Research material and lot documents
TB-500 for sale listings can describe different substances under one name. FDA's 2026 briefing says it "has encountered multiple salts, and derivatives, including different active moieties, sold commercially under the same common name." Source: FDA briefing document for TB-500, May 15, 2026. A supplier listing for the 5 mg material is Curo's TB-500 5mg listing.
FDA's briefing treats TB-500 (free base) and TB-500 acetate as two different bulk drug substances. It states: "All distinct active moieties, as well as free bases, salts, or esters of any given active moiety, are distinct BDSs for these reasons." Its comparison table gives these records:
UNII: QHK6Z47GTG.
CAS number: 885340-08-9.
Molecular formula and weight: C38H68N10O14, 889.01 g/mol.
UNII: not available.
CAS number: not available.
Molecular formula and weight: C38H68N10O14·CH3COOH, 949.1 g/mol.
Source: Table 1 of the FDA briefing document. A footnote to that table states: "On several suppliers' websites, the CAS number for TB-500 (free base) (885340-08-9) is used for TB-500 Acetate."
Full-length thymosin beta-4 is a third substance, with UNII 549LM7U24W and 43 amino acids. Source: FDA UNII record for thymosin beta-4. The TB-500 peptide guide gives the sequence and mass of TB-500 for comparison with a listing.
FDA reviewed a representative public certificate for TB-500 (free base). Per the briefing, it included only appearance, identity by liquid chromatography-mass spectrometry and HPLC, and peptide purity. FDA states: "However, assay, impurities, bacterial endotoxins, and aggregates are not tested or controlled for TB-500 (free base)." For the TB-500 acetate certificate in the withdrawn nomination, FDA reports: "Testing results are not provided for Identification, Assay, Aggregates, and Bacterial Endotoxin levels." Source: FDA briefing document.
One supplier's testing page defines the fields on its reports. Identity is by FTIR or LC-MS, purity is the target compound as a percentage of total detected peak area, and fill is the measured amount of material in each vial. Endotoxin and sterility are listed where available. Source: Curo's testing page. A reader can set the fields on any lot report beside FDA's list, and check that the report names the form, free base or acetate, and that its lot number matches the vial.
The 5 mg in a listing name is the stated material amount per vial. A fill result on a lot report is a separate measurement of the material in the vial, and a purity percentage reports the target compound as a share of the detected peak area. FDA's description of the public certificate lists purity and assay as separate tests. Sources: the supplier testing page above and the FDA briefing document.
The supplier's lot reports are in Curo's COA library, and the supplier's category page for recovery research material is Curo's recovery and regenerative research category. A report for one lot supports statements about that lot. A supplier's page is a statement by the supplier.
FDA's briefing says neither form of TB-500 is a component of an FDA-approved drug. FDA's UNII record carries the note "UNII availability does not imply any regulatory review or approval." Sources: FDA briefing document and FDA UNII record for TB-500.
FDA's records list them under separate UNIIs, TB-500 with 7 amino acids and thymosin beta-4 with 43. The briefing states: "thymosin beta-4 and TB-500 are not the same substance." Sources: FDA UNII record for TB-500, FDA UNII record for thymosin beta-4 and FDA briefing document.