Quick answer: A Letter of Medical Necessity (LMN) is a document from a licensed healthcare provider that says a specific product or service is medically necessary for you. It's what makes wellness products like gym memberships, fitness trackers, supplements, saunas, cold plunges, yoga studios, massages, and more eligible for HSA/FSA reimbursement.

The IRS has rules about what you can use your HSA/FSA funds for. Most everyday medical expenses (prescriptions, doctor visits, dental work) are automatically eligible. But wellness products - things like a gym membership, a yoga studio, an Apple Watch, supplements, saunas, cold plunges, and much more - fall into a gray area. The IRS calls these "dual-purpose" items because they could be for general wellness or for a specific health need.

An LMN bridges that gap. It's a document from a healthcare provider saying: "This person has [specific health condition], and [this product] is medically necessary to help prevent, manage, or reverse that condition."

With an LMN, those wellness products become eligible for your HSA/FSA funds - saving you 25-40% because you're using pre-tax dollars.

A typical LMN from Crates Health includes:

Your LMN is issued by a licensed healthcare provider (MD, DO, PA, NP) on our team. All are qualified to assess medical necessity and issue LMNs under IRS regulations.

A doctor recommending that you "get more exercise" or "take vitamin D" isn't enough for IRS purposes. An LMN is a formal medical document that specifically:

A general recommendation doesn't check all those boxes. An LMN does.

LMNs are typically valid for 12 months from the date of issuance. After that, you'll need a renewal. If you're on a Crates subscription plan, we handle renewals for you.

Do I need a separate LMN for each product? Yes. Each LMN is tied to a specific product that helps prevent, manage, or reverse a specific health condition. So you'll need a separate LMN for each individual product you're planning to use your HSA or FSA on.

Can my own doctor write an LMN instead? Yes, any licensed healthcare provider can write an LMN. Many customers use Crates because it's faster and easier than scheduling a doctor's appointment, and we also help with reimbursements and navigating potential claim denials. But your personal doctor can absolutely write one too.

Does the LMN need to be dated before my purchase? Yes. Your LMN must be dated on or before the date of the purchase you're trying to get reimbursed for. Backdating LMNs is against IRS policy and is never possible — you must have your LMN before making the purchase for products that require one.

What conditions qualify for an LMN? A wide range of conditions qualify, including obesity, hypertension, Type 2 diabetes, high cholesterol, depression, anxiety, chronic pain, sleep disorders, and many more. The key is that the product needs to connect to a specific health need, not just general wellness. Our health assessment helps identify which conditions apply to you.

Is this legal? Yes. LMNs are an established mechanism under IRS rules (Publication 502) for qualifying dual-purpose items as medical expenses. This is exactly how the IRS intends the system to work - a licensed provider determines medical necessity, and you get to use your pre-tax health funds accordingly. There are years and years of precedent from the IRS accepting LMNs, making this a widely established practice.

Will my employer see my LMN? No. Your LMN is between you and your HSA/FSA admin (and the IRS, if they ever decide to audit you — which they have the right to do up to 10 years after a transaction). Your employer does not see your medical documentation.

If you have questions about your LMN, chat with us or email [email protected]. We're happy to help.