What Is a Letter of Medical Necessity (LMN) — And How It Unlocks Your HSA

There’s a powerful document many HSA users haven’t discovered yet — and it can help you use your HSA more intentionally across your health, fitness, and everyday wellness needs.

It’s called a Letter of Medical Necessity (LMN).

It's not complicated, but it does change how certain HSA expenses are evaluated. With an LMN, you may be able to use your HSA funds for items that aren't automatically HSA-eligible — opening the door to a much wider range of qualifying purchases.

This guide covers what an LMN is, who can write one, how to get one, and where it actually makes a difference.

What Is a Letter of Medical Necessity?

A Letter of Medical Necessity (LMN) is documentation from a licensed healthcare provider that connects a specific product or service to a diagnosed medical condition.

It's what bridges the gap between "general wellness" and "medically necessary" — and that distinction matters a lot when it comes to your HSA. General wellness items (outside of the IRS's list of automatically eligible items) aren't HSA-eligible expenses, but medically necessary expenses are covered.

Under IRS Section 213(d), eligible medical expenses must be for the "diagnosis, cure, mitigation, treatment, or prevention of disease." In short, an LMN is how you make that connection for items that wouldn't otherwise qualify.

A simple example:

• Without an LMN → Iron Supplement = general wellness (not eligible)

• With an LMN tied to a documented deficiency → potentially HSA-eligible

Same product. Different classification. That's the power of an LMN.

Sources:

• IRS Publication 502

• IRS Code §213(d)

What an LMN Can Cover (With Limits)

As mentioned, an LMN may support expenses that are not automatically eligible, but only if they are clearly tied to a medical condition.

Common categories where LMNs are used:

• Supplements (for diagnosed deficiencies)

• Certain medical-grade devices

• Sleep-related tools (if tied to a condition)

• Some fitness or therapy-related expenses

  
  

Who Can Write an LMN

An LMN must be issued by a licensed provider authorized to diagnose and treat. Always ensure the provider is licensed in your state.

Typically accepted:

• MD / DO

• Nurse Practitioner (NP)

• Physician Assistant (PA)

• Licensed mental health professionals

• Registered dietitians (for nutrition-related conditions)

• Chiropractors (for musculoskeletal issues)

Not accepted:

• Unlicensed health coaches, personal trainers, or wellness providers

Source:

• IRS Publication 502 (qualified medical expenses must be for diagnosis/treatment of disease and typically require services from legally authorized healthcare providers; does not provide a fixed provider list)

What a Proper LMN Should Include

The letter itself typically explains:

• Your medical condition

• Why a specific product or service is needed

• How it treats or manages that condition

Ask your doctor or a qualified healthcare provider for guidance on their preferred format. Here is an example of what a strong LMN should clearly document:

Patient Info

• Name

• Date of birth

Provider Info

• Name and credentials

• License number

• Signature

Medical Justification

• Diagnosed condition

• Explanation of need

• How the item helps

Product Scope

• Specific product or category

• Duration (often ~12 months)

Two Ways to Get an LMN

1. Through Your Doctor: This is the most traditional route. Best when:

• You have an existing diagnosis

• Your doctor knows your history

• The item is clearly tied to treatment

How to approach it:

“I’m managing [condition], and I believe [product] would help. Would you be able to provide a Letter of Medical Necessity?”

Simple, direct, and usually quick.

2. Through a Telehealth Provider (e.g., Truemed, Burst, Flex): Some platforms connect you with a clinician who reviews your health information and may issue an LMN if they determine you have an appropriate health necessity. Learn more about Truemed here.

Typical flow:

1. Complete intake

2. Clinician review

3. LMN is issued if the criteria are met

This can be faster, but it still relies on a legitimate medical condition and approval.

How Long an LMN Lasts

Most LMNs are valid for 12 months.

During that time:

• Multiple purchases may be covered

• Renewal is typically required annually

An LMN typically applies to a product type tied to a condition — not necessarily to a single transaction.

That means:

• You may be able to use the same LMN across multiple purchases for the valid period.

• Potentially from different retailers if the retailer is not specified in the LMN.

How to Use an LMN for Purchases

1. Get your LMN first: Make sure it clearly connects your condition to the product or category.

2. Make your purchase:

   • Use your HSA card (if your administrator allows), or

   • Pay with a personal card and plan to reimburse yourself

3. Choose your reimbursement timing:

   • Reimburse yourself right away, or

   • Keep your receipt + LMN on file and reimburse later to allow your HSA investments to continue growing

Maintain documentation for at least 3 years, preferably 7, in case of an audit. Seek advice from a tax professional for further clarification based on your tax situation.

Sources:

• IRS Publication 969

• IRS Notice 2004-50

Common Mistakes to Avoid

Here are some common mistakes:

Using your HSA for general wellness instead of medical need: To qualify as an eligible expense, the expense must relate to the diagnosis, cure, mitigation, treatment, or prevention of a specific disease or condition under IRC Section 213(d). If the underlying purpose is general wellness or fitness, an LMN will not change that.

Missing receipts or incomplete documentation: An LMN alone isn't enough. You need to keep the LMN, the receipt, and any supporting documentation together — and hold onto them for at least 3 years, preferably 7, in case of an audit. No receipt means no proof that the expense was legitimate, even if the LMN is solid.

Using an unqualified provider: The LMN must come from a licensed healthcare provider who is authorized to diagnose and treat — not a wellness coach, personal trainer, or unlicensed practitioner. If the provider isn't qualified, the letter won't hold up.

Assuming approval is automatic: An LMN improves your case, but it does not guarantee approval. The item still needs to meet IRS criteria, and your documentation needs to be complete.

The Bigger Picture

An LMN is not a loophole.

It’s a documentation tool recognized by the IRS — but it only works when:

• The condition is legitimate

• The treatment is appropriate

• The documentation is accurate

Used correctly, it can expand how you use your HSA — especially for expenses that sit between “medical” and “wellness.”

It's Your Turn

Think about the last three to six months of health purchases you made out of pocket.

Supplements. A fitness tracker. Exercise equipment. Shoes. Pillows.

How many of those could have been covered with pre-tax HSA dollars — with or without a Letter of Medical Necessity?

For most people, the answer is more than they expect.

Talk to your doctor or visit a telehealth provider to see what you qualify for.

Real savings on purchases you are already making. That's saving wiser.

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Thank you for reading, The Save Wiser Team

This content is for informational purposes only and does not constitute tax, legal, financial, or medical advice. We make every effort to verify the accuracy of the information provided; however, HSA eligibility rules and IRS guidelines can and do change. For questions about HSA eligibility, refer to IRS Publication 502 and IRS Publication 969 directly, or consult a licensed tax professional, financial advisor, or qualified healthcare provider.