TB-500 vs Thymosin Beta-4: What the Research Does and Does Not Show

LynxLab · 24 October 2026 · 8 min read

How TB-500 differs from the full thymosin beta-4 protein, what the LKKTETQ fragment was shown to do in the lab, and which trial results apply to it.

Photo: CDC, Unsplash

Most writing about TB-500 quotes thymosin beta-4 research as if the two were the same molecule. They are not. Thymosin beta-4 is a 43-amino-acid protein found in almost every human cell, while tb-500 is a synthetic copy of seven of those amino acids with an acetyl group bolted onto one end.

That difference decides which studies you can fairly cite. This post sets out what the fragment itself was shown to do, what the full protein did in human trials, and where the gap between the two sits in October 2026.

Thymosin beta-4 has 43 amino acids, TB-500 has seven

Thymosin beta-4 (written Tβ4 in the literature) is a 5 kDa polypeptide and the most abundant member of the beta-thymosin family in mammalian tissue. Its day job is to hold on to single actin molecules, which is why it is called the main G-actin sequestering peptide (Philp et al., FASEB Journal, 2003).

Inside that chain, residues 17 to 23 spell LKKTETQ: leucine, lysine, lysine, threonine, glutamate, threonine, glutamine. The six-letter core LKKTET is the actin-binding site.

TB-500 is that seven-residue segment made synthetically, with an acetyl group on the N-terminal leucine. The Ghent University doping laboratory identified Ac-LKKTETQ as the active content of a commercial TB-500 product in 2012 using high-resolution mass spectrometry (Esposito et al., Drug Testing and Analysis, 2012). The Hong Kong Jockey Club's racing laboratory reached the same answer the same year.

So when a shop lists tb500 and describes it as "the active region of thymosin beta-4", that is the claim being made: seven amino acids out of 43, with one chemical modification.

What the LKKTETQ fragment was shown to do in 2003

The best evidence that the fragment matters on its own comes from Deborah Philp and Hynda Kleinman's group at the US National Institutes of Health. Using natural thymosin beta-4, proteolytic fragments and synthetic peptides, they found that the seven-amino-acid actin-binding motif was essential for the protein's angiogenic activity.

In migration assays with human umbilical vein endothelial cells and vessel-sprouting assays with chick aortic arches, the whole protein and the seven-residue motif showed near-identical activity at around 50 nM. Peptides lacking any part of the motif were inactive, and adding 5 to 50 nM soluble actin blocked the effect (Philp et al., 2003).

The same paper included an animal experiment. In 26-month-old mice with 3 mm punch wounds, topical thymosin beta-4 at 0.1% and the non-acetylated LKKTETQ peptide at 0.01% both increased epidermal closure and collagen content at day 7, as summarised in the FDA's 2026 review of the substance.

Two points about that study matter for anyone reading about tb-500 for research. The fragment tested was not acetylated. And the FDA noted the study had no dose-response arm, so it cannot say how much fragment is needed for how much effect.

Why the acetyl group is not a footnote

Acetylation changes a peptide's charge, hydrophobicity and size, and with them its stability, folding and binding. The FDA's pharmacology reviewers put it bluntly in May 2026: the profile of the non-acetylated heptapeptide "cannot be directly extrapolated" to TB-500 (FDA briefing document, Pharmacy Compounding Advisory Committee, July 2026).

The one direct test of TB-500 itself is not encouraging for the shortcut. A Korean doping-control group incubated confluent fibroblasts with scratch wounds in TB-500 at 50 µg/mL for eight hours. Closure was no different from vehicle. The metabolite Ac-LKKTE, with two residues clipped off, did produce a small but significant effect (Rahaman et al., Journal of Chromatography B, 2024).

That study also lacked a concentration-response analysis, so it is one data point, not a verdict. But it means the honest position is that TB-500's own activity in a wound model is unproven, and may depend on being broken down into something else first.

The acetyl group does do one job well. In both horse liver homogenate and human liver fractions, TB-500 was cleaved only from the C-terminal end; the acetylated leucine protected the N-terminus (WADA-funded research project 13D34PV, Ghent University). That is why doping laboratories look for a family of acetylated fragments rather than the parent peptide alone.

What the thymosin beta-4 trials actually found

The full protein has a real clinical record, and it belongs to the protein, not the fragment.

In a rat full-thickness wound model, topical or intraperitoneal thymosin beta-4 increased re-epithelialisation by 42% at day 4 and up to 61% at day 7 over saline (Malinda et al., Journal of Investigative Dermatology, 1999).
In mice with a ligated coronary artery, thymosin beta-4 activated integrin-linked kinase and Akt, improved early myocyte survival and improved cardiac function (Bock-Marquette et al., Nature, 2004).
RegeneRx ran a randomised, double-blind phase 2 trial of thymosin beta-4 gel at 0.01%, 0.02% and 0.1% in 72 patients with pressure ulcers between 2006 and 2008 (NCT00382174, ClinicalTrials.gov). A 2021 review of the phase 2 programme in pressure and venous ulcers reported 143 patients in total and healing accelerated "by almost a month" in those who did heal (Xing et al., Frontiers in Endocrinology, 2021).
The eye-drop formulation RGN-259 (0.1% thymosin beta-4) completed a small US phase 3 in neurotrophic keratopathy: 6 of 10 treated patients healed completely at four weeks against 1 of 8 on placebo, p = 0.0656 (Sosne et al., International Journal of Molecular Sciences, 2023).

The European phase 3 of the same eye drop, SEER-3, missed its primary endpoint in June 2025; the company blamed an unusually strong placebo response (Ophthalmology Times, July 2025). A further US phase 3, SEER-2, finished recruiting in July 2026 and had not reported as of this writing.

What that evidence does not say about TB-500

Every item in the list above used the 43-amino-acid protein, recombinant or synthetic, applied as a gel, eye drop or injection in a controlled trial. None used Ac-LKKTETQ.

The FDA searched PubMed, Embase and ClinicalTrials.gov in 2025 and 2026 and "did not identify data, such as clinical studies, on the use of TB-500 in humans". Its adverse-event database held no TB-500 reports through 26 March 2025, which the agency was careful to say is not evidence of safety, only of silence.

For a UK reader comparing tb-500 uk listings with headlines about thymosin beta-4 eye drops, the correct reading is this: the parent protein has reached phase 3 twice and has not yet been licensed anywhere; the fragment has been studied in cells, rats and horses, and never in a human trial.

The racing and anti-doping side of the story, including how the Hong Kong laboratory first confirmed TB-500 in horses, is covered in our post on TB-500 in sport and horse racing.

Where TB-500 stands with regulators in late 2026

TB-500 is not a licensed medicine in the UK, the EU, the US, Canada or Australia. The FDA's review listed no approved products in any of those jurisdictions and no entry in the European or Japanese pharmacopoeias.

In the US it was nominated for the list of bulk substances that compounding pharmacies may use. FDA staff recommended against adding it, citing the absence of human data and the immunogenicity risk of an injected peptide. On 23 July 2026 the advisory committee nonetheless voted narrowly in favour of allowing compounding of TB-500 and several other peptides; the agency is not bound by that vote and had not issued a final rule at the time of writing (BBC News, 23 July 2026).

In sport it is prohibited. The 2026 WADA list names "Thymosin-β4 and its derivatives e.g. TB-500" under S2.3, growth factors and growth factor modulators (WADA Prohibited List).

In the UK it is sold for laboratory research only. LynxLab stocks tb-500 5mg for research use at £23.99 a vial, tested to 99% purity with the batch certificate of analysis on the product page.

Frequently asked questions

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

No. Thymosin beta-4 is a 43-amino-acid protein. TB-500 is a synthetic copy of residues 17 to 23 (LKKTETQ) with an acetyl group on the N-terminus, as identified by the Ghent and Hong Kong doping laboratories in 2012.

Has TB-500 been tested in humans?

Not in any published clinical trial. The FDA's 2026 review found no human studies of TB-500 by any route. The human trials people cite, in pressure ulcers and neurotrophic keratopathy, used the full thymosin beta-4 protein.

Does the LKKTETQ fragment do anything on its own?

In 2003 the non-acetylated fragment matched the whole protein in endothelial migration and vessel-sprouting assays at about 50 nM, and improved wound closure in aged mice. The acetylated version sold as TB-500 showed no effect in a 2024 fibroblast scratch assay, so the question is open.

Can I buy TB-500 in the UK?

Yes, for laboratory research. Researchers can buy tb-500 in 5mg vials from UK stock; it is not a licensed medicine and is on the WADA prohibited list for athletes.

Sources

Research use only

TB-500 from LynxLab

5mg vials from £23.99. ≥99% purity, lab report on the page. Same-day dispatch, UK stock.

Buy TB-500