TB-500 research: what the evidence actually shows

Research-use notice: this article is for legitimate laboratory and educational research only. It does not provide guidance for human use, administration, dosing or treatment.

TB-500 is a trade name, not a molecule with its own research literature. It refers to a synthetic peptide modelled on a seven-residue segment of thymosin beta-4 (Tβ4), a 43-amino-acid protein found in almost every human cell. Nearly everything written about TB-500 in wound, tendon and cardiac models was actually done with full-length Tβ4, in animals, by a small number of laboratories. The peer-reviewed record on the seven-residue fragment itself amounts to two 2003 papers from the laboratory that first reported Tβ4’s wound effects, and a handful of doping-control chemistry papers that describe how to detect it in horses. There are no human trials of TB-500, it is not a licensed medicine anywhere, and it is named on the World Anti-Doping Agency Prohibited List. This article sets out what the Tβ4 research does and does not show, and why the two should not be confused.

What is TB-500?

TB-500 is the name under which a short synthetic peptide has been sold since at least the late 2000s, first encountered in horse racing and later on the research-chemical market. Its sequence is residues 17 to 23 of thymosin beta-4 (Leu-Lys-Lys-Thr-Glu-Thr-Gln, or LKKTETQ) with an acetyl group on the N-terminus. That segment contains the hexapeptide motif (LKKTET) through which Tβ4 binds actin, which is why the fragment is sometimes called the “active region” of Tβ4.

One practical complication: the name is used loosely. Some vendors sell the seven-residue acetylated fragment as TB-500; others sell full-length synthetic Tβ4 under the same name, or label a vial “TB-500 / Thymosin Beta-4” without saying which it contains. These are different molecules with more than a five-fold difference in mass, indistinguishable as a white powder. The batch laboratory report should state the sequence and an observed mass; if it does not, the identity of the material is unknown. Our guide What are peptides? covers the basics of sequences and synthesis.

Thymosin beta-4: the protein TB-500 is cut from

Thymosin beta-4 was first isolated from calf thymus in the early 1980s and named as a thymic hormone before its real job became clear. It is the main actin-sequestering protein in mammalian cells, binding monomeric (G-) actin and keeping it from polymerising into filaments. Cells draw on that reservoir to rebuild their cytoskeleton when they move, which is why Tβ4 turns up in studies of cell migration, wound repair and development.

The 1996 mutational study by Van Troys and colleagues in The EMBO Journal is the reason TB-500 exists. Testing altered versions of Tβ4 against actin, the group mapped the binding to two regions: the N-terminal residues 1 to 16, which must fold into an alpha-helix, and the hexapeptide motif at residues 17 to 22. The fragment copies the second region and leaves out the first, and Van Troys found that both contribute to actin binding.

What the thymosin beta-4 research shows

The claims attached to TB-500 come almost entirely from Tβ4 papers. Those papers are real, so it is worth being precise about what they contain.

Animal and cell models

• Skin wounds (rats). Malinda and colleagues at the US National Institutes of Health reported in 1999 that topical or injected Tβ4 increased re-epithelialisation of full-thickness punch wounds in rats by 42% at four days and up to 61% at seven days compared with saline, with increased collagen deposition and angiogenesis. This is the founding wound paper, and it used the 43-residue protein.
• Cornea (mice). Sosne and colleagues reported in 2002 that topical Tβ4 accelerated re-epithelialisation of alkali-burned mouse corneas and reduced neutrophil infiltration and inflammatory cytokine expression. This is the preclinical basis of the RGN-259 eye-drop programme.
• Heart (mice). Two Nature papers carry most of the weight here. Bock-Marquette and colleagues (2004) found that Tβ4 forms a complex with PINCH and integrin-linked kinase, activates the survival kinase Akt, and improved cardiomyocyte survival and heart function after coronary ligation in mice. Smart and colleagues (2011) reported that Tβ4 priming activated epicardium-derived progenitor cells in adult mice, which went on to form new cardiomyocytes after injury.

Goldstein, Hannappel and Kleinman summarised this work in a 2005 Trends in Molecular Medicine review. The common thread is that Tβ4 acts through several mechanisms at once: actin sequestration, the ILK–Akt survival pathway, reduced inflammatory signalling and new blood vessel formation. All were demonstrated with the full protein, largely by laboratories associated with Tβ4’s discoverers or with RegeneRx, the company that licensed it.

Human trials of thymosin beta-4

Tβ4, unlike TB-500, has been given to people in controlled trials. The results are more modest than the animal work.

Two things follow. Tβ4 is one of the better-studied peptides in this category in humans, with phase 1 safety data and over a thousand trial participants. Yet after roughly fifteen years of clinical development its primary endpoints have repeatedly been missed, and it is not an approved medicine for any indication. The fairest summary of the Tβ4 clinical record is “tolerated at the doses tested, efficacy unproven”.

Why thymosin beta-4 results do not transfer to a seven-residue fragment

It is tempting to treat TB-500 as a convenient short version of Tβ4. The structural biology argues against that.

• The fragment lacks half the actin-binding site. Van Troys showed that Tβ4 holds actin with both its N-terminal helix (residues 1–16) and the LKKTET motif. TB-500 carries only the motif, so on the published mapping it should not sequester actin the way the parent protein does. That weakens the mechanism most Tβ4 papers are built on.
• The cardiac mechanism was mapped on the full protein. The PINCH–ILK–Akt complex in Bock-Marquette’s work and the epicardial activation in Smart’s were observed with 43-residue Tβ4. No published study has shown the 17–23 fragment does either.
• Size changes behaviour in a living system. A 4,963 Da protein and an 889 Da peptide differ in clearance, degradation, tissue distribution and cell uptake. Ho and colleagues found TB-500 metabolites in horse plasma and urine, showing the fragment is metabolised in vivo; nothing is published on its behaviour in humans.
• Different laboratories, different questions. The Tβ4 literature asks what the protein does; most of the TB-500 literature asks how to catch it in a doping test. Apart from two 2003 papers from the Kleinman group (below), nobody has published the Malinda, Sosne or Bock-Marquette models run with the heptapeptide, and nobody has published them with the acetylated form sold as TB-500.

Whether a fragment retains any activity of its parent is an empirical question for independent, controlled experiments. For TB-500, those experiments have barely begun. A result in a Tβ4 paper is a result about Tβ4.

What has actually been published on the fragment

The peer-reviewed record on the 17–23 fragment is short. It begins with two papers from the US National Institutes of Health group that produced the original Tβ4 wound work, then falls silent on biology and becomes forensic.

• Philp et al., The FASEB Journal, 2003. Kleinman’s group reported that a synthetic seven-residue peptide covering the actin-binding motif had angiogenic activity in their endothelial-cell assays comparable to full-length Tβ4 at about 50 nM, while shorter or altered versions were inactive. The published abstract does not state whether the peptide was N-acetylated.
• Philp et al., Wound Repair and Regeneration, 2003. The same group reported that full-length Tβ4 accelerated full-thickness wound repair in diabetic (db/db) and aged mice, and that the seven-residue peptide LKKTETQ promoted repair in the aged mice to a degree comparable with the parent protein. Again, the abstract does not specify acetylation. These two papers are the only published biology of the fragment, they come from a laboratory whose members hold patents on Tβ4 wound treatment, and they have not been independently replicated or extended in the two decades since.
• Ho et al., Journal of Chromatography A, 2012. The Hong Kong Jockey Club racing laboratory developed an LC–MS method for TB-500 and its metabolites in equine urine and plasma, with detection limits of 0.01 and 0.02 ng/mL, and confirmed the peptide and its metabolites in samples from treated horses. The paper describes the compound as N-acetylated LKKTETQ.
• Esposito et al., Drug Testing and Analysis, 2012. The Ghent doping-control laboratory identified the active component of a commercial TB-500 product by high-resolution mass spectrometry, then synthesised the acetylated 17–23 fragment to confirm the structure. The title describes TB-500 as “a product suspected to possess doping potential”; the paper reports no biological experiments.
• Davison and Brown, Journal of Sports Sciences, 2013. A two-page commentary on the potential use and abuse of Tβ4 in sport and exercise science.

That is essentially the list. Beyond the two 2003 papers there is no published pharmacology of the fragment, no pharmacokinetics in any species other than the horse, no toxicology, and no head-to-head comparison against full-length Tβ4 in a tendon, cardiac or corneal model. Recent preprints and reviews that discuss “TB-500” draw their biological content from Tβ4 studies.

The human evidence for TB-500

There is none. We could find no clinical trial of the acetylated heptapeptide registered on ClinicalTrials.gov or published in a peer-reviewed journal. Every human study in the table above used the full-length protein under a pharmaceutical sponsor, with placebo controls and safety monitoring. Nothing equivalent exists for TB-500, so claims about its effects, safety or tolerability in people rest on no published evidence.

What this means for a research design

For laboratory work with TB-500, the state of the literature has practical consequences.

• Treat Tβ4 as a comparator, not a proxy. If a hypothesis comes from a Tβ4 paper, run the fragment alongside the full-length protein in the same assay rather than assuming equivalence.
• Start with an in-vitro actin-binding or migration readout. Van Troys’ mapping predicts the fragment binds actin weakly or not at all, while Philp’s 2003 data suggest it retains activity in endothelial migration assays. Those are well-defined, inexpensive first experiments, and reconciling them is an open question.
• Measure degradation. The equine metabolite data show the fragment is metabolised in vivo. Measure stability in culture medium or serum rather than assuming it.
• Confirm the molecule before anything else. With two different compounds sold under one name, the batch report must show an observed mass near 889 Da for the fragment or near 4,963 Da for the protein. Our article on identity testing by HPLC and mass spectrometry explains why HPLC alone cannot settle this.
• Control for the salt. Synthetic short peptides are usually supplied as TFA or acetate salts, and net peptide content varies. See TFA salt peptides.

How to check a TB-500 batch

Because TB-500 is unlicensed, no regulator checks what is sold under the name. The batch laboratory report is the only evidence of what is in the vial, and for this peptide identity matters more than usual. Check:

• The batch number matches the vial label.
• The stated sequence. It should say Ac-LKKTETQ (or Tβ4 17–23) for the fragment. A report that says only “TB-500” or “Thymosin Beta-4” without a sequence has not identified the material.
• Identity is confirmed by mass spectrometry, with an observed mass consistent with about 889 Da for the acetylated heptapeptide. A mass near 4,963 Da means the vial contains full-length Tβ4, whatever the label says.
• Purity is reported as an HPLC area percentage, and you read it as a separation result rather than a statement of content or sterility.
• Method, date and report reference are stated so the report can be verified with the laboratory.

Thistle publishes the laboratory report for the current TB-500 batch on the product page, and any batch can be checked on our batch report lookup. For the method, see How to read a peptide COA and What does 99% purity actually mean?

Thistle supplies TB-500 — 10mg Research Peptide at £34.99, and BPC-157 + TB-500 — 10mg Research Blend at £29.99, each with a batch laboratory report. TB-500 is also a component of two multi-peptide blends, GLOW — 70mg Research Blend at £69.99 and KLOW — 80mg Research Blend at £84.99; our GLOW and KLOW articles explain how the batch report for a multi-peptide vial should be read.

Is TB-500 legal in the UK?

TB-500 has no UK marketing authorisation as a medicine and is not a controlled drug under the Misuse of Drugs Act 1971. It is supplied as a research material for laboratory use. Presentation matters: in April 2026 the MHRA said that where clinics make medicinal claims for peptide injections, those products will be treated as medicines under the Human Medicines Regulations 2012. That is why Thistle describes what has been studied and makes no claims about treating, preventing or improving any condition.

In sport, the World Anti-Doping Agency Prohibited List names “Thymosin-β4 and its derivatives, e.g., TB-500” by name under S2.3, growth factors and growth factor modulators, on the 2026 list in force from 1 January 2026. The prohibition applies at all times, in and out of competition, and covers both the fragment and the parent protein. TB-500 is also prohibited in horse racing, which is where the detection methods above came from.

This section is general information, not legal advice.

Storage and handling

TB-500 is supplied as a lyophilised powder in a sealed vial. Keep it sealed, dry and protected from heat and light, and follow the vial label and batch documentation. Short peptides are generally stable as a dry powder but degrade in solution. See our peptide storage guide.

TB-500 FAQs

Is TB-500 the same as thymosin beta-4?

No. Thymosin beta-4 is a 43-amino-acid protein. TB-500 is a synthetic seven-residue fragment of it, residues 17 to 23, with an acetyl group added. Some vendors sell full-length Tβ4 under the TB-500 name, so the batch report has to state which molecule is in the vial.

Has TB-500 been tested in humans?

No. There are no registered or published clinical trials of the seven-residue fragment. Full-length Tβ4 has been tested in randomised, placebo-controlled trials for dry eye and neurotrophic keratitis, with primary endpoints repeatedly missed and no approval to date.

Why is TB-500 called a “healing peptide”?

Because full-length Tβ4 accelerated wound closure in rat skin, mouse cornea and mouse heart models. Those results belong to the parent protein; the only fragment data are two 2003 papers from the same group, never independently replicated. Our article on tissue signalling peptides looks at how the term outran the evidence.

How does TB-500 differ from BPC-157?

They are unrelated peptides. BPC-157 is a 15-residue sequence from a gastric protein with a large rodent literature of its own; TB-500 is a fragment of a human actin-binding protein with almost no literature of its own. See BPC-157 vs TB-500.

How much does TB-500 cost in the UK?

Prices vary by supplier. At the time of writing, Thistle sells TB-500 10mg at £34.99. Price says nothing about content, purity or even which molecule is in the vial, so check the batch report whichever supplier you use.

Sources

• Van Troys M, Dewitte D, Goethals M, Carlier MF, Vandekerckhove J, Ampe C. The actin binding site of thymosin beta 4 mapped by mutational analysis. The EMBO Journal. 1996;15(2):201–210. Maps actin binding to residues 1–16 and the 17–22 motif.
• Malinda KM, Sidhu GS, Mani H, et al. Thymosin beta4 accelerates wound healing. Journal of Investigative Dermatology. 1999;113(3):364–368. Rat full-thickness wound model; full-length Tβ4.
• Sosne G, Szliter EA, Barrett R, Kernacki KA, Kleinman H, Hazlett LD. Thymosin beta 4 promotes corneal wound healing and decreases inflammation in vivo following alkali injury. Experimental Eye Research. 2002;74(2):293–299. Mouse model.
• Philp D, Huff T, Gho YS, Hannappel E, Kleinman HK. The actin binding site on thymosin β4 promotes angiogenesis. The FASEB Journal. 2003;17(14):2103–2105. And Philp D, Badamchian M, Scheremeta B, et al. Thymosin β4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged mice. Wound Repair and Regeneration. 2003;11(1):19–24. The only published biology of the seven-residue motif peptide.
• Bock-Marquette I, Saxena A, White MD, DiMaio JM, Srivastava D. Thymosin β4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004;432(7016):466–472. Mouse coronary ligation model. And Smart N, Bollini S, Dubé KN, et al. De novo cardiomyocytes from within the activated adult heart after injury. Nature. 2011;474(7353):640–644. Mouse model; Tβ4 priming of epicardial progenitors.
• Goldstein AL, Hannappel E, Kleinman HK. Thymosin β4: actin-sequestering protein moonlights to repair injured tissues. Trends in Molecular Medicine. 2005;11(9):421–429. Review.
• Sosne G, Ousler GW. Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, Phase II clinical trial conducted using the controlled adverse environment (CAE) model. Clinical Ophthalmology. 2015;9:877–884. 72 participants; primary endpoints not met.
• ClinicalTrials.gov. NCT05555589: Safety and efficacy of 0.1% RGN-259 ophthalmic solution for neurotrophic keratopathy (SEER-2). ReGenTree; phase 3; 70 participants. See also FN News, 26 August 2026, on SEER-2 completing its last patient visit with topline results expected in November 2026; Ophthalmology Times, 1 July 2025, on the SEER-3 primary endpoint miss; and RegeneRx, 22 August 2022, on the ARISE trials, the February 2022 FDA pre-BLA meeting and SEER-1.
• ClinicalTrials.gov. NCT00311766: Thymosin beta 4 in the treatment of patients with epidermolysis bullosa (RGN-137). RegeneRx; phase 2; 30 participants; terminated. Follow-on trial NCT03578029 (Lenus Therapeutics; 4 participants; terminated 2021). And NCT04555824: Phase 1a single-dose study of recombinant human thymosin β4 in healthy volunteers. Beijing Northland Biotech; 54 participants; completed 2018. See also RegeneRx, final clinical results from phase I trial with RGN-352, 9 December 2009; 80 volunteers. Full-length protein, safety and pharmacokinetics only.
• Ho ENM, Kwok WH, Lau MY, et al. Doping control analysis of TB-500, a synthetic version of an active region of thymosin β4, in equine urine and plasma by liquid chromatography–mass spectrometry. Journal of Chromatography A. 2012;1265:57–69.
• Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P. 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.
• Davison GW, Brown S. The potential use and abuse of thymosin beta 4 in sport and exercise science. Journal of Sports Sciences. 2013;31:917–918.
• World Anti-Doping Agency. Prohibited List 2026. S2.3 growth factors and growth factor modulators: “Thymosin-β4 and its derivatives, e.g., TB-500”.
• Aesthetics Journal. MHRA investigates clinics following peptide claims. 15 April 2026.

Published by Thistle BioLabs, a UK supplier of research materials. This article summarises external research, not studies conducted by Thistle. Educational information only; no medical advice or recommendation for personal use.