How to Write a Letter of Medical Necessity (Free Template)

The clinical letter that turns "not medically necessary" into an approval — what it includes, how to ask your doctor, and a template you can hand them today.

By the Fight Back editorial team · Banana Bay Press · Updated July 26, 2026

A letter of medical necessity is a document from your treating provider explaining why a specific service, medication, or device is medically necessary for you. It names your diagnosis, the clinical reason for the request, treatments you already tried and why they failed, and how the request meets your plan's coverage rules. You get one by asking your doctor's office to write it.

What a letter of medical necessity is

When an insurer denies a claim as "not medically necessary," it is saying the requested care does not meet its coverage criteria for your situation. A letter of medical necessity (sometimes called an "LMN") is the clinical answer to that objection. It is written by the provider who is treating you and explains, in medical terms, why this specific service or medication is appropriate and necessary for your condition.

HealthCare.gov lists "not medically necessary" as one of the reasons an insurer may deny coverage — and it explicitly notes that when you appeal, you can include additional information for the insurer to consider, "such as a letter from the doctor." That letter is often the single most persuasive piece of evidence in an appeal, because coverage decisions turn on your plan's definition of medical necessity, and your provider is the person qualified to speak to it.

The letter is not the same as your appeal. Your appeal is your formal request to reconsider; the medical necessity letter is the clinical exhibit attached to it. If you are still deciding how to file, start with our guide on how to appeal a denied health insurance claim and use this letter as your supporting document.

Who writes it (and how to ask your doctor)

The letter carries the most weight when it comes from the clinician who ordered the service or prescription — usually your physician, but it can also be a specialist, nurse practitioner, physician assistant, or therapist. Their professional judgment is exactly what the insurer is weighing, so the letter must be on their letterhead and carry their signature and credentials.

You do not have to wait passively. Many offices are glad to write these letters, but they are busy, so make it easy:

Call the office and ask specifically for a "letter of medical necessity" for the denied service. Give them the denial reason from your notice.
Send them the denial letter and your Explanation of Benefits so they can see exactly what code and service were denied and why.
Offer a draft. You can prepare the facts you know — your history, the alternatives you tried, and how the condition affects daily life — and let the provider add the clinical rationale and sign. The template below is built for exactly this.
Ask about the deadline. Appeals have time limits, so tell the office when your appeal is due and confirm they can turn the letter around in time.

What a strong letter includes

Patient-advocacy sources that review these letters point to a consistent set of elements. A strong letter of medical necessity typically covers:

Patient and policy identifiers — name, date of birth, and member/policy ID so the insurer can match the letter to your file.
The diagnosis and its code. The specific condition, ideally with the ICD-10 diagnosis code, so the request is tied to a defined medical problem.
The exact service, medication, or device requested — including strength, frequency, or duration where relevant.
The clinical rationale. Why this care is necessary for you: symptoms, severity, functional impact, and the expected benefit.
Alternatives already tried and their outcomes. Which treatments you attempted first, for how long, and why they failed or caused intolerable side effects. This is what answers a step-therapy requirement, where the insurer wants cheaper options tried first.
A tie to the plan's own coverage criteria. Referencing the plan's medical-necessity language or published clinical guidelines shows the request meets the insurer's own standard, not just the doctor's preference.
Supporting evidence. Relevant test results, chart notes, or treatment guidelines from a recognized medical body can be cited or attached.
Provider signature and credentials on office letterhead, with contact details.

If your denial is specifically about a prescription drug, our companion guide on what to do when insurance denied my medication walks through formulary exceptions and step-therapy overrides in more detail.

Free template you can hand your doctor

Copy the skeleton below into a document, fill in the brackets with what you know, and give it to your provider's office to finish and sign. It is a starting point, not a finished letter — your doctor should adjust the clinical language to fit your case.

[Practice / Provider Letterhead] [Date] [Insurance Company Name] Attn: Appeals / Utilization Review [Insurer Address] RE: Letter of Medical Necessity Patient Name: [Full Name] Date of Birth: [MM/DD/YYYY] Member / Policy ID: [Member ID] Claim / Reference Number: [Claim # from denial notice] Date of Denial: [Date on denial letter] To Whom It May Concern: I am the treating [physician / specialty] for [Patient Name], and I am writing to explain why the requested [service / medication / device] is medically necessary for this patient. Diagnosis: [Diagnosis] (ICD-10 code: [e.g., XXX.XX]) Requested service / treatment: [Name of service, medication, or device; include dose, frequency, or duration if applicable; procedure code if known]. Clinical background and rationale: [Describe the patient's condition, symptoms, severity, and how it affects daily function. Explain why the requested treatment is appropriate and what outcome it is expected to achieve.] Treatments already tried: - [Treatment 1] — [dates / duration] — [result: ineffective / side effects / contraindicated] - [Treatment 2] — [dates / duration] — [result] [Explain why these alternatives failed or are not suitable, addressing any step-therapy requirement.] Coverage criteria: The requested treatment meets the medical-necessity criteria described in [reference the plan's coverage policy or a recognized clinical guideline]. Denying it would [describe the clinical risk of going without it]. Based on my clinical judgment, [requested service] is medically necessary for [Patient Name]. I respectfully request that this denial be overturned and the service approved. Please contact my office with any questions. Sincerely, [Provider Name, credentials] [Specialty] [Practice name, phone, and NPI if applicable] Enclosures: [chart notes, test results, guidelines, prior authorization, as applicable]

Tip: Keep the original of every document and send the insurer copies. Reference the exact claim or reference number from your denial notice on the letter so it lands in the right file, and confirm the mailing address or fax/portal your plan uses for appeals — the address on a bill is often not the appeals address.

Common mistakes that get letters rejected

Even a well-meaning letter can fall flat. The patterns that weaken these letters most often:

Being vague. "This patient needs this medication" without a diagnosis, a code, or specifics gives the reviewer nothing to match against the plan's criteria.
Skipping the failed alternatives. If the plan uses step therapy and the letter does not document what was tried first and why it failed, the reviewer can uphold the denial on that basis alone.
Ignoring the plan's own language. The strongest letters answer the specific denial reason and point to the plan's coverage policy or a recognized guideline — not just the provider's preference.
Missing identifiers or the wrong claim number. A letter that can't be matched to your file, or that references the wrong claim, can be set aside.
No signature or credentials. An unsigned letter, or one not on provider letterhead, carries far less weight than a signed clinical statement.
Missing the deadline. The best letter is worthless if it arrives after your appeal window closes. Verify the deadline on your denial notice.

A tight, specific, signed letter that answers the denial reason head-on is what moves a reviewer. For the full appeal process — deadlines, external review, and how the letter fits in — see our appeals walkthrough, or grab the free cheat sheet below.

Get the free 5-Minute Denial Cheat Sheet

The exact steps, deadlines, and the letter that wins — one page, instant download.

Get the free cheat sheet → Want the done-for-you version? The Insurance Denial Appeal Kit ($27) →

Frequently asked questions

Who has to write a letter of medical necessity?

The letter carries the most weight when it comes from the treating provider who ordered the service or prescription — usually your physician, but it can also be a specialist, nurse practitioner, physician assistant, or therapist. You can draft supporting details yourself, but the clinician signs it and confirms the clinical facts.

Is a letter of medical necessity the same as an appeal letter?

No. An appeal letter is your formal request to the insurer to reconsider a denial. A letter of medical necessity is the clinical document your doctor writes to justify why the service is needed. In an appeal, the medical necessity letter is usually attached as supporting evidence alongside your appeal request.

What is an ICD-10 code and why does the letter need one?

ICD-10 codes are the standard diagnosis codes used across U.S. health care. Including the diagnosis code ties the requested service to a specific medical condition, which helps the insurer match your request against its coverage criteria. Your doctor's office has these codes on file.

What is step therapy and why does it matter in the letter?

Step therapy is an insurer rule that requires you to try cheaper or preferred treatments first before it will cover another option. A strong letter lists which alternatives you already tried, for how long, and why they failed or caused side effects — showing you have already met or should be exempt from the step-therapy requirement.

Does a letter of medical necessity guarantee approval?

No document guarantees approval. A clear, specific letter that ties your diagnosis to the plan's own coverage criteria and documents failed alternatives gives your appeal its best chance, but the insurer still makes the final coverage decision under your plan's terms.

Can I write the letter myself and have my doctor sign it?

You can prepare a draft with the facts you know — your history, prior treatments, and how the condition affects daily life — to save your doctor time. But the clinical rationale and the signature must come from the provider, because the insurer is relying on their professional judgment.

Sources & further reading: HealthCare.gov — Internal appeals; Patient Advocate Foundation — Things to include in your appeal letter; NAIC — What Is Medical Necessity?