TB-500 and thymosin beta-4: structure, research and regulation

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Prepared by: Research Desk. Sources are linked for verification.

Published 19 October 2026

At a glance

Type: short synthetic peptide (acetylated seven-residue sequence, Ac-LKKTETQ)
Parent protein: thymosin beta-4 (Tβ4), a 43-amino-acid protein found in almost all cells
Research stage: preclinical work on the parent protein; very little published work on TB-500 itself
Regulatory status: not an approved medicine; prohibited in sport by WADA

What TB-500 is

TB-500 is the name used for a synthetic peptide based on the central actin-binding region of thymosin beta-4. Thymosin beta-4 is a small protein of 43 amino acids and is the main actin-sequestering molecule in most animal cells. The sequence LKKTETQ, covering amino acids 17 to 23 of the protein plus one extra residue, was identified as one of its active sites. TB-500 is usually described as the N-acetylated form of that short sequence.

The distinction matters. Much of the research quoted in connection with TB-500 was done with full-length thymosin beta-4, not with the short synthetic fragment.

Research history

Thymosin beta-4 was first characterised in the early 1980s as part of work on thymus extracts led by Allan Goldstein's group. Over the following decades researchers found that it binds monomeric (G-) actin and influences how cells move. A 2010 review by Sosne et al. mapped several functions to short sequences within the protein: the N-terminal Ac-SDKP tetrapeptide, a longer N-terminal fragment, and the central LKKTETQ region associated with cell migration, angiogenesis and wound healing in experimental models.

A 2012 review by Goldstein et al. summarised the basic biology of thymosin beta-4 and the areas where it had been studied, including skin, eye, heart and brain models.

Mechanisms studied in preclinical work

Actin binding. Thymosin beta-4 binds G-actin and regulates how much actin is available to build filaments. This is linked to cell migration in culture.
Cell survival signalling. In a widely cited mouse study, Bock-Marquette et al. (2004) in Nature reported that thymosin beta-4 formed a complex with PINCH and integrin-linked kinase (ILK), leading to activation of the survival kinase Akt in heart muscle cells.
Angiogenesis and inflammation. Different regions of the protein have been associated with blood vessel formation (LKKTETQ region) and with lower inflammation and fibrosis in models (Ac-SDKP).

These findings concern the full protein or specific fragments studied in cells and animals. They do not establish any effect of TB-500 in people.

The published research landscape

Published research on TB-500 as a distinct compound is sparse. A large part of it is analytical and comes from doping-control laboratories, which need to detect the compound and its breakdown products.

Esposito et al. (2015) described in vitro models for studying how small peptide hormones are metabolised, for use in sport drug testing.
Rahaman et al. (2024) developed a method using ultra-high-performance liquid chromatography and high-resolution mass spectrometry to measure TB-500 and its metabolites in vitro and in rats. The authors noted that the biological effects of TB-500 itself had not been documented, and they compared the activity of its metabolites with the parent compound in fibroblast assays.

We found no published randomised controlled trials of TB-500 in humans.

Regulatory status

United States. TB-500 is not an FDA-approved drug. FDA's page on bulk drug substances that may present significant safety risks lists "thymosin beta-4, fragment (LKKTETQ), also known as TB-500" among substances whose category 2 nominations were withdrawn, and states that FDA identified no human exposure data.
Sport. WADA's Prohibited List includes thymosin beta-4 and its derivatives, such as TB-500, under S2 (peptide hormones, growth factors, related substances and mimetics), prohibited at all times.
Elsewhere. We found no marketing authorisation for TB-500 from any major regulator as of 19 October 2026.

Key terms

G-actin. The single-molecule (globular) form of actin, which assembles into filaments that shape and move cells.
Active site. A short stretch of a protein's sequence that carries a specific biological activity.
Metabolite. A smaller molecule produced when the body or an enzyme system breaks down a compound; doping laboratories often test for metabolites.

Limitations of the evidence

Most mechanistic evidence relates to full-length thymosin beta-4, not to the synthetic fragment.
Published work on TB-500 itself is mainly analytical chemistry for doping control.
No controlled human data on TB-500 have been published.

Where researchers source it

Purita is a store that lists TB-500 for laboratory research use only. Its product page carries the label "For Research Use Only. Not for human or animal administration."

Purita product page

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