TB-500 Peptide: What It Is and Where the Name Came From

TB-500 is a common name for a synthetic peptide of seven amino acids, N-acetyl-Leu-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ), that matches residues 17 to 23 of the protein thymosin beta-4. A supplier listing for the 5 mg material is Curo's TB-500 5mg listing.

What is TB-500?

Thymosin beta-4 is a protein of 43 amino acids. TB-500 copies seven of them and adds an acetyl group at the start of the chain. FDA's Substance Registration System keeps a separate record for each: UNII QHK6Z47GTG for TB-500 and UNII 549LM7U24W for thymosin beta-4. Sources: FDA UNII record for TB-500 and FDA UNII record for thymosin beta-4.

FDA's 2026 briefing document on TB-500 comments on the name. It states that "TB-500 is a common name and not a United States Adopted Name (USAN)" and that FDA "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.

The Research Peptide Guide TB-500 page covers the difference between the fragment and the full protein in more detail.

Which identifiers belong to TB-500?

• PubChem compound record CID 62707662. PubChem lists the compound under the title Unii-qhk6Z47gtg, with TB-500, TB500 and TB 500 among its synonyms.

• Molecular formula C38H68N10O14 and molecular weight 889.0 g/mol, both from the PubChem record.

• CAS Registry Number 885340-08-9, which the PubChem and FDA records both list as a synonym.

• FDA UNII QHK6Z47GTG, preferred substance name TB-500.

Sources: PubChem record for TB-500, CID 62707662 and FDA UNII record for TB-500. The FDA record carries this note: "UNII availability does not imply any regulatory review or approval."

Open the TB-500 source ledger.

Where did the name TB-500 come from?

The earliest sources cited here use the name TB-500 for a veterinary product. FDA's briefing document dates a veterinary preparation of TB-500 to 2011 and says it was marketed to boost performance in equine and greyhound sports. Source: FDA briefing document for TB-500, May 15, 2026.

Two 2012 papers addressed doping control. One developed a method to detect N-acetylated LKKTETQ and its breakdown products in horse urine and plasma, and described it, to the authors' knowledge, as the first identification of TB-500 and its metabolites in samples from horses that had received the product. Source: 2012 horse doping-control paper, PMID 23084823. The other identified Ac-LKKTETQ in a TB-500 formulation that the authors described as suspected to be used as a doping agent in sport. Source: 2012 TB-500 identification paper, PMID 22962027.

WADA's research page for a 2013 TB-500 project says the product was presented as "the synthetic peptide of the active region of thymosin-beta 4 (Tβ4)", "without any further qualitative description such as amino acid sequence or molecular weight." The investigators reported that they had identified the active content as Ac-LKKTETQ. Source: WADA research project page for TB-500 metabolism, project 13D34PV.

These papers describe how to detect and identify a veterinary product. They did not test what the product does.

Is TB-500 approved, and is it allowed in sport?

FDA's briefing document says there is no applicable United States Pharmacopeia or National Formulary monograph for TB-500 (free base) or its acetate form, "and neither is a component of an FDA-approved drug." Source: FDA briefing document. WADA's 2026 Prohibited List names "Thymosin-ß4 and its derivatives e.g. TB-500" in section S2.3. Source: WADA 2026 Prohibited List. The TB-500 side effects page sets out the FDA and WADA records with their dates.

Where do the benefit claims and the material listings fit?

Claims about what TB-500 does are listed with the studies behind them on the TB-500 benefits page. Listings that use the name are compared with the FDA and PubChem records on the TB-500 for sale page. For the supplier's certificates, open Curo's lot certificates.