503A vs. 503B Compounding Pharmacies Explained

If your prescriber mentions a "compounded" medication, you may hear the terms 503A and 503B. These numbers come from two sections of the federal Food, Drug, and Cosmetic Act, and they describe two very different kinds of compounders. This guide explains the difference in plain English so you can ask better questions. It is general information, not legal advice.

Key takeaways

• 503A covers traditional, state-licensed pharmacies that compound medicine for a specific patient based on a prescription.
• 503B covers "outsourcing facilities" that register with FDA, follow federal manufacturing quality rules (CGMP), and can make larger batches.
• Neither type of compounded drug is FDA-approved. FDA does not review compounded drugs for safety or effectiveness before they are sold.
• Compounding rules for GLP-1 drugs tightened after FDA declared the semaglutide and tirzepatide shortages over, and FDA has proposed more limits in 2026.
• You can look up a pharmacy's state license and check FDA's public list of registered outsourcing facilities.

What compounding is, and why it exists

Compounding means a pharmacist combines, mixes or changes ingredients to make a medicine for a patient whose needs aren't met by an approved product. Classic examples include a liquid version of a pill for a child, or a version without a dye someone is allergic to.

Compounded drugs can fill real gaps. They also skip the FDA approval process, which is why the law puts conditions on who can compound, what they can use, and how. For a broader look at how this applies to GLP-1s, see our post on brand-name vs. compounded GLP-1s.

503A pharmacies: the traditional model

A 503A pharmacy is the kind of compounding pharmacy most people picture. It is licensed by a state board of pharmacy, and the state is its main day-to-day regulator.

Key features:

• Patient-specific prescriptions. 503A compounding is generally done for an identified patient based on a valid prescription.
• State oversight first. State boards license and inspect these pharmacies. FDA can inspect too, often for cause or after complaints, and may refer findings to the state.
• Limited exemptions. When a 503A pharmacy follows the section's conditions, its compounded drugs are exempt from three federal requirements: FDA approval, full labeling with directions for use, and federal CGMP manufacturing rules. Other parts of the law still apply, including the ban on making drugs under insanitary conditions.
• Ingredient limits. A 503A pharmacy can only compound from bulk ingredients that meet certain tests, such as being part of an FDA-approved drug, having a USP monograph, or appearing on FDA's 503A bulks list. We cover that list in FDA bulk drug substance categories explained.
• No "essential copies." 503A pharmacies generally may not regularly compound drugs that are essentially copies of a commercially available FDA-approved drug.

503B outsourcing facilities: the larger-scale model

Section 503B was added in 2013 after a deadly fungal meningitis outbreak was traced to contaminated compounded injections. It created a voluntary category called the outsourcing facility.

Key features:

• FDA registration. The facility must register with FDA and re-register each year.
• CGMP applies. Unlike 503A pharmacies, outsourcing facilities must follow federal current good manufacturing practice rules.
• Routine FDA inspections on a risk-based schedule, plus adverse event reporting and reports to FDA on the products they make.
• Batches without individual prescriptions. Outsourcing facilities can make drugs in advance, often for hospitals, clinics and doctors' offices to keep on hand.
• Their own bulk rules. They can compound from bulk substances only if the drug is on FDA's drug shortage list or the substance is on the separate 503B bulks list for "clinical need."

FDA has said that because outsourcing facilities are held to CGMP and routine inspections, purchasers who need compounded drugs should consider them.

Side-by-side comparison

What changed for compounded GLP-1s

During the national shortages of semaglutide and tirzepatide, compounders were allowed more room to make these drugs. That changed once FDA declared the shortages resolved:

• Tirzepatide: FDA declared the shortage resolved in December 2024, with wind-down periods for compounders that ended in early 2025.
• Semaglutide: FDA declared the shortage resolved on February 21, 2025. The wind-down ended April 22, 2025 for 503A pharmacies and May 22, 2025 for 503B outsourcing facilities.

In 2026, FDA went further. On March 3, 2026, it sent warning letters to 30 telehealth companies over marketing that suggested compounded GLP-1s were the same as approved products. On April 30, 2026, FDA proposed excluding semaglutide, tirzepatide and liraglutide from the 503B bulks list, which would keep outsourcing facilities from compounding them from bulk ingredients. As of this writing, that proposal had gone through public comment, and you should check FDA for its final status.

Narrow 503A situations can still come up, for example when a prescriber documents that a patient needs a change the approved product can't provide. Those decisions belong to your prescriber and pharmacist, not to a website.

How to check a compounder

You don't need to be an expert to do a few quick checks:

1. Ask which type it is. A legitimate pharmacy will tell you if it is a 503A pharmacy or a 503B outsourcing facility.
2. Verify the state license. Look up the pharmacy on your state board of pharmacy's website. NABP keeps a directory of state boards.
3. Check FDA's outsourcing facility list. FDA publishes a table of registered 503B facilities with inspection dates and whether a Form 483 was issued.
4. Ask about testing and the label. Ask what the product contains, how it was tested, and the beyond-use date.
5. Be wary of "same as brand" claims. Compounded drugs are not FDA-approved and are not the same as the brand product.

Our telehealth page has more questions to ask, and the PepSteady app lets you record your pharmacy and prescription details in one place.

The bottom line

503A pharmacies compound for individual patients under state oversight, while 503B outsourcing facilities register with FDA and follow federal manufacturing rules. Neither produces FDA-approved drugs. Rules for compounded GLP-1s have tightened since 2025, so ask your prescriber and pharmacist how the current rules apply to your situation.

Sources

• FDA: Compounding Inspections and Oversight FAQ
• FDA: Registered Outsourcing Facilities
• FDA: Clarifies Policies for Compounders as National GLP-1 Supply Begins to Stabilize
• FDA: Proposal to exclude semaglutide, tirzepatide and liraglutide from the 503B bulks list
• Drug Topics: FDA warns 30 telehealth companies over compounded GLP-1 marketing (March 2026)

Frequently asked questions