FDA Category 2 peptides: the list, the reasons, and the 2026 changes

Where does Category 2 come from?

Pharmacies may compound from a bulk drug substance only if it qualifies under the statute (see 503A vs 503B). FDA builds the “bulks lists” of allowed substances by rulemaking, which is slow. In the meantime, it reviews nominations and sorts them into three interim categories:

Category	Meaning	Enforcement posture
1	Nomination had sufficient information; may be eligible	FDA generally does not intend to act against compounding while it evaluates
2	FDA has identified significant safety risks	No enforcement discretion
3	Nomination lacked sufficient information	No enforcement discretion

Polsinelli’s April 2026 analysis notes FDA placed 19 peptide or peptide-related substances in Category 2 during 2023.

Which peptides are still in Category 2?

From FDA’s table as checked on October 19, 2026:

Substance	503A / 503B	Date added	FDA’s stated concern (summary)
GHRP-2 (injectable and nasal)	503B	Sep 29, 2023	Immunogenicity, aggregation, impurities; unnatural amino acid; reported serious adverse events, causality not established
GHRP-6	503B	Sep 29, 2023	Immunogenicity; possible cortisol and blood-glucose effects
Ibutamoren mesylate	503A; 503B	503A Sep 29, 2023; 503B Dec 29, 2022	Possible congestive heart failure signal in a hip-fracture trial
Ipamorelin acetate	503B	Sep 29, 2023	Immunogenicity; unnatural amino acids; deaths reported with IV use in a gastric-motility study
Kisspeptin-10	503A	Sep 29, 2023	Immunogenicity, impurities; little safety data for proposed routes

(Ibutamoren is a small molecule, not a peptide, but it is usually discussed with growth-hormone secretagogue peptides.)

Which peptides were nominated but withdrawn?

FDA keeps a second table of substances “previously in category 2” whose nominations were withdrawn. Its safety language stays on the page. As of our check, the peptides listed there are:

Substance	FDA’s stated concern (summary)
AOD-9604	Immunogenicity, impurities; limited safety information; serious adverse events possibly associated
BPC-157	Immunogenicity, impurities, API characterization; little or no safety information for proposed routes
Cathelicidin LL-37	Immunogenicity; nonclinical findings on male reproduction and possible protumorigenic effects
CJC-1295	Immunogenicity; serious adverse events including increased heart rate and systemic vasodilatory reaction
Dihexa acetate	No human exposure data identified
Emideltide (DSIP)	Immunogenicity; no safety information for proposed route
Epitalon	Immunogenicity, aggregation; no safety information for proposed route
GHK-Cu (injectable routes)	Immunogenicity, aggregation; limited human data. Non-injectable GHK-Cu is back in Category 1 per FDA’s May 14, 2026 list (details)
Ipamorelin acetate	As above (also still Category 2 under 503B)
KPV	No human exposure data identified
PEG-MGF	No human exposure data identified
Melanotan II	Case reports of melanoma, PRES, sympathomimetic toxidrome, priapism
MOTS-c	No human exposure data identified
Selank acetate	Immunogenicity; lacks safety information
Semax	Immunogenicity; limited safety information
Thymosin alpha-1	Immunogenicity; inadequate safety information
TB-500 (thymosin beta-4 fragment)	Immunogenicity; no human exposure data identified

Why does FDA worry about peptides specifically?

FDA’s PCAC briefing on BPC-157 explains the reasoning behind most entries. Peptides, like therapeutic proteins, can provoke an immune response. That response can range from harmless antibodies to “life-threatening and catastrophic reactions.” Injected or nasal routes carry more immunogenic risk than oral ones. Peptides also tend to aggregate (clump into larger species), and aggregation is itself a risk factor for immunogenicity. Synthetic peptides carry peptide-related impurities, such as truncated or deleted sequences, that a simple purity number can miss. The testing side of this is covered in our HPLC and mass spectrometry explainers.

Does leaving Category 2 mean a peptide is allowed?

When nominations were withdrawn, FDA moved substances to the “withdrawn” table. In April 2026 it did this for 12 peptides and said it would still bring them to its advisory committee. Polsinelli wrote that this “does not, on its own, authorize use of that substance in compounding or bring it within FDA’s interim enforcement discretion policy for substances in Category 1.” The July 2026 advisory votes and the October interim policy at OMB are the next steps. Neither had changed the legal position as of October 19, 2026 (tracker).