TB-500 vs Thymosin Beta-4: What TB-500 Actually Is
TB-500 is often described as thymosin beta-4. The literature, and a one-line mass calculation, show it is a seven-amino-acid fragment.
Listings often use TB-500 and thymosin beta-4 as if they were the same thing. They are not. Thymosin beta-4 (Tb4) is a 43-amino-acid protein that is the major actin-sequestering molecule in eukaryotic cells. TB-500, as the doping-control and orthopaedic literature describes it, is a short synthetic fragment of it. The difference matters for what a vial contains, for what the research literature can be applied to, and for how to read a certificate.
What the literature says TB-500 is
In 2012 a Hong Kong racing laboratory described TB-500 as a veterinary preparation containing a synthetic version of the peptide LKKTETQ, the segment at residues 17 to 23 of thymosin beta-4 that is the active site for actin binding, cell migration and wound healing, with artificial acetylation of the N-terminus. The same year a Ghent doping-control laboratory identified the N-terminal acetylated 17-23 fragment, Ac-LKKTETQ, in TB-500 by high-resolution mass spectrometry and synthesised it for reference.
A 2026 review in the Journal of the American Academy of Orthopaedic Surgeons says the same: TB-500 is a distinct seven-amino-acid fragment of Tb4 that is frequently conflated with the full-length protein, despite the absence of validated biological or clinical equivalence.
A calculation you can repeat
The certificate for our TB-500 batch TB-2608 gives the formula C38H68N10O14 and a molecular weight of 889.02. You can check that this is the acetylated fragment. The residues of Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln weigh about 113.16 for leucine, 128.17 for each of two lysines, 101.10 for each of two threonines, 129.12 for glutamate and 128.13 for glutamine, which sum to about 829.0. Adding one water for the peptide termini gives about 847.0, and the N-terminal acetyl group adds about 42.0, for 889.0 in total.
Full-length thymosin beta-4 weighs roughly 5,000. A certificate that gives a molecular weight near 889 is therefore describing the heptapeptide fragment, and one that gives a figure near 5,000 would be describing the whole protein. Checking the mass on the certificate is the quickest way to tell which one a listing means.
What has been studied: fragment and full-length are different bodies of work
Most of the human experience with thymosin beta-4 involves the full-length protein. In a randomised, placebo-controlled, double-masked Phase III trial of 0.1% RGN-259 ophthalmic solution in neurotrophic keratopathy, complete healing at four weeks occurred in 6 of 10 treated subjects and 1 of 8 on placebo (p = 0.0656), which the authors called a strong efficacy trend. Several authors are affiliated with the companies behind the product, and this was an eye-drop trial of the full-length protein, so it says nothing about the fragment or about injection.
For the fragment, the evidence is cellular and animal. A 2010 review by Sosne and colleagues describes a short sequence containing LKKTETQ, the central actin-binding domain at residues 17 to 23 plus one more amino acid, as promoting angiogenesis, wound healing and cell migration, while other regions of the protein carry different activities, such as the Ac-SDKP region that generally blocks inflammation. In the 2026 rat Achilles tendon study, the TB-500 group had significantly higher maximum load to failure and lower tendon degeneration scores than controls, and combining it with BPC-157 added nothing. The orthopaedic review adds that direct musculoskeletal evidence for Tb4 is limited to in vitro and rodent work, and that the compounds remain banned in sport.
How to read this
Treat TB-500 and Tb4 as two different research compounds. Claims drawn from full-length Tb4 work, such as the ophthalmic trials, should not be assumed to apply to the fragment, and vice versa. Always ask what the certificate says the molecular weight and formula are.
QSC supplies TB-500 in 5 mg, 10 mg and 20 mg vials strictly for laboratory research. It is not approved for human or veterinary use, and nothing here is a dosing recommendation. See also our BPC-157 research evidence article.
Sources
Ho EN et al. Doping control analysis of TB-500, a synthetic version of an active region of thymosin beta-4, in equine urine and plasma by liquid chromatography-mass spectrometry. Journal of Chromatography A, 2012;1265:57-69. doi:10.1016/j.chroma.2012.09.043. PMID 23084823.
Esposito S et al. Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential. Drug Testing and Analysis, 2012;4(9):733-738. doi:10.1002/dta.1402. PMID 22962027.
Sosne G, Qiu P, Goldstein AL, Wheater M. Biological activities of thymosin beta4 defined by active sites in short peptide sequences. FASEB Journal, 2010;24(7):2144-2151. doi:10.1096/fj.09-142307. PMID 20179146.
Sosne G et al. 0.1% RGN-259 (thymosin beta-4) ophthalmic solution promotes healing and improves comfort in neurotrophic keratopathy patients in a randomized, placebo-controlled, double-masked Phase III clinical trial. International Journal of Molecular Sciences, 2022;24(1):554. doi:10.3390/ijms24010554. PMID 36613994.
Tham A et al. Investigational peptides in orthopaedic practice: evidence, safety, and patient counseling for BPC-157, thymosin beta-4 and TB-500. Journal of the American Academy of Orthopaedic Surgeons, 2026 (online ahead of print, 27 October 2026). doi:10.5435/JAAOS-D-26-00049. PMID 42937313.
Bicer O et al. Effects of BPC-157 and TB-500 on Achilles tendon healing in rats. Joint Diseases and Related Surgery, 2026;37(3):822-837. doi:10.52312/jdrs.2026.2951. PMID 42542926.
