FDA 503A Bulk Drug Lists and Research Peptides

Section 503A of the Federal Food, Drug, and Cosmetic Act (FD&C Act) governs which bulk drug substances state-licensed pharmacies and physicians may use when compounding a drug for a specific patient. FDA sorts substances nominated for the 503A bulks list into three interim categories, Category 1, 2 and 3, based on how much safety information is available. Several peptides discussed in the research community, including BPC-157, kisspeptin-10 and others, have appeared on FDA's Category 2 list at one point or another, a compounding-pharmacy classification that is separate from how peptides sold for laboratory research are labeled and regulated.

What is Section 503A of the FD&C Act?

Section 503A describes conditions under which compounded drugs are exempt from certain FD&C Act requirements, including the requirement that a drug have FDA approval before it is marketed. FDA states that state-licensed physicians and pharmacists compounding under Section 503A may use a bulk drug substance only if it complies with an applicable United States Pharmacopeia (USP) or National Formulary (NF) monograph, is a component of an FDA-approved drug product, or appears on FDA's 503A bulks list (FDA, Bulk Drug Substances Used in Compounding Under Section 503A). The substance must also come with a valid certificate of analysis from a facility registered with FDA under section 510 of the FD&C Act.

This framework applies to compounding pharmacies and physicians preparing patient-specific prescriptions. It does not describe or govern how a chemical supplier labels, sells, or ships material intended for laboratory research rather than for compounding into a drug for a patient.

What are FDA's three bulk drug substance categories?

FDA developed an interim policy describing three categories of nominated bulk drug substances while it evaluates them for the 503A bulks list. The table below uses FDA's own language for each category (FDA, Bulk Drug Substances Used in Compounding Under Section 503A).

Category	FDA's definition	What it means for compounding
Category 1	Nominated with sufficient supporting information for FDA to evaluate, and does not appear on any other list.	FDA does not intend to take action against a compounder using the substance, provided the conditions in FDA's guidance are met.
Category 2	Nominated with sufficient supporting information, but FDA has identified significant safety risks relating to use of the substance in compounding.	FDA does not extend the Category 1 enforcement policy to these substances and states it would consider taking action against a compounder using them.
Category 3	Nominated with insufficient supporting information for FDA to evaluate.	Not eligible for the Category 1 policy; substances can be re-nominated with more supporting data.

FDA has also stated that it does not intend to place bulk drug substances nominated on or after January 7, 2025 into these three categories going forward, under a revised interim policy (FDA, Interim Policy on Compounding Using Bulk Drug Substances Under Section 503A of the FD&C Act).

Which peptides has FDA placed in Category 2?

FDA publishes the substances it has placed in Category 2, along with a summary of the safety concern for each and the date it was added, on a page titled Certain Bulk Drug Substances for Use in Compounding That May Present Significant Safety Risks. The list is shared between Section 503A (pharmacies and physicians) and Section 503B (outsourcing facilities), and each entry states which section it applies to.

Peptides and related substances currently in Category 2

As FDA's page currently lists them: kisspeptin-10 (Category 2 under Section 503A, added September 29, 2023) and ibutamoren mesylate (Category 2 under both Section 503A and Section 503B). Growth hormone releasing peptide-2 (GHRP-2), growth hormone releasing peptide-6 (GHRP-6), and ipamorelin acetate are also listed in Category 2, but FDA's table marks them as Section 503B only, meaning they are not currently a 503A Category 2 entry (FDA, Certain Bulk Drug Substances for Use in Compounding That May Present Significant Safety Risks). Our overview of growth hormone secretagogues in research, including ipamorelin, covers the published literature on this peptide class in more detail.

Peptides nominated into Category 2 and later withdrawn

FDA's page also lists a separate group of bulk drug substances that were previously in Category 2 but were withdrawn from that status by the parties who nominated them, including BPC-157, AOD-9604, CJC-1295, thymosin beta-4 fragment (TB-500), thymosin-alpha 1, melanotan II, epitalon, GHK-Cu, KPV, MOTS-C, selank acetate, semax, dihexa acetate, and emideltide (also known as DSIP) (FDA, Certain Bulk Drug Substances for Use in Compounding That May Present Significant Safety Risks). A withdrawn nomination is not the same as a Category 1 finding of no significant safety concern; it means the nomination that placed the substance in Category 2 is no longer active, and FDA is not currently applying its Category 2 enforcement position to that substance on this list.

Our lot pages for BPC-157 and AOD-9604 describe how each research-grade material is supplied and tested; neither page describes a route of administration or dose for a person or animal, because that is outside what Section 503A, or FDA's Research Use Only framework, covers for a laboratory product.

Peptides under active advisory committee review

Separately from the Category 2 list, FDA's Pharmacy Compounding Advisory Committee (PCAC) met on July 23 to 24, 2026 to discuss whether several bulk drug substances should be added to the 503A bulks list itself. According to FDA's meeting page, the committee discussed BPC-157, KPV, TB-500, and MOTS-C on July 23, and emideltide (DSIP), semax, and epitalon on July 24, each tied to a specific use FDA had reviewed for that substance (FDA, July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee). Advisory committees give FDA non-binding recommendations; the agency is not required to follow them, and inclusion on the 503A bulks list is a separate, later regulatory step from a committee discussion.

What does a Category 2 listing mean, and what does it not mean?

A Category 2 listing is a statement by FDA that it has identified a significant safety concern with using a specific bulk substance to compound a drug for a patient, and that FDA would consider enforcement action against a compounder who uses it. It does not mean the substance has been scheduled as a controlled substance; drug scheduling is a separate action under the Controlled Substances Act and is not part of the 503A bulks list process. It also does not create or change any standard for material that is manufactured, labeled, and sold for laboratory research rather than for compounding into a human or animal drug. Section 503A, by its own terms, addresses what state-licensed pharmacies and physicians may use when compounding a patient-specific prescription; it does not address in vitro research conducted with a labeled research chemical.

How does Research Use Only labeling fit in?

Research Use Only (RUO) labeling states that a product is supplied for laboratory research and is not intended for human or animal use. It is a labeling and intended-use framework, distinct from the 503A bulks list categories described above. Our article on what Research Use Only means explains why the label appears on every vial and what it signals to a laboratory customer.

What have FDA's warning letters to peptide sellers focused on?

FDA has issued warning letters to a number of online peptide sellers. In letters FDA has published, the agency's stated basis is not the RUO label itself but evidence, drawn from a seller's website, that the products are intended for human use, for example, disease-treatment or therapeutic-effect claims made about a product, or bacteriostatic water sold alongside peptides in a way that FDA reads as providing the means to prepare an injectable product for a person. FDA has concluded in these letters that such products are unapproved new drugs under section 505(a) of the FD&C Act, 21 U.S.C. 355(a), and that introducing them into interstate commerce under those conditions violates the FD&C Act, regardless of the RUO label on the product (FDA, Warning Letter to Peptide Partners LLC; FDA, Warning Letter to Wholesale Peptide).

What does a compliant research vendor do?

Based on what FDA's warning letters describe as the basis for enforcement, a vendor selling peptides for laboratory research keeps its labeling, marketing, and product pages limited to research use: no claims about treating, curing, or improving a condition in a person or animal, no dosing or administration instructions written for a person, and no bundling of reconstitution solvent with a peptide in a way that implies preparation for injection into a person. A certificate of analysis (COA) for each lot, covering identity and purity testing, supports the research-use claim with data rather than marketing language. Our guide to how to read a peptide certificate of analysis walks through what a COA should show and how to check it against the lot on hand.

Frequently asked questions

Is a peptide in FDA's Category 2 illegal to sell?

Category 2 is a compounding-pharmacy classification under Section 503A and Section 503B. It states FDA's position on using a bulk substance to compound a drug for a patient. It is not, by itself, a statement about a research chemical sold with Research Use Only labeling and no human-use claims; those products are evaluated under different provisions of the FD&C Act, as FDA's warning letters illustrate.

Does Category 2 mean the substance is scheduled by the DEA?

No. Drug scheduling under the Controlled Substances Act is a separate legal process from FDA's 503A bulks list categories. A Category 2 listing addresses compounding safety information under the FD&C Act; it is not a scheduling action.

Why was BPC-157 removed from FDA's Category 2 list?

FDA's Category 2 page lists BPC-157 in a separate table of substances that were withdrawn by the parties who nominated them for Category 2. FDA's page does not state a reason for each withdrawal. Separately, FDA's Pharmacy Compounding Advisory Committee has since discussed BPC-157 as a candidate for the 503A bulks list itself, a different and ongoing process.

Does the 503A bulks list apply to research suppliers?

Section 503A applies to state-licensed pharmacies and physicians compounding drugs for specific patients. It does not describe requirements for a supplier that manufactures and labels a peptide as Research Use Only for laboratory use.

What should I check before treating a peptide as "research use only" in practice?

Look for a certificate of analysis specific to the lot, confirmation that the product page makes no claims about effects in a person or animal, and labeling that states the product is not for human or animal use. Our guide on spotting a bad peptide vendor lists other red flags to check.

Where can I read FDA's own list instead of a summary?

FDA's Category 2 page and its main Section 503A bulk drug substances page, both linked in the references below, are the primary sources and are updated by FDA directly.

References

Research use only. Homegrown Peptides products are for laboratory research and are not for human or animal use. Nothing in this article is medical advice.