What's the Difference Between a Letter of Medical Necessity (LMN) and a Prescription (Rx)?
Learn the key differences between an LMN and an Rx - both are doctor's notes, but when it comes to what they're used for, they're quite different.
2 minute read
What's The Difference Between a Letter of Medical Necessity (LMN) and a Prescription (Rx)?
If you use a Health Savings Account (HSA) or a Flexible Spending Account (FSA), you've likely come across two key documents that can impact whether an expense is reimbursable: a Letter of Medical Necessity (LMN) and a Prescription (Rx). While both may come from a licensed medical provider, they serve different purposes. Below is a quick overview to help you understand the distinction, along with references to official IRS guidelines.
What Is a Letter of Medical Necessity (LMN)?
Definition: An LMN is a written statement from a healthcare professional (e.g., doctor, nurse practitioner) that explains why a particular item or service is medically necessary for treating or managing a specific health condition.
Purpose:
Justifies Non-Standard Items: You might need an LMN for expenses that aren't clearly or traditionally categorized as medical (e.g., nutritional supplements for a diagnosed deficiency, massage therapy for chronic pain, specialized equipment).
IRS Requirement: The LMN helps prove to your FSA/HSA administrator—and potentially the IRS—that the purchase or service is medically essential, rather than for general health or personal comfort.
For more details on which items or services might require an LMN, check out IRS Publication 502 (Medical and Dental Expenses) and Publication 969 (Health Savings Accounts and Other Tax-Favored Health Plans).
Pro Tip If you want to get an LMN same-day, request one for any product or service at app.getburst.com/request-lmn.
Pro Tip: Shopping with Burst's partner merchants at getburst.com/shop can help automate the LMN process. Our partners handle LMN requirements automatically, so you can focus on your health needs rather than paperwork.
What Is a Prescription (Rx)?
Definition: A prescription (Rx) is a written or electronic order from a licensed healthcare provider indicating that a specific medication (or medical device) is required to treat a condition.
Purpose:
Pharmacy Fulfillment: An Rx is typically required to dispense prescription medication at a pharmacy.
IRS Requirement for Certain OTC Medications: Since 2020, many over-the-counter (OTC) medications no longer require an Rx for FSA/HSA reimbursement; however, some plans or specific items may still need an Rx if they're not clearly covered under current guidelines (for instance, some specialized OTC drugs or medical devices).
Key Differences
Aspect | Letter of Medical Necessity (LMN) | Prescription (Rx) |
|---|---|---|
Primary Function | Proves medical necessity for non-traditional items | Authorizes dispensing of medication |
Typical Use Cases | Nutritional supplements, massage therapy, special equipment | Antibiotics, blood pressure meds, insulin, etc. |
Documentation Required | Detailed explanation of condition & necessity | Medical order for a specific drug/device |
Who Issues It | Licensed medical provider (e.g., doctor, NP, therapist) | Licensed medical provider (doctor, NP, PA) |
IRS Compliance | Demonstrates expense is for diagnosis, treatment, or prevention | Often needed for certain OTC items or restricted medications |
When You Might Need Both
In some cases, you may need both an LMN and a prescription. For example:
Medical Foods or Specialized Supplements: You might need an Rx and an LMN to show that the item is required for a particular medical condition (e.g., a specialized formula for someone with a metabolic disorder).
Adaptive Equipment with Prescription-Strength Components: Certain items (like a medical-grade knee brace) might require a prescription to purchase plus an LMN to document necessity for FSA/HSA reimbursement.
How to Quickly Get an LMN
If you're unsure whether you need an LMN or a prescription for a particular item, you can:
Check Official Guidelines: Refer to IRS Publication 502 and Publication 969.
Request an LMN: You can request an LMN for any product or service at app.getburst.com/request-lmn.
Shop with Burst Partners: Browse FSA/HSA-eligible items at getburst.com/shop where many of our partner merchants handle LMN requirements automatically, simplifying the documentation process for you.
In Summary
An LMN provides proof that a non-standard or borderline expense is medically necessary.
A Prescription (Rx) is a direct medical order typically needed to dispense medications or certain medical devices.
Both documents come from licensed medical professionals but serve different roles in confirming eligibility under FSA/HSA guidelines.
If you have unique questions or complex scenarios (e.g., specialized treatments or equipment), consult your healthcare provider, your FSA/HSA administrator, or a tax professional to ensure proper compliance and documentation.
