503A vs 503B peptides: what each compounding pathway may do

503A and 503B are two sections of the US Federal Food, Drug, and Cosmetic Act that let compounded drugs skip FDA approval. A 503A pharmacy compounds against a patient-specific prescription and is exempt from manufacturing (CGMP) rules. A 503B outsourcing facility registers with FDA, must follow CGMP and may supply clinics without prescriptions. In neither case is a compounded peptide FDA approved. As of 2026-09-30, FDA has not added BPC-157 or any other peptide it reviewed in July 2026 to the 503A bulks list.

Item	Status
US FDA status	Compounded drugs are not FDA approved; FDA does not review them for safety, effectiveness or quality before sale (FDA)
Compounding: 503A	Kisspeptin-10 still in Category 2; 16 peptides withdrawn from Category 2 by nominators, none placed in Category 1 (FDA, 2026-04-22). PCAC voted on 7 peptides on 2026-07-23/24: 6 recommended, emideltide rejected; advisory, no FDA rule yet (FDA)
Compounding: 503B	GHRP-2, GHRP-6 and ipamorelin still in Category 2 (FDA). Exclusion of semaglutide, tirzepatide and liraglutide proposed 2026-04-30; no final decision found (FDA)
WADA 2026	Not changed by compounding status; e.g. BPC-157 is prohibited under S0 (USADA)
Strongest evidence	Not applicable: a legal framework, not a treatment
Human trials	Not applicable: compounded products reach patients without FDA premarket review
Next regulatory step	FDA notice-and-comment rulemaking for the PCAC peptides (none published); final 503B decision on the three GLP-1 drugs (pending)
Last checked	2026-09-30

503A vs 503B: how the two pathways differ

Compounding means a pharmacist or physician combining, mixing or altering ingredients to make a drug for a patient. Federal law exempts compounded drugs from several rules that apply to manufactured drugs only when they meet the conditions of section 503A or section 503B. The table sets out the conditions that matter most for peptides.

Feature	503A pharmacy	503B outsourcing facility
Who compounds	State-licensed pharmacist or physician (21 USC 353a)	A facility registered with FDA as an outsourcing facility (FDA)
Prescription	Required, for an identified patient (FDA)	Not required; may fill a provider’s order for office stock (FDA)
CGMP	Exempt (FDA)	Required, with risk-based FDA inspection (FDA)
Bulk ingredients	USP monograph, approved-drug component or 503A bulks list (FDA)	503B bulks list or FDA drug shortage list (FDA)
Copies of approved drugs	Not “regularly or in inordinate amounts” (21 USC 353a)	Not allowed unless on the shortage list (21 USC 353b)
Adverse-event reports to FDA	Not a 503A condition (21 USC 353a)	Required (FDA)
FDA-approved product	No (FDA)	No

A 503A pharmacy in a state that has not signed a memorandum of understanding with FDA may send no more than 5 percent of its compounded prescriptions out of state (21 USC 353a). An outsourcing facility must label each product “This is a compounded drug” or an equivalent statement, and no one other than the facility may sell or transfer the drug (21 USC 353b). Outsourcing facilities also send FDA lists of what they compounded every June and December (FDA).

Which peptides can a 503A pharmacy compound?

A 503A pharmacy may use a bulk drug substance, the raw active ingredient, only if it meets a USP or NF monograph, is a component of an FDA-approved drug, or appears on FDA’s 503A bulks list (FDA). The ingredient must also come from an FDA-registered manufacturer with a valid certificate of analysis (21 USC 353a). For a peptide with no monograph and no approved-drug use, the list is the only route, and the statute says that list is developed “through regulations”.

While that list is being built, FDA sorts nominated substances into interim categories. Under Category 1, FDA “does not intend to take action” against compounders. For Category 2, substances with identified safety risks, FDA “would consider taking action”. Category 3 covers nominations with too little supporting information. Substances nominated on or after 2025-01-07 are not placed in any category.

Peptides still in Category 2

Substance	Category 2 for	Listed since
GHRP-2	503B	2023-09-29
GHRP-6	503B	2023-09-29
Ipamorelin acetate	503B	2023-09-29
Kisspeptin-10	503A	2023-09-29
Ibutamoren (MK-677, non-peptide)	503A and 503B	503B 2022-12-29; 503A 2023-09-29

Source: FDA Category 2 page, content current as of 2026-04-22 (FDA).

Peptides withdrawn from Category 2

The same FDA page lists 16 substances as “previously in Category 2” and “withdrawn by nominators”: AOD-9604, BPC-157, cathelicidin LL-37, CJC-1295, dihexa acetate, emideltide (DSIP), epitalon, GHK-Cu (injectable routes), KPV, PEG-MGF, Melanotan II, MOTs-C, selank acetate, semax, thymosin alpha-1 and the thymosin beta-4 fragment TB-500. The page does not move any of them into Category 1. Some pages still describe these peptides as “Category 1” or “legal to compound”; the FDA page supports neither claim.

The July 2026 advisory committee votes

FDA’s Pharmacy Compounding Advisory Committee (PCAC) reviewed seven peptides for the 503A bulks list (FDA). On 2026-07-23 it considered BPC-157 for ulcerative colitis, KPV for wound healing and inflammatory conditions, TB-500 for wound healing and MOTs-C for obesity and osteoporosis. On 2026-07-24 it considered emideltide for opioid withdrawal, chronic insomnia and narcolepsy, Semax for cerebral ischemia, migraine and trigeminal neuralgia, and Epitalon for insomnia.

FDA has posted no minutes or vote summary. Trade press and a law-firm summary reported these counts: BPC-157, KPV and TB-500 each 8–6 with 1 abstention in favor; MOTs-C 7–5 with 2 abstentions; Semax 8–5; Epitalon 7–4; emideltide 6–7 against. The votes are advice to FDA. Adding a substance to the list requires regulations under section 503A (21 USC 353a), and FDA had published no proposed rule for these peptides when this page was checked.

Which peptides can a 503B outsourcing facility compound?

An outsourcing facility may compound from a bulk substance only if the substance is on the 503B bulks list, which covers substances for which FDA finds a “clinical need”, or if the finished drug is on FDA’s drug shortage list when it is compounded and distributed (FDA). The 503B interim categories use the same 1–2–3 structure as 503A. GHRP-2, GHRP-6 and ipamorelin are in Category 2 for 503B, so FDA would consider action against an outsourcing facility using them (FDA).

The shortage route explains the GLP-1 compounding boom. FDA declared the tirzepatide injection shortage resolved on 2024-12-19 and semaglutide on 2025-02-21 (FDA). Enforcement discretion for tirzepatide ended 2025-02-18 for 503A and 2025-03-19 for 503B. For semaglutide the stated end dates were 2025-04-22 (503A) and 2025-05-22 (503B), later extended by a court decision.

On 2026-04-30 FDA proposed excluding semaglutide, tirzepatide and liraglutide from the 503B bulks list, finding no clinical need. Commissioner Marty Makary said: “When FDA-approved drugs are available, outsourcing facilities cannot lawfully compound using bulk drug substances unless there is a clear clinical need” (FDA). The notice set a 2026-06-29 comment deadline. No final determination had been published by 2026-09-30.

Investigational peptides are a separate case. FDA states that “retatrutide and cagrilintide cannot be used in compounding under federal law” (FDA). Retatrutide is not obtainable legally outside clinical trials.

Why peptide length matters: the 40-amino-acid line

FDA defines a protein as “any alpha amino acid polymer with a specific, defined sequence that is greater than 40 amino acids in size” (21 CFR 600.3(h)(6)). Where several chains are naturally associated, their amino acids are counted together. A protein is regulated as a biological product, and FDA guidance states: “Biological products are not eligible for the exemptions in sections 503A and 503B of the FD&C Act” (FDA guidance). A chain of 40 amino acids or fewer is regulated as a drug and can, in principle, qualify under either section. A longer one cannot qualify under either, whatever list it is on. The peptides vs proteins explainer covers how the classes are defined.

What neither pathway covers: “research use only” products

Online sellers that label peptides “for research use only” are not operating under 503A or 503B. In an August 2026 warning letter, FDA wrote that “despite statements on your product labeling marketing your products for ‘research use only’ and ‘not for human consumption,’ evidence obtained from your website establishes that your products are intended to be drugs for human use”, and called them “unapproved new drugs” (FDA, 2026-08-24). The products named included retatrutide sold as “GLP-3R”, semaglutide, SS-31, PT-141 and tesamorelin. FDA’s GLP-1 page warns about products falsely marketed “for research purposes” or “not for human consumption” (FDA).

Safety: what the oversight difference means

Neither label, 503A or 503B, means FDA has checked a product. “Compounded drugs are not FDA approved. This means the agency does not review compounded drugs for safety, effectiveness or quality before they are marketed” (FDA). The two pathways differ in oversight after that point.

• Manufacturing standards: 503A pharmacies are exempt from CGMP; 503B facilities must comply with CGMP and are inspected by FDA on a risk-based schedule (FDA).
• Adverse-event reporting: outsourcing facilities must report adverse events to FDA (FDA).
• Reported harms, Human (spontaneous reports): as of 2026-05-31, FDA had received 990 adverse-event reports for compounded semaglutide and more than 730 for compounded tirzepatide, including dosing errors that led to hospitalization (FDA GLP-1 page, cited above). Such reports do not by themselves prove the drug caused the event.
• Different salt forms: for compounded GLP-1 products made with salts, FDA “does not have information on whether these salts have the same chemical and pharmacologic properties as the active ingredient in the approved drug”.
• Category 2 substances: FDA placed them there because it identified safety risks with their use in compounding (FDA).

Compliance with compounding rules says nothing about whether a peptide has been tested in people. The evidence for each peptide, and the gaps in it, is graded on that peptide’s own page, for example GHK-Cu.