503A vs 503B: How US Compounding Pathways Differ
503A and 503B are two sections of the federal Food, Drug, and Cosmetic Act. Each creates a different legal pathway for making compounded drugs — with different prescription rules, regulators, and quality standards.
The short answer
A 503A pharmacy is a state-licensed pharmacy that compounds a drug for an identified individual patient under a patient-specific prescription. A 503B outsourcing facility is an FDA-registered facility that compounds drugs under federal manufacturing-style oversight and may distribute them without patient-specific prescriptions, subject to statutory conditions. The numbers are statute sections — 21 U.S.C. §353a and §353b — not quality grades.
| Dimension | 503A pharmacy | 503B outsourcing facility |
|---|---|---|
| Legal basis | FD&C Act §503A (21 U.S.C. §353a) — longstanding pharmacy compounding exemption | FD&C Act §503B (21 U.S.C. §353b) — category created by the Drug Quality and Security Act of 2013 |
| Prescription | Requires a valid prescription for an identified individual patient | May compound without patient-specific prescriptions, subject to conditions in §503B |
| Primary regulator | State board of pharmacy | FDA (registration, inspection) alongside state licensing where applicable |
| Registration | State pharmacy license; no FDA registration required by §503A | Must register with FDA as an outsourcing facility |
| Quality standard | USP compounding standards (<795> non-sterile, <797> sterile) as state law adopts them | Current Good Manufacturing Practice (CGMP) — the federal manufacturing standard |
| Inspection | State board inspection | FDA inspection on a risk-based schedule |
| Bulk substances | Compounded from substances that meet a USP/NF monograph, appear on an FDA-recognized list for 503A, or satisfy other statutory conditions | Generally limited to substances on FDA's 503B bulks list or meeting other §503B conditions |
| Copies of approved drugs | Restricted — with narrow statutory exceptions | Restricted — with narrow statutory exceptions |
How to tell which pathway made a compound
- Ask the dispensing pharmacy directly. A pharmacy can hold both kinds of operation, but a given product is made under one pathway.
- Check the FDA registration list. 503B outsourcing facilities appear on FDA's official list of registered outsourcing facilities. If the operation is not on it, it is not a registered 503B.
- Check the state license. A 503A pharmacy's license standing lives in its state board of pharmacy records. There is no single federal registry of state licenses.
Our facility lookup routes any name to these primary sources.
What the difference does not mean
- 503A is not "unregulated" — it is regulated primarily by the state, under federal conditions set by §503A.
- 503B registration is not an FDA approval of any compounded drug. Compounded drugs are not FDA-approved products.
- Neither pathway says anything about whether a specific compound is appropriate for a specific person — that is a clinical question outside this registry's scope.
Sources
Information only. Not medical or legal advice. Statutory summaries do not restate every condition; read the linked primary sources before relying on a pathway determination.