Why can't I get a Letter of Medical Necessity for my auto-substantiated product?

Last updated: February 18, 2026

If you've requested a Letter of Medical Necessity (LOMN) for your purchase and were told that one cannot be provided, it's likely because your item is classified by the IRS as "auto-substantiated."

Understanding IRS Product Classifications

The IRS recognizes two main categories of HSA/FSA eligible products:

  • Dual-purpose items — Products that have both cosmetic and medical uses. These require a LOMN to confirm the product is being used for medical purposes.

  • Auto-substantiated items — Products with only medical use, which are automatically considered eligible without requiring additional documentation.

Why Flex Cannot Provide LOMNs for Auto-Substantiated Products

Because auto-substantiated items are automatically recognized as medically eligible by the IRS, Flex's system is not set up to generate Letters of Medical Necessity for these products. The itemized receipt you received is all the documentation you need to keep for your records for tax or reimbursement purposes.

What to Do If Your FSA/HSA Administrator Still Requires a LOMN

Some FSA and HSA administrators have their own internal policies that may still require a LOMN even for auto-substantiated products. This is particularly common with employer-sponsored FSAs, which tend to have stricter requirements than HSAs.

If your administrator continues to require a LOMN despite the product being auto-substantiated:

  1. Contact your FSA/HSA administrator directly and explain that the product falls under an IRS auto-substantiated category

  2. Reference the IRS classification in your appeal to show the product shouldn't require additional documentation

  3. Consult with your healthcare provider if your administrator absolutely requires a letter from a medical professional

Alternative Options

If your FSA/HSA administrator will not accept the auto-substantiated classification and you cannot obtain the required documentation:

  • You may be able to claim the expense on your taxes as a medical deduction

  • Contact the original retailer directly to inquire about returns or cancellations

Unfortunately, this situation is outside of what Flex is able to assist with, as it relates to your specific administrator's internal policies rather than IRS requirements.