503A Pharmacies vs 503B Outsourcing Facilities: What the Letters Mean for Your Prescription

Quick answer

The short version, as of September 2026: a 503A pharmacy prepares a compounded medication for a named patient, in the statute's words "for an identified individual patient based on the receipt of a valid prescription order," under the day-to-day oversight of a state board of pharmacy. A 503B outsourcing facility is a separate federal category created by a law signed on November 27, 2013: it registers directly with the FDA, compounds sterile drugs under current good manufacturing practice (CGMP), may work with or without a prescription for each patient, and, again in the statute's words, "is not required to be a licensed pharmacy." Neither one produces an FDA-approved drug. The FDA's public table of registered outsourcing facilities, updated as of September 8, 2026, lists 96 of them; 503A pharmacies have no federal list.

If you have looked into compounded medications, you have probably met the labels 503A and 503B. They sound like fine print, but they answer a practical question: who is allowed to prepare your medication, under whose oversight, and on what scale.

Where do the names 503A and 503B come from?

Both are section numbers in the Federal Food, Drug, and Cosmetic Act (the FD&C Act), codified at 21 U.S.C. 353a and 21 U.S.C. 353b. Section 503A was added in November 1997. Section 503B came from the Drug Quality and Security Act, Public Law 113-54, which, as the FDA's outsourcing facility page puts it, "created a new section 503B" under which "a compounder can become an outsourcing facility." The same 2013 law also amended 503A.

That history explains the design: 503A keeps the traditional pharmacist, patient and prescriber triangle, while 503B creates a category closer to a drug manufacturer, held to manufacturing quality rules and supervised by the FDA directly.

What does a 503A pharmacy do?

Under section 503A, compounding is done by "a licensed pharmacist in a State licensed pharmacy or a Federal facility," or by "a licensed physician," for a patient whose prescriber has sent a valid prescription order. Key characteristics:

• State oversight first. The FDA's compounding questions and answers say state boards of pharmacy have primary responsibility for day-to-day oversight of these pharmacies, and that the FDA "does conduct surveillance and for-cause inspections" of them too.
• Tied to an identified patient. The one exception is narrow: compounding "in limited quantities" before a prescription arrives, based on a history of valid prescription orders within an established relationship with that patient or prescriber.
• Ingredient standards. Ingredients must meet the applicable United States Pharmacopeia (USP) or National Formulary monograph where one exists, and the USP chapter on pharmacy compounding.
• A limit on copies. No compounding "regularly or in inordinate amounts" of drug products that are "essentially copies of a commercially available drug product."
• A limit on interstate distribution. Either the pharmacy's state has signed a memorandum of understanding with the FDA on interstate distribution, or out-of-state distribution must stay within a small fixed share of total prescription orders that the statute sets.

Not every patient knows who compounded their prescription, though: the FDA cautions that people who buy compounded drugs through online pharmacies and telehealth platforms "may not know the identity of the compounder that produced the drug." Check that your label names the dispensing pharmacy; if it does not, ask.

What does a 503B outsourcing facility do?

The statute defines an outsourcing facility as a facility at one location that compounds sterile drugs, has elected to register as an outsourcing facility, and meets all of section 503B. It "is not required to be a licensed pharmacy," and it "may or may not obtain prescriptions for identified individual patients." Key characteristics:

• Registered with the FDA on electing the status and every year between October 1 and December 31.
• Reports its products to the FDA on registration and each June and December, and reports adverse events.
• Inspected by the FDA on a risk-based schedule that weighs compliance history, recalls, the inherent risk of its drugs, and whether it has been inspected within the last 4 years.
• Follows CGMP. The FDA says outsourcing facilities "must comply with CGMP requirements."
• Carries a specific label, including the statement "This is a compounded drug." (or an FDA-specified alternative), the facility's name, address and phone number, and a lot or batch number.
• Cannot be wholesaled. Only the facility that compounded the drug may sell or transfer it.
• Appears on a public FDA list of registered outsourcing facilities.

Who can receive it: one patient or a clinic's office stock?

A 503A pharmacy compounds for an identified patient, with only the limited anticipatory compounding described above. A 503B outsourcing facility is not limited that way: when its drug goes out other than on a prescription for an individual identified patient, the statute requires the label to say "Office Use Only," and the statute expressly allows administration in a health care setting. That is the route by which a clinic or hospital can keep a compounded sterile drug on hand, something section 503A does not provide for.

503A vs 503B side by side

Why does only 503B have to follow CGMP?

A drug that meets the conditions of section 503A is exempt from three provisions: 21 U.S.C. 351(a)(2)(B), which treats a drug as adulterated when its manufacture does not conform to current good manufacturing practice; 352(f)(1), adequate directions for use on the label; and 355, new drug approval. A drug that meets the conditions of section 503B is exempt from 352(f)(1), 355 and 360eee-1, the drug supply chain requirements, but not from 351(a)(2)(B).

In the FDA's words, outsourcing facility drugs "can qualify for exemptions from FDA approval requirements and the requirement to label products with adequate directions for use, but not from current good manufacturing practice (CGMP) requirements." The federal CGMP regulations for finished pharmaceuticals are in 21 CFR Part 211.

A 503A pharmacy works to a different set of standards: the statute's ingredient rules, the USP compounding chapters (General Chapter 795 for nonsterile and 797 for sterile preparations), and its state board. One rule covers both. "Regardless of where compounding occurs," the FDA says, other federal law applies, "including provisions regarding insanitary conditions."

What can each type compound from? The bulk drug substance lists

A bulk drug substance is the active ingredient in raw form. Under section 503A, the FDA's 503A bulks page lists three routes: a substance that meets a USP or NF monograph; if no monograph exists, a component of an FDA-approved drug; and otherwise, a substance on the 503A bulks list. The FDA's final rule in February 2019 placed six substances on that list.

Under section 503B, the FDA's 503B bulks page allows a bulk substance only if it is on the 503B bulks list, for substances "for which there is a clinical need," or if the drug made from it is on the FDA's drug shortage list at the time of compounding, distribution and dispensing.

Under both, each bulk substance needs a valid certificate of analysis and a manufacturer registered with the FDA under section 510 of the FD&C Act.

What changes when a drug shortage ends?

A shortage relaxes some limits, and its end brings them back, as the FDA's shortage compounding page explains. For a 503A pharmacy, a drug on the shortage list is not considered commercially available, so the copies limit does not apply while the shortage lasts; "all other conditions of section 503A must be met." Once a shortage is resolved, the FDA's GLP-1 statement adds, the FDA "generally considers the drug to be commercially available."

For a 503B outsourcing facility, the shortage list opens the bulk substance route and lifts the bar on identical or nearly identical copies. After a drug leaves the list, the FDA "may take action" if a facility fills new orders, or fills existing orders more than 60 days after removal.

This is where GLP-1 medications come in. The FDA's GLP-1 compounding statement records that the tirzepatide injection shortage was resolved (October 2, 2024, confirmed after re-evaluation on December 19, 2024) and the semaglutide injection shortage on February 21, 2025, with the FDA's temporary enforcement periods ending during 2025. Its April 1, 2026 update states that tirzepatide and semaglutide "do not currently appear on the 503B bulks list or on FDA's drug shortage list," which leaves no bulk substance route open for them under section 503B.

For 503A pharmacies, the same update restates the copies rule: the FDA intends to treat a compounded product as essentially a copy when it has the same active ingredient in the same, similar or easily substitutable strength, by the same route, unless a prescriber documents a change that produces a significant difference for an identified individual patient. In the FDA's example, a product combining semaglutide with vitamin B12 may still be considered essentially a copy when those route and strength tests are met. The FDA also stated that, at this time, it does not intend to act against a compounder that fills four or fewer such prescriptions in a calendar month.

Compounded medications are not FDA-approved as final products. The FDA "recommends patients be prescribed an FDA-approved drug when available and appropriate for the patient." For more, see is compounded semaglutide FDA-approved?

Is a 503B outsourcing facility safer or better than a 503A pharmacy?

A 503B facility carries more federal obligations; a 503A pharmacy sits closer to the patient and prescriber, with the state board as its primary regulator. What they share matters more. The FDA's answer covers both: "Compounded drugs are not FDA-approved. This means that FDA does not verify the safety, effectiveness or quality of compounded drugs before they are marketed." The example of risk the FDA gives turns on practice, not on a section number: "poor compounding practices can result in serious drug quality problems, such as contamination or a drug that contains too much or too little active ingredient." So the useful question is whether this particular compounder is licensed or registered for what it does, and what its record shows.

The comparison that actually matters

The honest answer to "which is better" is that the categories exist for different jobs. For an individual patient with a prescription, the relevant questions are not 503A versus 503B. They are:

1. Is the pharmacy properly licensed for what it does, in the state where you live?
2. Is the pharmacy's identity disclosed to you before dispensing and on the label?
3. Did a licensed clinician evaluate you and decide the medication is appropriate?
4. Does the pharmacy answer questions about its sourcing and quality practices?

A yes to all four is what a careful patient should look for. A provider that hides its pharmacy, or a pharmacy that ships without a prescription, fails this test regardless of which section of the law it claims. Our guide to what a GLP-1 telehealth subscription must tell you looks at the same question from the provider side.

How can you check which kind of facility filled your prescription?

Read the label. A 503B drug must say "This is a compounded drug." and name the outsourcing facility with its address and phone number. Any label should name the dispensing pharmacy. See how to read a prescription label.

Search the FDA's list. The FDA's registered outsourcing facilities table, updated as of September 8, 2026 when we checked it, shows each facility's registration dates, last inspection, whether a Form FDA 483 was issued, whether a recall was conducted, and the action taken. A Form 483 lists investigators' observations and, per the FDA, is not a final agency determination of a violation. The table leaves out state board actions, so check those with the board in the facility's state.

Look up a 503A pharmacy's license. The FDA's BeSafeRx page on locating a state-licensed pharmacy links to every state board's license database, and says: "If your online pharmacy is not listed, you should not use that pharmacy."

Check the website that sells to you. Website certification is a separate layer from pharmacy licensing; our explainer on LegitScript certification describes that program.

Questions to ask before you fill a compounded prescription

• Which pharmacy will prepare my medication, and in which state is it licensed?
• Is it a 503A pharmacy or a 503B outsourcing facility?
• How do I verify its license with the state board of pharmacy, or its registration on the FDA list?
• What should I expect on the label, and whom do I call with a problem?

Any legitimate provider or pharmacy will answer these directly. Hesitation is information.

This article is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider. Compounded medications are not FDA-approved as final products. Medication is prescribed only if a licensed physician determines it is appropriate.