TB-500 is a synthetic peptide derived from thymosin beta-4 (Tβ4), a 43-amino-acid protein found in many of the body’s cells [2]. The PubChem database lists TB-500 as a short fragment of that protein: seven amino acids with an N-terminal acetyl group and a molar mass of 889.0 g/mol [1]. Commercially, however, the name TB-500 is not always used in this sense; sometimes it refers to fully synthetic Tβ4. Research on Tβ4 is largely preclinical, and WADA prohibits Tβ4 and its derivatives, such as TB-500, in sport [5].
Thymosin beta-4: the natural protein
Thymosin beta-4 is encoded by the TMSB4X gene. The protein is synthesised as a 44-amino-acid chain; the first amino acid (methionine) is then removed, leaving 43. The new N-terminal residue, a serine, carries an acetyl group [2]. PubChem gives Tβ4 the formula C212H350N56O78S and a molar mass of about 4963 g/mol [1].
The best-known function of Tβ4 relates to the cytoskeleton, the internal ‘scaffolding’ of the cell. Tβ4 binds individual actin molecules (G-actin) and sequesters them, making them less likely to assemble into actin filaments [2]. According to a 2012 review, Tβ4 is released from platelets and macrophages, among other cells, and is involved in cell migration [3]. A small four-amino-acid peptide, Ac-SDKP, can also be cleaved from the N-terminus of the protein; it has a role of its own in blood cell formation [2].
TB-500: fragment or full-length protein
In PubChem, TB-500 is the compound Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH, or Ac-LKKTETQ for short [1]. These seven amino acids correspond to positions 17 to 23 of mature Tβ4. This stretch lies in the region of the protein that mutation studies have shown to be important for actin binding [2].
| Thymosin beta-4 (Tβ4) | TB-500 according to PubChem | |
|---|---|---|
| Number of amino acids | 43 | 7 (Ac-LKKTETQ) |
| Molecular formula | C212H350N56O78S | C38H68N10O14 |
| Molar mass | approx. 4963 g/mol | 889.0 g/mol |
| PubChem CID | 45382195 | 62707662 |
| CAS number | not listed | 885340-08-9 |
In practice, the names are used interchangeably. Under the name ‘TB-500’ you may come across either the short fragment or fully synthetic Tβ4, including in product descriptions. These are two different substances. The quickest way to tell them apart is the mass spectrometry result on the certificate of analysis: a measured mass of around 889 points to the fragment, and a mass of around 4963 to the full-length protein. If the certificate states neither sequence nor mass, you cannot be sure which form you have. For more on reading such a certificate, see How to read a certificate of analysis (COA).
Small details matter too. The N-terminal acetyl group makes the molecule about 42 g/mol heavier than the same chain without it, so a mass that differs by exactly that amount may mean the acetyl group is missing. The two forms also differ in terms of storage: full-length Tβ4 contains a methionine, an amino acid that is sensitive to oxidation, whereas the fragment contains glutamine, which can deamidate in solution. How to take this into account is explained in Storing peptides.
What has been studied
Most research concerns full-length Tβ4, not the short fragment. Tβ4 has been studied in cell cultures and in animal models of tissue repair in tissues including the skin, eye, heart and brain [3]. Phase 2 studies have also been carried out in people with chronic skin wounds, such as pressure ulcers [4]. This means that Tβ4 has reached an early stage of clinical research; it does not mean that it has been approved as a medicine.
Two caveats apply. First, results obtained with the full-length protein cannot simply be extrapolated to a seven-amino-acid fragment; these are chemically and biologically different molecules. Second, phase 2 studies are designed to provide initial indications, not large-scale evidence of efficacy or safety. The sources discussed here contain no data on long-term exposure in humans.
Status with regulators and WADA
- Not an approved medicine. As far as we know, no medicine containing Tβ4 or TB-500 holds a marketing authorisation in the European Union. What this means for research material is explained in Research use only (RUO): what does it mean.
- WADA, category S2.3. Under growth factors and growth factor modulators, the 2026 Prohibited List specifically names ‘Thymosin-β4 and its derivatives e.g. TB-500’. Substances in this class are prohibited at all times, in and out of competition [5].
Products
- TB-500 5 mg (freeze-dried, in a vial)
- TB-500 10 mg (freeze-dried, in a vial)
- KLOW 80 mg, a blend of BPC-157, TB-500, GHK-Cu and KPV
Clean Peptides supplies TB-500 as the common research variant sold on the market under that name. The specifications for each strength are on the product pages above. Every vial and pen carries a batch number on the label.
Further reading
- What is BPC-157? The state of the research
- What is GHK-Cu? The copper peptide in research and cosmetics
- What are peptides? Explanation and key terms
- How to read a certificate of analysis (COA): HPLC and MS explained
- Knowledge base: peptides and research materials explained
Sources
- PubChem, National Library of Medicine. TB-500, CID 62707662, and Thymosin Beta 4, CID 45382195. pubchem.ncbi.nlm.nih.gov (accessed 30 September 2026)
- UniProt Consortium. UniProtKB P62328, Thymosin beta-4 (TMSB4X), Homo sapiens. uniprot.org (accessed 30 September 2026)
- Goldstein AL, Hannappel E, Sosne G, Kleinman HK. Thymosin β4: a multi-functional regenerative peptide. Basic properties and clinical applications. Expert Opinion on Biological Therapy 2012;12(1):37–51. doi:10.1517/14712598.2012.634793
- Kleinman HK, Sosne G. Thymosin β4 Promotes Dermal Healing. Vitamins and Hormones 2016;102:251–275. doi:10.1016/bs.vh.2016.04.005
- World Anti-Doping Agency. International Standard Prohibited List 2026 (in force since 1 January 2026), section S2.3. wada-ama.org (accessed 30 September 2026)
For laboratory research use only. Clean Peptides products are not intended for use in humans or animals. This article provides general information and is not medical advice.
