Evidence-graded review / Research peptide — Ac-LKKTETQ
TB-500 is the Ac-LKKTETQ heptapeptide of thymosin beta-4 — here is what the published research actually verifies.
A record of the structural biochemistry, the preclinical findings, and the regulatory boundaries, with every quantitative claim stamped by its evidence status and backed by a linked citation.
The TB-500 record, graded
TB-500 is a synthetic, N-terminally acetylated heptapeptide with the sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ). It corresponds to residues 17-23 of thymosin beta-4, the body's principal G-actin-sequestering peptide, and that segment is the conserved actin-binding motif of the beta-thymosins [1]. This review grades the TB-500 record: what the peer-reviewed literature verifies, what is preclinical only, and where no human data exist.
One fact sits above the rest, so it is stated first. There is no completed controlled clinical trial of the TB-500 heptapeptide for any indication [6]. The human safety data that exist are for full-length thymosin beta-4, not the seven-amino-acid fragment [6]. Most of the efficacy literature attributed to "TB-500" was generated with the full-length ~4963 Da parent protein, not the ~889 Da fragment marketed under that name [5][7]. We flag that identity distinction wherever a finding rests on the full-length protein, because it is the single most consequential caveat in the record.
What is verified is structural. X-ray crystallography resolved the way the molecule works: full-length thymosin beta-4 forms a 1:1 complex with monomeric (G-) actin and sequesters it by capping both ends of the monomer, the mechanism that underlies the whole beta-thymosin family [1]. From there the literature is a graded mix — reproducible preclinical findings in wound, cardiac, neurological and hair-follicle models, an honest set of null and counter-results, and a regulatory picture that is fixed and citable: not an FDA-approved drug, placed by FDA in 503A Category 2, and prohibited by the World Anti-Doping Agency in sport.
What Is the TB-500 Peptide?
The TB-500 peptide is the synthetic Ac-LKKTETQ fragment of thymosin beta-4 — seven amino acids carrying the actin-binding active site of a 43-residue parent protein [5]. Its molecular weight is 889.02 Da and its formula is C38H68N10O14. In commerce and in the analytical anti-doping literature, the name "TB-500" denotes this heptapeptide specifically, supplied as a veterinary preparation with an artificially acetylated N-terminus [7].
The distinction matters because the parent protein is much larger. Thymosin beta-4 (gene TMSB4X, ~4963 Da) is present in nearly all human cells and is released by platelets and macrophages at sites of injury [5]. The LKKTETQ region in TB-500 is its actin-binding core, but the isolated seven-mer is a synthetic construct, not an endogenous species [5]. Whether the fragment reproduces the full protein's effects at the doses used in peptide research is not established in any controlled human trial [6].
This site treats the "reviews" question as a fiduciary one. Rather than star ratings or anecdote, it grades each claim against the published record and links the proof. The deep dive lives across TB-500 mechanism of action, thymosin beta-4 and TB-500, and TB-500 detection and WADA status.
What Is TB-500?
TB-500 is a synthetic, N-terminally acetylated heptapeptide (Ac-LKKTETQ) corresponding to residues 17-23 of thymosin beta-4, the body's principal G-actin-sequestering peptide [5]. The LKKTETQ motif is the actin-binding region of the beta-thymosins [1]. In commerce and anti-doping science the name denotes this seven-mer specifically — not the full-length parent protein [7].
What Does TB-500 Stand For?
TB refers to thymosin beta. The "TB-500" designation is a research and commercial name for the synthetic Ac-LKKTETQ fragment of thymosin beta-4; in commerce and in anti-doping science the name denotes the heptapeptide [7]. It is not an official drug name, an INN, or an FDA-recognized identifier. The 500 is a product-series label, not a dose, a potency, or a molecular figure — the actual molecular weight of the fragment is 889.02 Da [5].
The evidence boundaries, in one view
Three boundaries frame everything on this site, and each is read first rather than buried. The fragment has no completed controlled human trial, so its human safety and efficacy profile is uncharacterized [6]. The efficacy literature is dominated by full-length thymosin beta-4, so a "TB-500 benefit" is usually a thymosin beta-4 finding wearing the fragment's name [5][7]. And the regulatory status is fixed and citable: TB-500 is not FDA-approved, FDA placed "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" in 503A Category 2 effective with its September 29, 2023 update, and the World Anti-Doping Agency prohibits it in sport [15].
From here, three routes through the record. The mechanism and the preclinical findings are on TB-500 and BPC-157 research and the rest of the research page. The dose quantities studied in named species, the half-life question, and the routes are on TB-500 dosing quantities in the literature. The detection science the equine-doping context produced is on the detection page, and the full source list is at TB-500 references and citations.