How to Get a Letter of Medical Necessity for a Gluten-Free Diet (+ Template)
The one piece of paperwork that unlocks FSA, HSA, and tax reimbursement for the gluten-free "tax": what it is, who writes it, how to ask, and a template your doctor can sign in 30 seconds.
Note: I'm a person living with celiac disease, not a tax professional or physician. This is general information, not medical or tax advice. Your doctor and your plan administrator have the final say.
What a Letter of Medical Necessity actually is
A Letter of Medical Necessity (LMN) is a short note from your doctor stating that a treatment (in this case, a gluten-free diet) is medically required to treat a diagnosed condition. For households managing celiac disease, it's the document that turns "gluten-free food is expensive" into "the extra cost is a reimbursable medical expense."
It's the single thing most people get stuck on. It shouldn't be: it's one paragraph, and you can hand your doctor a draft to sign.
Why you need one
To claim the gluten-free price premium through an FSA, HSA, or as a tax deduction, the IRS wants the medical need substantiated by a physician (per IRS Publication 502 and Revenue Ruling 55-261). The LMN is that substantiation. Without it, the claim isn't supported. With it, you're documenting exactly what the rules ask for.
- FSA: most administrators want the LMN on file (often once per plan year) plus your receipts.
- HSA: you self-reimburse, but keep the LMN with your records in case of an audit.
- Tax (Schedule A): keep it with your tax records; some people attach a copy.
Who can write it
Any treating physician who knows your diagnosis, usually your gastroenterologist or your primary care provider. If a celiac disease diagnosis is in your chart, either can write it. You do not need a specialist visit just for this; it can ride along with a normal appointment or go through your patient portal.
The template (copy, paste, hand to your doctor)
[Doctor's letterhead]
Re: Letter of Medical Necessity: Gluten-Free Diet Patient: [Your name] DOB: [Date] Date: [Date]
[Patient name] has been diagnosed with celiac disease (ICD-10: K90.0). A strict, lifelong gluten-free diet is medically necessary to treat this condition; there is no pharmaceutical alternative or substitute treatment. Gluten-free foods are required to manage the patient's diagnosis and typically cost significantly more than their conventional gluten-containing equivalents.
I am prescribing the gluten-free diet as medical treatment and request that the incremental cost of gluten-free foods be considered an eligible medical expense for the purposes of the patient's HSA/FSA and/or medical expense deduction.
This letter is valid for the [current tax/plan year / duration of treatment].
Sincerely, [Physician name] · [Signature] · [NPI #] · [Date]
Tweaks:
- If your diagnosis is non-celiac gluten sensitivity or a wheat allergy, swap the condition + ICD-10 code (your doctor will know it).
- For dermatitis herpetiformis (the skin form of celiac disease), name that diagnosis.
- Ask your doctor to phrase it as "prescribing" / "medically necessary". That language matters.
How to ask your doctor (so it actually happens)
- Message through the patient portal or bring it to your next visit.
- Say: "For my celiac disease diagnosis, I need a short Letter of Medical Necessity for my FSA/HSA so I can claim the extra cost of gluten-free food. I've drafted one on your letterhead. Would you review and sign it?"
- Hand them the template. Most will sign as-is or tweak a line.
- Ask: "How often will I need this renewed?" Answers vary by administrator (some once, some annually).
How often to renew it
It depends on your pathway/administrator:
- Some FSA administrators accept it once; others want it annually.
- A few accept "duration of treatment" wording (celiac disease is lifelong) so it doesn't expire.
- For HSA/tax records, keep a current copy with each year's receipts.
When in doubt, get one dated for the current year. It covers you everywhere.
Common questions
Does it have to say "prescription"? It should read as the doctor prescribing or deeming the diet medically necessary. "I recommend a gluten-free diet" is weaker than "a gluten-free diet is medically necessary to treat this diagnosis."
Can I write it myself and have them sign? Yes. That's exactly what the template is for. The doctor reviews and signs; that's what makes it valid.
What if my doctor won't? It's a routine request for a documented celiac disease diagnosis. If a PCP hesitates, your GI (who made the diagnosis) is the natural person to ask.
Do I need a new letter for each receipt? No. The LMN covers the medical need; your receipts document the spend. One current LMN plus your receipts is the package.
Once you have the LMN
You're ready to claim. The remaining work is identifying the gluten-free items on each receipt, finding the comparable regular product, and calculating the per-ounce excess cost, then packaging it for your FSA/HSA. That last part is the tedious bit, and it's exactly what GF Savings automates: upload a receipt, it finds the GF items, does the excess-cost math, and produces a submission-ready PDF. The first receipt is free.
Start with the letter. It's the one step that unlocks everything else, and it's a single paragraph away.
Related reading
- Can I claim gluten-free food on my FSA? The complete guide
- Gluten-free HSA reimbursement: how to pay yourself back
Sources
- IRS Publication 502 (Medical and Dental Expenses): https://www.irs.gov/publications/p502
- Celiac Disease Foundation, Tax Deductions: https://celiac.org/gluten-free-living/federal-benefits/tax-deductions/
- Beyond Celiac, Tax Deduction Guide: https://www.beyondceliac.org/gluten-free-diet/shopping/tax-deduction-guide/