Scientifically reviewed by Dr Stephan Hansberg
BPC-157 acetate vs free base vs arginate: salt forms (2026)
BPC-157 is sold as a free base, an acetate salt and an arginine salt (arginate). What differs chemically between them, what the FDA's July 2026 review said about free base and acetate, what the arginate patents claim, and how Celyfe documents the BPC-157 in the WOLVERINE Pen.
Key takeaways
- •All three forms share the same 15-amino-acid peptide; they differ in the counter-ion paired with it, which changes mass per mg, solubility, solution pH and stability.
- •Free base: CAS 137525-51-0, UNII 8ED8NXK95P, C62H98N16O22, 1419.5 g/mol. Acetate: CAS 216441-37-1, UNII PAR2FC72XP, with a variable acetate content.
- •The FDA's July 2026 review treated free base and acetate as two distinct bulk drug substances and found both not well characterised; it did not evaluate an arginate.
- •The arginine salt (Arg-BPC) comes from a 2013 Diagen patent claiming better heat and simulated gastric juice stability than the acetate or sodium salt; those are the applicant's own data, not independent peer-reviewed results.
- •The WOLVERINE Pen is labelled BPC-157 15mg with TB-500 15mg; its batch C26071 certificate (HPLC, 99%) is in the COA library at /coa.
The short answer
BPC-157 acetate, BPC-157 free base and BPC-157 arginate all contain the same peptide, Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val. The difference is the counter-ion: the free base has none, the acetate is paired with acetic acid, and the arginate is paired with the amino acid L-arginine. That changes the molecular weight of the material, how much peptide a milligram contains, and properties such as solubility and stability.
Regulators treat these as different substances. In its July 2026 review the FDA evaluated free base and acetate separately and found neither well characterised; the arginate was not part of that review.
Side by side
Free base and acetate identifiers are taken from the FDA's July 2026 briefing document; the arginate description is from the Diagen patent, as no regulator identifier for it was found.
| Property | Free base | Acetate | Arginate (Arg-BPC) |
|---|---|---|---|
| Counter-ion | None | Acetic acid (CH3COOH), variable number | L-arginine; described in the patent as a 1:2 salt |
| Formula | C62H98N16O22 | C62H98N16O22 . x(C2H4O2) | Peptide plus two L-arginine (patent description) |
| Molar mass | 1419.5 g/mol | Not fixed (depends on acetate content) | About 1768 g/mol by calculation for a 1:2 salt |
| CAS number | 137525-51-0 | 216441-37-1 | None found |
| FDA UNII | 8ED8NXK95P | PAR2FC72XP | None found |
| PubChem CID | 9941957 | 155977614 (record for a 1:1 acetate) | None found |
| FDA July 2026 review | Evaluated: not well characterised | Evaluated: not well characterised | Not evaluated |
| Main stability claim | FDA: expected stable below -18 C | FDA: expected stable below -20 C | Patent: improved heat and gastric juice stability vs acetate and sodium salt |
What differs chemically
The peptide chain is identical in all three. BPC-157 has acidic side chains (one glutamate, two aspartates and the C-terminal carboxyl) and basic groups (the N-terminal amine and a lysine), so it can pair with counter-ions in either direction. Solid-phase synthesis and reverse-phase HPLC purification normally leave a peptide as a salt of whatever acid was used in the final steps, which is why acetate salts are common for research peptides.
Mass per milligram. Counter-ions add weight. For an acetate the peptide fraction depends on how much acetate is present, which is why the FDA lists no fixed molecular weight for it. For a 1:2 arginine salt, two arginines (174.2 g/mol each) add about 348 g/mol to the 1419.5 g/mol peptide, so by simple arithmetic roughly 80% of the salt's mass is peptide. That is why a label should say whether a stated mg figure refers to the salt or to the peptide content.
Solution behaviour. The counter-ion sets the pH a peptide produces when dissolved, and pH affects solubility, aggregation and degradation. The FDA's briefing makes the general point directly: free bases, salts and esters of the same active moiety are distinct substances that may differ in solubility, permeability, melting point, stability and flow characteristics.
What the FDA's 2026 review considered
The FDA reviewed BPC-157 at the Pharmacy Compounding Advisory Committee on 23 July 2026, evaluating BPC-157 (free base) and BPC-157 acetate as two separate bulk drug substances. Both original nominations had been withdrawn, but the FDA chose to present them. It evaluated only one proposed use, ulcerative colitis.
On chemistry, the FDA found both forms not well characterised, for two reasons: inconsistent naming that does not follow established nomenclature (BPC-157 is a common name, not a USAN or INN, and the FDA said it had encountered multiple salts and derivatives sold under the same name), and missing data on critical quality attributes. Both nominations gave the free-base UNII and CAS number while attaching a certificate for the acetate, and the acetate certificates did not report specified impurities, aggregates, bioburden or endotoxins.
FDA staff proposed that neither form be added to the 503A bulks list, citing characterisation gaps, a lack of safety and immunogenicity information, insufficient evidence of effectiveness for ulcerative colitis and the availability of approved treatments. The committee nonetheless voted 8-6 with one abstention to recommend adding BPC-157. As of October 2026 the FDA had not completed rulemaking.
Where the arginate comes from
Salt forms of BPC-157 have been patented twice by groups linked to its original developers. A 1998 international application by Sikiric and colleagues (WO 1998/052973) described sodium, caesium, TRIS and other salts and reported them as more stable than BPC peptide acetates in saline or water. A 2013-priority application by Diagen d.o.o., inventor Rudolf Rucman (published as US 2016/0068572, granted as US 9,850,282), described salts with basic amino acids, including the L-arginine salt, as substantially more stable than previously known salts in heat testing and in simulated gastric juice at several pH values.
Two cautions apply. First, these are the applicants' own data in patent filings, not independent, peer-reviewed studies. Second, the FDA's 2026 review did not evaluate an arginate at all, so no regulator has assessed its characterisation. Some sellers also use the name pentadeca arginate; we could not find an official chemical identifier that defines that name, so we do not treat it as an established substance.
Regulatory status does not depend on the salt
Changing the counter-ion does not change how BPC-157 is regulated where it is named. WADA lists BPC-157 by name in S0 (non-approved substances), prohibited at all times, and Australia's Poisons Standard lists BPC157 in Schedule 4. In the UK there is no marketing authorisation for any form, and in the US no form is an approved drug.
How Celyfe documents BPC-157
The WOLVERINE Pen (/products/wolverine-pen) is labelled BPC-157 15mg and TB-500 15mg in a pre-filled, pre-mixed 3ml cartridge. Its batch certificate, batch C26071, was issued by Analiza Bialek in Wroclaw, Poland, reports 99% purity by HPLC and is dated 2 October 2026. It is published in the COA library at /coa, which is where to check exactly what was tested for the batch you receive.
BPC-157 15mg is also in the GLOW and KLOW pens, whose certificates are being re-issued and are listed in the COA library when published. Pens ship cold-chain and are kept refrigerated at 2 to 8 C; they should not be frozen.
Sources
Primary and official sources checked October 2026:
- FDA: Briefing document for BPC-157-related bulk drug substances (BPC-157 free base and BPC-157 acetate), Pharmacy Compounding Advisory Committee, 23-24 July 2026 (fda.gov)
- FDA: Briefing document introduction, Pharmacy Compounding Advisory Committee, 23-24 July 2026 (fda.gov)
- PubChem: BPC-157, CID 9941957; BPC 157 acetate, CID 155977614 (pubchem.ncbi.nlm.nih.gov)
- Sikiric P et al. New BPC peptide salts with organo-protective activity, the process for their preparation and their use in therapy. WO 1998/052973, published 26 November 1998
- Diagen d.o.o. (inventor Rucman R). New stable pentadecapeptide salts, a process for preparation thereof, a use thereof in the manufacture of pharmaceutical preparations and a use thereof in therapy. US 2016/0068572 A1, published 10 March 2016; granted as US 9,850,282 B2
- Jozwiak M et al. Multifunctionality and possible medical application of the BPC 157 peptide: literature and patent review. Pharmaceuticals, 2025. PMID 40005999
- AJMC: FDA panel backs 6 peptides for compounding, 31 July 2026
- Therapeutic Goods (Poisons Standard, October 2026) Instrument 2026, F2026L01327 (legislation.gov.au)
- WADA: Prohibited List 2026, S0, in force 1 January 2026 (wada-ama.org)
- Celyfe COA library: WOLVERINE batch C26071, Analiza Bialek, dated 2 October 2026 (/coa)
Research use only
Celyfe supplies research peptides for laboratory and research use only. Nothing on this page is guidance on use in humans or animals.
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