503A vs 503B: the two kinds of compounding pharmacy

If you are taking a compounded medication, it came from one of two categories, and they are not equivalent. The names come from the sections of federal law that create them, sections 503A and 503B of the Federal Food, Drug, and Cosmetic Act, added by the Drug Quality and Security Act of 2013.

Knowing which one made your medicine tells you what oversight sat behind it.

Section 503A: the traditional compounding pharmacy

A state licensed pharmacy or physician, compounding a medicine for an individual patient with a prescription.

• Regulated primarily by the state board of pharmacy.
• Compounds patient by patient. It is not supposed to be making batches for stock.
• Not required to follow federal manufacturing quality rules.
• Does not register with the FDA as an outsourcing facility.

This is the pharmacy that makes a liquid version for a child who cannot swallow a pill, or leaves out a dye someone reacts to. It is the older and more common category.

Section 503B: the outsourcing facility

A facility that registers with the FDA as an outsourcing facility.

• May compound in batches, without a prescription for a named individual.
• Must follow current good manufacturing practice, the federal quality rules that apply to drug manufacturing.
• Subject to FDA inspection.
• Must report adverse events to the FDA.

This category was created after a 2012 fungal meningitis outbreak traced to a compounding pharmacy that was operating at industrial scale under rules written for small scale work. 503B exists to put scale under federal oversight.

The thing both categories have in common

Neither produces an FDA approved drug. Registration is not approval. Inspection is not approval. A 503B facility making a compounded product is not making an approved medicine, and the FDA has said so directly: compounding facilities "are not 'FDA-approved' or 'FDA-licensed' entities."

If a website describes its source as an FDA approved or FDA licensed pharmacy, that is one of the specific claims the FDA has told telehealth companies not to make.

The rule that limits both

Neither category may compound something that is essentially a copy of a commercially available FDA approved drug. This is the central restriction, and it exists so compounding fills genuine individual needs rather than producing cheaper versions of approved medicines.

There is one large exception. While an approved drug is on the FDA's shortage list, the restriction is relaxed.

That exception is why compounded GLP-1s appeared at scale, and the different deadlines that applied to each category when the shortages ended are why the two categories are worth understanding.

How the deadlines differed

When the FDA determined the shortages were resolved, it gave the two categories different windows.

503B facilities consistently got an extra thirty days, which reflects that batch production cannot be stopped as abruptly as patient by patient compounding.

In May 2026 the FDA proposed going further for 503B facilities specifically, by removing semaglutide, tirzepatide and liraglutide from the list of bulk substances those facilities may compound from at all, on the basis that there is no clinical need.

How to find out which one you are dealing with

Ask, directly: which pharmacy or facility compounds this, and are they registered with the FDA as an outsourcing facility?

A provider who cannot answer that quickly is telling you something. The FDA publishes a list of registered outsourcing facilities, and state boards of pharmacy publish licence lookups for pharmacies in their state.

Be aware of one specific pattern the FDA has flagged: branding that implies the telehealth company itself made the drug. If the company's own name is on the vial with no mention of a compounder, ask who actually made it.

What to ask

• Which pharmacy or facility compounds my medication?
• Are they a 503A pharmacy or a registered 503B outsourcing facility?
• Are they licensed in my state, and can I look that up?
• Whose name is on the label, and is that the compounder or the seller?

Sources

• Federal Food, Drug, and Cosmetic Act sections 503A and 503B, 21 U.S.C. 353a and 21 U.S.C. 353b
• Drug Quality and Security Act, Public Law 113-54 (2013)
• The "essentially a copy" restriction, 21 U.S.C. 353a(b)(1)(D) and 21 U.S.C. 353b(a)(5)
• FDA, "FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize"
• FDA, "FDA to Telehealth Companies: What to Know When Promoting Compounded Drugs"
• FDA, "FDA Proposes to Exclude Semaglutide, Tirzepatide, and Liraglutide on 503B Bulks List"; Federal Register document 2026-08552

How we verify: see /how-we-verify.

Keep reading

How to check whether a provider is legitimate, at /guides/how-to-check-a-telehealth-provider.

Whether you can still get compounded semaglutide, at /guides/can-i-still-get-compounded-semaglutide.