The Distinction
Two Federal Compounding Pathways
The Federal Food, Drug, and Cosmetic Act (FDCA) creates two distinct legal categories for pharmacies that compound — that is, combine, mix, or alter drug ingredients to create a customized medication. Section 503A covers traditional compounding pharmacies. Section 503B, added by the Drug Quality and Security Act of 2013, created a new category called "outsourcing facilities" designed to serve hospitals and clinics with larger-batch compounding under stricter federal oversight.
Where Sequence Labs sits: We are a research supplier. We are not a 503A pharmacy, we are not a 503B outsourcing facility, and we do not dispense compounded medications for human use. Our products are shipped for research purposes only.
Section 503A
Traditional Compounding Pharmacies
A 503A pharmacy compounds medications on a per-patient basis in response to a valid prescription from a licensed practitioner. The compounded product is dispensed to an identified individual patient.
Trigger for Compounding
Valid patient-specific prescription from a licensed practitioner. Anticipatory compounding in limited quantities is allowed only for expected patient orders.
Primary Oversight
State board of pharmacy. FDA has residual authority. USP 795 and 797 sterility and quality standards apply.
Bulk Substances
Bulk drug substances used in 503A compounding must appear on the FDA's Section 503A Bulk Drug Substances List or a USP monograph, or be a component of an FDA-approved drug.
Prohibited
Large-scale manufacturing without individual prescriptions. Interstate distribution beyond a 5% limit unless the state signed a memorandum of understanding with FDA.
Section 503B
Outsourcing Facilities
A 503B outsourcing facility registers with the FDA and may compound in bulk without individual patient prescriptions. This pathway was created to legitimize higher-volume compounding for clinics, hospitals, and other health-care settings while enforcing manufacturing-grade quality standards.
Trigger for Compounding
May compound in advance of and without individual patient prescriptions, in larger batches, for shipment to health-care facilities.
Primary Oversight
FDA directly. Must comply with Current Good Manufacturing Practice (cGMP) standards, submit adverse event reports, and undergo FDA inspection.
Bulk Substances
Bulk drug substances must appear on the FDA's Section 503B Bulk Drug Substances List (a separate list from 503A). The list is narrower.
Registration
Facility must register annually with FDA as a Section 503B outsourcing facility and pay associated fees. Public FDA registry lists all facilities.
Peptides in Both Frameworks
Which Peptides Can Be Compounded?
The critical question for peptides is whether the specific compound appears on the applicable Bulk Drug Substances List. The FDA has published lists for both 503A and 503B contexts, and inclusion on one does not guarantee inclusion on the other. Several peptides commonly used in clinical practice — including semaglutide, tirzepatide, and BPC-157 — have been the subject of FDA guidance, warning letters, and inclusion or removal decisions that clinics should monitor.
FDA-Approved API Present?
If the peptide has a same-strength FDA-approved brand drug, compounding is typically not allowed unless documented shortage. Semaglutide (Ozempic, Wegovy) is the primary example.
On the 503A Bulk List?
If listed under 503A, a 503A pharmacy may compound patient-specific preparations. Not automatically permitted for 503B use.
Nominated Under 503A/503B?
Substances nominated but not yet listed exist in regulatory limbo. FDA enforcement discretion varies. Verify current status on the FDA website.
Not Approved for Compounding?
Peptides not on any list and without approved-drug status cannot be legally compounded for human use, regardless of research or clinical interest.
Verify before compounding: The FDA lists change. Consult the current published Section 503A Bulk Drug Substances List and Section 503B Bulk Drug Substances List before any compounding decision.
Research Supply Distinction
Where Research Peptides Fit
Research-grade peptides sold for laboratory use are governed by a different set of expectations. They are not compounded for or dispensed to individual patients, they carry "for research use only" labeling, and they are not intended to be administered to humans. This is why research suppliers can offer compounds that neither a 503A pharmacy nor a 503B facility could legally compound for clinical dispensing. It also means research peptides are not appropriate for clinical practice — the two supply chains serve different purposes under different regulatory expectations.
Have Compliance Questions?
This guide is educational, not legal advice. Practitioners considering compounded peptide protocols should consult licensed pharmacy counsel and verify the current FDA Bulk Drug Substances Lists directly.