If your doctor recently mentioned a letter of medical necessity, you’re probably wondering, what is a medical necessity letter, and why do you need one? In simple terms, it’s a signed note from your healthcare provider that explains why a treatment, service, or product is medically needed for your health. Insurance companies, HSA and FSA administrators, and even employer benefit plans often ask for this letter before they approve or reimburse certain expenses.
This guide walks you through the basics: how to get a letter of medical necessity from your provider, how to write a letter of medical necessity if you’re a provider drafting one, and how to use a letter of medical necessity once you have it in hand. We’ll also cover when you might need a letter of medical necessity for medication, weight loss treatment, or medical equipment, plus the benefits and safety details worth knowing before you request one.
A medical necessity letter (often shortened to LMN) is a short document your healthcare provider writes on your behalf. It usually spells out:
Insurers, health savings account (HSA) administrators, and flexible spending account (FSA) plans use this letter to decide whether an expense qualifies for coverage or reimbursement. Without it, a claim can get denied simply because the item looks like a personal purchase rather than a medical one.
Items that commonly require this kind of documentation include:
Not every prescription needs extra paperwork. But this kind of documentation for a medication usually comes into play when:
This comes up often with newer weight loss medications, since insurers want proof that the prescription is tied to a diagnosed condition, such as obesity or type 2 diabetes, rather than general fitness goals. If you’re starting treatment through an online weight loss clinic, your provider can usually prepare this documentation as part of your visit, so you don’t have to chase it down later on your own.
Here’s the simplest path to getting one:
Knowing this process ahead of time saves you from last-minute delays. Many providers, including telehealth clinics, can turn a request around within a few business days.
If you’re a healthcare provider drafting one of these letters, keep it clear and specific. Vague language is the most common reason a letter gets rejected. Here’s what a strong letter usually includes:
Element | What to Include |
|---|---|
Patient Information | Full name, date of birth, plan or member ID |
Diagnosis | Specific medical condition, ICD-10 code if available |
Recommended Treatment | Product, service, or medication being prescribed |
Medical Justification | Why this treatment addresses the diagnosis |
Duration | Expected length of treatment or ongoing need |
Provider Details | Name, credentials, signature, license number, date |
Drafting this kind of letter really comes down to answering one question clearly: why does this specific patient need this specific treatment? The more precise the explanation, the fewer questions a reviewer will have.
Once you have the letter in hand, here’s how to make the most of it:
If a claim is denied, this same letter can also serve as supporting evidence during an appeal.
If you’d like help figuring out whether your treatment qualifies, our team can walk you through exactly what a medical necessity letter needs to include for your specific situation.
This kind of letter is a helpful tool, but it isn’t a guarantee. Keep the following in mind:
For an official breakdown of which expenses the IRS considers medically necessary, its Publication 502 on medical and dental expenses is a reliable reference point.
Independent health resources like GoodRx’s guide to letters of medical necessity also break down which situations commonly call for this documentation.
Situation | Likely Need a Letter? |
|---|---|
Prescription medication for an FDA-approved use | Usually not |
Weight loss medication or program | Often, yes |
Compounded or off-label medication | Yes |
CPAP machine or medical equipment | Often, yes |
Gym membership for a diagnosed condition | Yes |
Routine doctor visit copay | No |
Hot tub for a diagnosed medical condition | Often, yes |
To sum up: a medical necessity letter is simply your provider’s written confirmation that a treatment is medically needed, not just a preference. Whether you’re seeking coverage for medication, equipment, or a weight loss program, knowing how to draft one, or how to request one from your provider, can make the difference between a denied claim and a smooth reimbursement.
Ready to talk to a provider about your treatment options? Reach out to our care team today, and let us help you get the documentation you need so you can focus on your health, not the paperwork.
Only a licensed healthcare provider who is actively treating you can write one, such as a physician, nurse practitioner, or physician assistant. Insurers and FSA/HSA administrators won’t accept a letter drafted by the patient or a family member.
No. Plan administrators specifically require a licensed provider’s signature and credentials, since the whole point of the letter is an independent medical opinion confirming the treatment is necessary.
Most letters are good for about 12 months from the date they’re signed. After that, your plan may ask your provider to issue an updated version, especially for ongoing treatments.
Not automatically. It strengthens your case and gives the reviewer the clinical context they need, but your insurer or plan administrator still has the final say on approval.
Ask your provider whether the letter can be made more specific, for example by adding an ICD-10 code or a clearer explanation of the treatment timeline, and then resubmit it as part of a formal appeal.
