Regulation & News

503A vs 503B Compounding Pharmacies, Explained

Published October 20, 2026 · Last reviewed October 20, 2026 · 6 linked sources · How we source

Nearly every news story about peptides, compounded GLP-1 drugs or "wellness" injections eventually mentions "503A" or "503B." These are sections of the Federal Food, Drug, and Cosmetic Act (FD&C Act) that set out two different ways a compounded drug can be lawfully made in the United States. This guide explains both, side by side, using FDA's own descriptions.

First: what is compounding?

Compounding is the preparation of a drug by combining, mixing or altering ingredients to meet a specific need. The key point for consumers is FDA's plain statement: 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" (FDA Q&A).

FDA also says compounded drugs "should only be used in patients whose medical needs cannot be met by an FDA-approved drug," and warns that poor compounding practices can result in contamination or a drug containing too much or too little active ingredient, which "can lead to serious patient injury and death" (FDA Q&A).

A compounded drug is also not the same as a generic. A generic drug is FDA-approved under section 505(j) and must establish therapeutic equivalence to the brand-name drug; a compounded drug is not approved by FDA (FDA Q&A).

Section 503A: the traditional compounding pharmacy

Section 503A applies to compounding by a licensed pharmacist in a state-licensed pharmacy or federal facility, or by a licensed physician, that is not registered with FDA as an outsourcing facility (FDA). This is the familiar local or specialty compounding pharmacy.

The defining feature is the patient-specific prescription. Under 503A, compounding "must be based on the receipt of a valid prescription for an identified individual patient." It can happen after the prescription arrives, or in limited quantities in advance (FDA).

If all of 503A's conditions are met, the compounded drug is exempt from three federal requirements: current good manufacturing practice (CGMP), labeling with adequate directions for use, and new drug approval (FDA). Day-to-day oversight of these pharmacies falls largely to state boards of pharmacy, but federal law still applies, including provisions on insanitary conditions (FDA Q&A).

Section 503B: the outsourcing facility

Section 503B applies to compounding within an outsourcing facility, a facility registered with FDA under that section. Compounding there is done by or under the direct supervision of a licensed pharmacist, but the facility itself is not required to be a licensed pharmacy (FDA). Section 503B was added to the FD&C Act by the Drug Quality and Security Act (FDA CGMP guidance).

The biggest practical differences:

• No patient-specific prescription required. An outsourcing facility "may or may not obtain prescriptions for identified individual patients" (FDA). That lets 503B facilities produce larger batches, for example for hospitals.
• CGMP applies. Unlike 503A pharmacies, drugs compounded in outsourcing facilities are subject to CGMP requirements (FDA Q&A). FDA has published a dedicated guidance on CGMP for outsourcing facilities (FDA guidance).
• Registration and reporting. Drugs must come from an outsourcing facility that complies with 503B's registration and reporting requirements (FDA).
• Adverse event reporting. Outsourcing facilities must submit adverse event reports to FDA. Section 503A has no explicit equivalent condition (FDA).
• Labeling. 503B labels must carry certain information, including the statement "This is a compounded drug" (FDA).
• No wholesaling. A 503B drug may not be sold or transferred by an entity other than the outsourcing facility that made it, though it can be administered in a health care setting or dispensed under a prescription (FDA).

503B drugs, if all conditions are met, are exempt from labeling with adequate directions for use, new drug approval, and drug supply chain security requirements, but not from CGMP (FDA).

A facility cannot mix the two models casually. FDA guidance states that by registering as an outsourcing facility, an entity elects to have its compounded drugs regulated under 503B, not 503A, and drugs compounded there are not eligible for 503A's exemptions even if 503A's conditions are met (FDA facility definition guidance).

Side-by-side comparison

Source for table: FDA, "FD&C Act Provisions that Apply to Human Drug Compounding". FDA notes its chart is not exhaustive.

The bulk ingredient rules, and why peptides hinge on them

This is where the peptide debate lives. Under 503A, a bulk drug substance must come with a valid certificate of analysis and be made by an FDA-registered establishment. It must also meet one of three tests: comply with an applicable USP or NF monograph; if none exists, be a component of an FDA-approved drug; or, if neither applies, "appear on a list of bulk drug substances that can be used in compounding under section 503A developed by FDA through regulations" (FDA).

Under 503B, the bulk substance must appear on a separate FDA list for 503B, or the finished drug must be on FDA's drug shortage list at the time of compounding, distribution and dispensing (FDA). The shortage route is how compounded versions of some approved drugs became widely available during shortages.

Peptides such as BPC-157 have no USP monograph and are not components of any approved drug. So for a 503A pharmacy to use them lawfully, they would need to be added to the 503A Bulks List through regulations, or FDA would need to adopt an interim enforcement policy. That is exactly what the July 2026 advisory committee votes and the October 2026 interim policy filing are about. See BPC-157 and the FDA and FDA's Interim Peptide Compounding Policy.

FDA's interim policy for nominated bulk substances sorts them into categories while the lists are built. Substances FDA believes "may present significant safety risks" are placed in Category 2 (FDA).

Other limits that apply to both

Both pathways bar compounding drugs that appear on FDA's list of drugs withdrawn or removed from the market for being unsafe or ineffective, and drugs FDA identifies as presenting demonstrable difficulties for compounding. Both also restrict making copies: 503A pharmacies may not regularly compound, or compound in inordinate amounts, drugs that are essentially copies of a commercially available product, and 503B drugs may not be essentially a copy of one or more approved drugs (FDA).

What this means for you

• A "compounded" drug from either pathway is not FDA-approved, and the label "compounded" does not mean "reviewed for safety and effectiveness."
• 503B facilities are held to manufacturing (CGMP) standards and must report adverse events. 503A pharmacies rely more on state oversight and USP compounding standards.
• Neither pathway covers products sold online as "for research use only" or "not for human consumption." Those are outside the compounding system entirely.
• FDA keeps a consumer page on the risks of compounded drugs (FDA). If you are prescribed a compounded drug, it is reasonable to ask your clinician why an approved product will not work and what kind of facility will prepare it.