What Is a Letter of Medical Necessity (and Why Should You Care?)

Have you ever tried to use your Flexible Spending Account (FSA) for a health expense, only to be told, “Sorry, you need a Letter of Medical Necessity”?

Sounds official (and a little intimidating).

But don’t worry. A Letter of Medical Necessity (or LMN, for short) is actually pretty simple and it can save you money.

Find out more about this important piece of paperwork and why it matters for some of your healthcare expenses.

So … What Is a Letter of Medical Necessity?

A Letter of Medical Necessity is a note from a licensed healthcare provider, like your doctor or nurse practitioner. It explains that a certain product, service, or treatment is medically necessary for your specific health condition, not just a “nice to have.”

Think of it like a permission slip for your FSA. Your doctor says, “Yes, this is needed,” and your benefits administrator uses that letter to decide if the expense qualifies.

The IRS sets the rules for what counts as a medical expense (there are thousands of qualified items and services), but not everything is crystal clear. An LMN helps move an item from the “maybe not” pile into the “approved” pile.

Why Does an LMN Matter?

FSAs use pre‑tax dollars, which means you’re not paying income taxes on that money. The tax savings are great, but it also means there are rules.

Some items that help your health don’t automatically qualify for FSA reimbursement. Without an LMN, these expenses are usually denied:

• Special dietary foods (like gluten‑free products for celiac disease)
• Exercise equipment prescribed for a medical condition
• Air purifiers or humidifiers for respiratory issues
• Compression socks beyond basic over‑the‑counter versions
• Massage therapy for a diagnosed condition
• Wigs due to medical hair loss

With a valid LMN, those same expenses may become eligible. That translates to more flexibility, less out‑of‑pocket cost, and a happier wallet.

What Does a Good LMN Need to Include?

Not all letters are created equal. A quick note that says “this helps the patient” probably won’t cut it.

A solid Letter of Medical Necessity usually includes:

• Patient information – The name of the person receiving treatment
• Provider information – The provider’s name, credentials, and contact details
• Diagnosis or condition – The specific medical issue being treated (bonus points for an ICD‑10 code)
• Item or service description – Exactly what’s being recommended and how it’s used
• Medical explanation – Why this item is necessary for this condition
• Duration of need – Short‑term, long‑term, or ongoing
• Signature and date – No signature = no approval

Basically, the letter should clearly answer: What is this? Why is it needed? And for how long?

A Few Things to Keep in Mind

Even with an LMN, reimbursement isn’t guaranteed. Your FSA administrator still makes the final call based on IRS rules. When in doubt, it’s smart to check before buying.

Also, LMNs usually need to be renewed every year. That letter from three years ago? Probably expired (kind of like milk, but less smelly).

And finally: save everything. Keep the letter, receipts, and any emails just in case questions come up later. Future you will be glad you did.

Letter of Medical Necessity: The Final Word

Stop thinking about the Letter of Medical Necessity as red tape and start viewing it as a useful tool. It helps make sure FSA money is used correctly and allows you to get reimbursed for more legitimate medical needs.

If your healthcare provider recommends something and you think it should qualify, ask about an LMN. It’s a small step that can lead to real savings.

Your bank account will appreciate it.

Captain Contributor is an award-winning employee education and engagement program sponsored by DataPath and used by third party administrators. Contact DataPath today for more information about this program and how you can use it.