treatments, failed attempts, or recent changes in condition that support the current request. This shows why the new treatment is necessary now.

Describe the Requested Treatment

Clearly explain the treatment, service, item, or medication you are recommending. Include the name, dosage, frequency, or duration if applicable.

Make sure to tie it back to the diagnosis and how the requested treatment is the best option.

Justify Medical Necessity

This is the most important part. Use evidence, clinical guidelines, or past treatment outcomes to explain why the recommended care is essential. Emphasize that it is not elective, cosmetic, or experimental.

Attach Supporting Documentation

Mention that you are including lab results, imaging, chart notes, or denial letters. Anything that is relevant to the diagnosis and treatment plan.

These materials strengthen your case. Refer to them in the body of the letter when possible.

End With Signature and Date

Sign the letter with your full name and title, and include the date. Make sure everything matches your records. This formalizes and completes the documentation.

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Letter of Medical Necessity Templates and Examples

A structured format can help you save time and ensure you include all the key information insurers look for.

Here are some templates and examples of letters of medical necessity. Use these as a base and edit them to meet payer-specific requirements.

Patient Letter of Medical Necessity Template

This version is written to support the patient’s request for coverage and outlines the clinical reasoning for the recommendation.

Letter of Medical Necessity

[Physician's Letterhead]
[Date]

[Medical Director or Claims Reviewer]
[Title]
[Health Insurance Company Name]
[Insurance Company Address]
[City, State, ZIP Code]

RE: Request for Coverage – [Treatment/Medication Name]

Patient Name: [Patient Name]
Date of Birth: [DOB]
Diagnosis: [Diagnosis], [ICD-10-CM Code]
Policy/Group Number: [Policy Number]
Policyholder: [Policyholder Name]

Dear [Medical Director/Reviewer Name],

I am writing to request coverage for [Treatment/Medication Name] for my patient, [Patient Name], who has been diagnosed with [Diagnosis]. This treatment is medically necessary based on their condition, symptoms, and response to previous care.

Patient Medical History and Diagnosis
[Patient Name] is a [Age]-year-old patient under my care since [Start Date]. They were diagnosed with [Diagnosis] on [Date], and their symptoms include [Brief Symptom Overview]. Previous treatments including [List Previous Treatments] have been ineffective.

Rationale for Treatment
The requested treatment is necessary to manage the patient’s condition and improve their health outcomes. Alternatives have been attempted and either failed or were not appropriate based on contraindications. This recommendation follows current clinical guidelines and is supported by [List Any Relevant Sources or Guidelines].

Please review the attached documentation, which includes medical records and supporting test results. Contact me at [Phone Number] if you require additional information.

Sincerely,
[Physician Name, Credentials]

Enclosures: [List attachments]

Doctor Patient Letter of Medical Necessity Template

This version focuses more on the clinical details and can be used for formal documentation when submitting to insurers.

Letter of Medical Necessity

[Physician's Letterhead]
[Date]

[Insurance Representative Name]
[Title]
[Insurance Company Name]
[Company Address]
[City, State, ZIP Code]

RE: Letter of Medical Necessity for [Treatment/Service Name]

Patient Name: [Patient Name]
DOB: [Date of Birth]
Diagnosis: [Diagnosis], [ICD-10-CM Code]
Insurance ID: [ID Number]
Policyholder: [Policyholder Name]

Dear [Representative Name],

I am submitting this letter to confirm the medical necessity of [Treatment/Service Name] for [Patient Name], who is currently under my care for [Diagnosis]. This intervention is critical to improve or maintain functional ability and prevent further decline.

Medical Background
[Patient Name] has been experiencing [Brief Summary of Condition] and was first diagnosed on [Diagnosis Date]. Their clinical status has remained [Description] despite attempts with [List Prior Interventions]. Diagnostic results including [List Labs/Scans] support this request.

Justification and Treatment Rationale
Based on clinical judgment and guidelines, [Treatment/Service Name] is the most appropriate next step. Alternative treatments have been exhausted or are not suitable. Expected benefits include [Brief Outcome], and treatment aligns with evidence-based standards.

Attached are relevant records supporting this request. If more information is needed, please contact me directly.

Sincerely,
[Provider Name, Credentials]

Enclosures: [List Enclosures]

Letter of Medical Necessity FAQ

Who Can Write a Letter of Medical Necessity?

A letter of medical necessity must come from a licensed healthcare provider directly involved in the patient’s care. The person writing the letter should be qualified to assess the condition and recommend treatment.

Here are a few people who can typically write a letter of medical necessity:

Physicians (MD or DO)
Nurse Practitioners (NP)
Physician Assistants (PA)
Therapists (PT, OT, SLP)
Psychologists or Psychiatrists
Dentists (for dental-related care)

The provider’s credentials and role should match the type of treatment or service being requested.

What Exactly Is "Medical Necessity"?

The term "medical necessity" refers to services or items that are essential for diagnosing, preventing, or treating a medical condition. They must be clinically appropriate, not primarily for convenience, and meet accepted standards of care.

Insurance companies often follow specific criteria when deciding if something meets their definition of medical necessity.

Are Letters of Medical Necessity Important For Insurance?

Letters of medical necessity play a key role in getting treatments approved, especially when the service isn’t routinely covered. A strong letter can make the difference between a fast approval and a delayed or denied claim.

Here's why letters of medical necessity are important for insurance purposes:

Support Prior Authorization Requests - Many insurance plans require a letter to approve non-standard treatments, medications, or equipment.
Strengthen Appeals After Denials - If coverage is denied, a well-written letter can be submitted during the appeal process to explain why the service is necessary.
Document Medical Decision-Making - It shows that the recommendation is based on clinical judgment, not patient preference or convenience.
Reduce Processing Delays - Including a complete and structured letter up front can avoid back-and-forth with insurance reviewers.

These letters aren't just helpful—they're often required for approvals and can save time and effort later on.

Write Stronger Letters, Get Faster Approvals

A well-written letter of medical necessity can reduce delays, avoid denials, and help your patients get the care they need. Stick to a clear format, back up your recommendations with clinical reasoning, and customize each letter to fit the situation.

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