Key takeaways:
A letter of medical necessity (LOMN) is a document from your healthcare professional recommending a particular treatment, product, or device for medical purposes.
The letter often includes relevant healthcare history along with information about the medical necessity and duration of the treatment being recommended.
You may need an LOMN for the reimbursement of a procedure, product, or device when you use funds from your health savings account (HSA), flexible spending account (FSA), or health reimbursement arrangement (HRA).
Health insurance covers a wide variety of services, treatments, and products. But some items — such as vitamins, supplements, and exercise equipment — typically aren’t covered.
You can use tax-advantaged funds from your health savings account (HSA), flexible spending account (FSA), or health reimbursement arrangement (HRA) to pay for certain expenses that aren’t covered by insurance. However, if your purchase isn’t considered a qualified medical expense by the IRS, you may need a letter of medical necessity, or LOMN, from your healthcare professional to verify that the product or service is required for you to maintain your health.
What is the purpose of a letter of medical necessity?
A letter of medical necessity explains why your healthcare professional is recommending a specific treatment or product for you. This document verifies that the expense is for the diagnosis, treatment, or prevention of an illness or medical condition, rather than for general health purposes. If the purchase does not meet these requirements, it will not be considered a qualified expense by the IRS and typically won’t be eligible for reimbursement by your HSA, FSA, or HRA administrator.
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Let’s say your doctor recommends that you take iron supplements that aren’t covered by your health plan to treat iron-deficiency anemia. You will need an LOMN to obtain reimbursement for the supplements when you use your tax-advantaged account funds.
When is a letter of medical necessity required?
You usually need a letter of medical necessity for medical procedures or products that are excluded from health insurance coverage. You may be asked for an LOMN from your:
FSA administrator
HSA administrator
HRA administrator
Private insurance company
You may also need an LOMN if you are taking deductions on your taxes for medical expenses or appealing an insurance denial.
What are some items that require a letter of medical necessity?
It’s not always clear if a product or service is considered an eligible expense by an insurance plan or tax-advantaged account.
If you have insurance, it’s important to contact your plan to get a better idea of what’s covered. If you have an FSA, HSA, or HRA, you can contact your account administrator to determine if an expense would be approved for reimbursement. As mentioned, certain items may require a letter of medical necessity to be considered eligible.
Some items that aren’t typically considered qualified medical expenses may need an LOMN. These include:
Baby formula
Counseling
Exercise equipment
Fitness trackers
Fluoride toothpastes and rinses
Gastric bypass surgery
Supplements
Vitamins
Who writes a letter of medical necessity?
Generally, your medical professional writes and signs a letter of medical necessity. An LOMN can improve your chance of reimbursement for a product or service. However, it doesn’t guarantee that an expense will be approved.
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Some examples of medical professionals who can write an LOMN are:
Nurse practitioners
Physicians
The medical professional who writes the LOMN must be the person who is treating you. If you’re submitting an LOMN to your insurance company, it’s a good idea to ask if there’s a preference about what kind of clinician submits the document.
How do you get a letter of medical necessity?
Start by checking with your FSA, HSA, or HRA administrator or insurance company to find out if you need a letter of medical necessity. You can also ask if there’s a specific form or template you need to use.
Next, ask the healthcare professional who is treating you to write the letter or complete the form. The document or letter should explain your diagnosis; why the recommended product, service, or treatment is medically necessary for you; and how long you’ll need it.
What does a letter of medical necessity include?
Some insurance plans as well as FSA, HSA, and HRA account administrators provide templates for letters of medical necessity. Here are some examples:
Generally, your healthcare professional needs to include the following information in an LOMN:
Your name and medical history
Your diagnosis
Reason the product or service is needed
Duration of treatment
Date the letter was written
Their relationship to you, contact information, and signature
Example of a letter of medical necessity
A letter of medical necessity doesn’t have to follow one specific format. For example, HealthEquity allows a healthcare professional to submit a letter instead of its form, as long as the required information is included.
Here’s an example of what an LOMN might look like, with you adding your specific information in the brackets:
[Date]
To whom it may concern:
I am treating [patient name] for [diagnosed medical condition]. I recommend [specific product, service, or treatment] to treat this condition.
[Explain how the recommended product, service, or treatment will help improve the diagnosed condition.]
This treatment is medically necessary from [start date] through [end date].
Sincerely,
[Healthcare professional’s name and credentials]
[License number]
[Contact information]
[Signature]
How do I use a letter of medical necessity?
The following is an example of when a letter of medical necessity would come in handy, what information is typically included, and how to make a submission.
Suppose your body mass index (BMI) is 41, which is generally considered high, and you have had a high BMI for years. As a result, your healthcare professional recommends weight-loss surgery. But your insurance company requires an LOMN for the procedure to qualify for reimbursement. Your healthcare professional might include the following information in the LOMN:
Diagnosis of obesity
References to studies that show the effectiveness of weight-loss surgery
Information about your attempts to lose weight other ways, such as prescription weight-loss medication
Information about any chronic illnesses you have that could be improved by weight loss, such as Type 2 diabetes, hypertension, or sleep apnea
Then, the LOMN would be submitted to the insurance company for review. If the claim is denied, you could submit an appeal.
Tips on how to write a letter of medical necessity
It’s important that an LOMN includes a detailed description of your medical condition, as well as the product or service being recommended. This means that your clinician will need to include a thorough account of your medical history, including information about any past treatments you’ve tried.
Next, your clinician will need to demonstrate why the product or service is necessary for diagnosing or treating your condition. To do this, they can provide information about relevant clinical studies and research. They must also state how long you’ll need the product or service.
An LOMN should not be phrased like a demand. The focus should be on why a product or service is medically required for you.
How long is a letter of medical necessity good for?
An LOMN may be valid for up to 1 year. After that, you will likely need to get a new letter. If you need a product or service for longer than the time specified on an LOMN, you will need to get a new letter. If you don’t have a current LOMN, you may not be reimbursed for expenses incurred after the original timeframe.
Frequently asked questions
Generally, no. Letters of medical necessity are typically written and signed by the healthcare professional who is treating you.
Possibly. A healthcare professional may write an LOMN if red light therapy is recommended to treat a diagnosed medical condition. But an LOMN may not always be required, so check with your FSA, HSA, or HRA administrator to find out what documentation you need.
Ambulance transportation for a nonemergency situation may be considered medically necessary when your condition makes other forms of transportation unsafe. For example, this could include being unable to walk or sit in a chair or wheelchair.
Generally, no. Letters of medical necessity are typically written and signed by the healthcare professional who is treating you.
Possibly. A healthcare professional may write an LOMN if red light therapy is recommended to treat a diagnosed medical condition. But an LOMN may not always be required, so check with your FSA, HSA, or HRA administrator to find out what documentation you need.
Ambulance transportation for a nonemergency situation may be considered medically necessary when your condition makes other forms of transportation unsafe. For example, this could include being unable to walk or sit in a chair or wheelchair.
The bottom line
A letter of medical necessity (LOMN) demonstrates that a healthcare service, treatment, or item is needed for medical purposes. Your health insurance plan — or the administrator of your health savings account (HSA), flexible spending account (FSA), or health reimbursement arrangement (HRA) — may request an LOMN before reimbursing an expense.
An LOMN is typically written by your healthcare professional and includes information about your diagnosis and duration of treatment. It should also include the reason a treatment, product, or service is needed. An LOMN does not guarantee that your expense will be approved. However, it can increase your chances of getting coverage or reimbursement for an expense.
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References
Aetna. (n.d.). Template letter of medical necessity for Aetna.
Anthem. (2026). Clinical UM guidelines: Ambulance services; ground; non-emergent.
Association of Accredited Naturopathic Medical Colleges. (n.d.). What is naturopathic medicine?
Astellas Pharma. (2021). Sample letter template of medical necessity for Astellas products.
CMS.gov. (2009). Certificate of medical necessity. U.S. Department of Health and Human Services.
FSA Store. (n.d.). What is LMN eligible?
HealthEquity. (n.d.) HRA/FSA letter of medical necessity.
Internal Revenue Service. (2026). Publication 502 (2025), medical and dental expenses.
Internal Revenue Service. (2026). Understanding your IRS notice or letter.
Metropolitan Life Insurance. (2026). What is a letter of medical necessity (LMN) and who may need one?
Mitsubishi Tanabe Pharma America. (2025). Sample letter of medical necessity.
Office of Inspector General. (n.d.). Osteogenesis stimulators: Lump-sum purchase versus rental. U.S. Department of Health and Human Services.
United Healthcare. (n.d.). Template letter of medical necessity for United HealthCare.
Via Benefits. (n.d.). Letter of medical necessity. Extend Health.
