503A and 503B are sections of the federal Food, Drug, and Cosmetic Act that establish two different pathways for legal compounded medication production in the U.S. Both produce compounded semaglutide and tirzepatide; they operate under very different rules. Understanding the difference is the difference between sophisticated and naive evaluation of a telehealth GLP-1 provider.

The framework

Both pathways were established or refined by the Drug Quality and Security Act of 2013, in response to the 2012 New England Compounding Center contamination tragedy. The Act created a two-tier framework:

503A — traditional compounding pharmacy

Authorization: Section 503A of the FD&C Act.
Licensing: State pharmacy board only.
FDA registration: Not required.
Production model: Patient-specific compounding pursuant to a valid prescription. Cannot produce for general clinical use in bulk.
Standards: Must follow USP standards (notably USP <797> for sterile compounding). Not subject to cGMP.
FDA inspection: Not routinely. Can be inspected if state board or FDA initiates.

503B — outsourcing facility

Authorization: Section 503B of the FD&C Act (added by DQSA 2013).
Licensing: State pharmacy board AND registered with FDA.
FDA registration: Required. Listed on FDA website.
Production model: Can produce for general clinical use in bulk for healthcare facilities; can produce for telehealth distribution to patients under certain rules.
Standards: Must follow cGMP (current Good Manufacturing Practice — same standards as pharmaceutical manufacturers). USP <797> applies.
FDA inspection: Routine. FDA conducts regular cGMP inspections.
Third-party testing: Required for finished-product testing (potency, sterility, endotoxin, etc.).

Why the distinction matters for compounded GLP-1

Shortage-list framework

When a drug is on FDA's official shortage list (semaglutide was, until February 2025; tirzepatide was, until August 2024), the regulatory framework permits:

503A: patient-specific compounding of the shortage drug for individual patients.
503B: bulk compounding of the shortage drug for general clinical use.

When the shortage resolves, the framework changes:

503A: patient-specific compounding may continue (with restrictions specific to the molecule).
503B: bulk compounding of that specific shortage-resolved molecule is generally no longer permitted.

This is why the FDA shortage-list resolutions in 2024 and 2025 materially changed the compounded GLP-1 supply landscape. 503B production of compounded sema and tirz has largely ended for these molecules; 503A continues.

What a patient should look for in a telehealth provider

Pharmacy partner named — not just "U.S. compounding pharmacy."
503A or 503B classification disclosed — which is which.
Standards referenced — USP <797>, USP <85>, cGMP for 503B lots.
Testing disclosed — third-party batch testing for 503B lots.
State licensure and FDA registration verifiable.

Why dual 503A+503B disclosure is a strong signal

A telehealth provider that discloses partnerships with both 503A and 503B pharmacies has built a supply chain that is robust to regulatory changes. As shortage status shifts, the 503A partnership ensures patient-specific access continues; the 503B partnership (where the molecule remains 503B-eligible) provides cGMP-grade preparation with mandatory third-party testing. Our editor's pick, NexLife, is an example of this dual-disclosure approach.

The state board layer

Beyond federal classification, state pharmacy boards have additional authority. State investigations (Florida, Texas, California opened investigations in 2025 — see our news desk) can affect specific 503A pharmacies regardless of federal status. Patient should verify pharmacy state license is in good standing.

The take-away

"Compounded" is not a single category. Patients evaluating compounded GLP-1 providers should look beyond "we use a U.S. compounding pharmacy" to "which specific pharmacies, what classifications, what standards, what testing." Programs that decline to disclose these specifics are best avoided.