TB-500 is a synthetic chain of seven amino acids. It copies residues 17 to 23 of thymosin beta-4, a 43-residue protein found in most cells, and carries an acetyl group at the N-terminus.3
The important thing to know when reading about it is that almost every study with "thymosin beta-4" in the title used the full protein, not this fragment. The fragment's own literature is small and mostly about detecting it in doping control.
7 of 43
889.0 g/mol
0
S2.3
Identity
The seven residues run from leucine to glutamine, with the N-terminal amine blocked by an acetyl group. Position numbers below are those of the parent protein.
Fig. 1 · Sequence map. N-terminus acetylated. Numbering follows thymosin beta-4.
This stretch is the part of thymosin beta-4 that binds actin, which was mapped by changing residues one at a time in the 1990s.2 The fragment was first described as a product in its own right in a 2012 paper that made it in the lab to confirm what was being sold under the name TB-500.3
The parent protein
Thymosin beta-4 was first sequenced from calf thymus in 1981.1 It is one of the most abundant small proteins inside cells, where it holds actin monomers in reserve, and it is released from platelets at wound sites. Because it is a natural protein, much of the research tests it directly rather than any fragment.
| Thymosin beta-4 | TB-500 | |
|---|---|---|
| Length | 43 residues | 7 residues |
| Origin | Natural, in most human cells | Synthetic copy of residues 17–23 |
| Studied in | Animals and people | Mostly analytical chemistry and racehorse doping control |
| Approved anywhere | No | No |
What the studies measured
Each row names the molecule actually used. Rows for the full protein do not show that the fragment would do the same.
| Area | Molecule | Model | What was measured | Source |
|---|---|---|---|---|
| Skin | Full protein | Full-thickness wounds in rats; keratinocytes in culture | Wound closure, re-epithelialisation, cell migration | [5] |
| Heart | Full protein | Coronary artery ligation in mice; cardiomyocyte culture | Cell survival, scar size, cardiac function, ILK signalling | [6] |
| Eye | Full protein | People with neurotrophic keratopathy; dry eye | Corneal defect healing, signs and symptoms | [7] |
| Actin binding | Protein and fragment | Purified actin in vitro | Which residues are needed to bind actin | [2] |
| Detection | Fragment | Horse urine and plasma | How to find TB-500 and its breakdown products | [4],[8] |
Human trials
No human study of TB-500 itself has been published. The full protein has been tested as an eye drop by one sponsor.
| Year | Trial | Molecule | Design | People | Source |
|---|---|---|---|---|---|
| 2021 | ARISE-3, dry eye | Tβ4 0.1% eye drop | Phase 3, placebo-controlled. Results in a company release, not a full paper | ~1,500 across three trials | [9] |
| 2023 | Neurotrophic keratopathy | Tβ4 0.1% eye drop | Phase 3, placebo-controlled, double-masked. Authors linked to the sponsor | 18 | [7] |
Regulatory and sport status
As of this revision. General information, not legal advice.
| Where | Status |
|---|---|
| UK and EU | No marketing authorisation. Not a controlled drug in the UK. May not be supplied or promoted for human use. |
| US | Not FDA-approved. |
| Australia | Thymosin beta-4 and TB-500 are not approved by the TGA.10 |
| Sport | Prohibited at all times. Named in WADA class S2.3, growth factors and growth factor modulators: "thymosin-β4 and its derivatives e.g. TB-500".11 |
Open questions
- Whether the seven-residue fragment does in tissue what the full protein does. The binding studies say it holds actin; no published animal study tests the fragment on wounds, heart or cornea.
- How long the fragment lasts in the body. Its half-life and breakdown have been studied only as far as doping-control labs need to find it.
- Whether pairing it with BPC-157 adds anything. No study has tested the two together.
Common questions
Is TB-500 the same as thymosin beta-4?
No. Thymosin beta-4 is a 43-residue protein. TB-500 copies seven of those residues with an acetyl cap. Nearly all published research is on the full protein.
Is TB-500 banned in sport?
Yes. The WADA Prohibited List names thymosin beta-4 and its derivatives, giving TB-500 as the example, in class S2.3. That applies in and out of competition.
Why is it called TB-500?
The name came from the product, not from a lab. Chemists later made the fragment to confirm what was being sold under that name.
How is it different from BPC-157?
Different parent, different size, different evidence. BPC-157 has a large animal literature of its own; TB-500 borrows its reputation from the full protein. See the comparison.
See also
References
- Low TL, Hu SK, Goldstein AL. Complete amino acid sequence of bovine thymosin beta 4. Proc Natl Acad Sci USA. 1981;78(2):1162–1166.
- Van Troys M, et al. The actin binding site of thymosin beta 4 mapped by mutational analysis. EMBO J. 1996;15(2):201–210.
- Esposito S, Deventer K, Goeman J, 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 Test Anal. 2012;4(9):733–738. PMID 22962027
- Ho ENM, et al. Doping control analysis of TB-500, a synthetic version of an active region of thymosin β4, in equine urine and plasma. J Chromatogr A. 2012. PMID 23084823
- Malinda KM, et al. Thymosin beta4 accelerates wound healing. J Invest Dermatol. 1999;113(3):364–368. PMID 10469335
- Bock-Marquette I, et al. Thymosin β4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004;432:466–472. PMID 15565145
- Sosne G, et al. 0.1% RGN-259 (thymosin β4) ophthalmic solution promotes healing and improves comfort in neurotrophic keratopathy patients in a randomized, placebo-controlled, double-masked phase III clinical trial. Int J Mol Sci. 2023;24(1):554.
- Kwok WH, et al. Doping control analysis of seven bioactive peptides in horse plasma by liquid chromatography–mass spectrometry. Anal Bioanal Chem. 2013;405(8):2595–2606.
- RegeneRx Biopharmaceuticals. ReGenTree reports results from ARISE-3 trial of RGN-259 in dry eye. Press release, 14 May 2021.
- Sport Integrity Australia. Thymosin beta-4. sportintegrity.gov.au
- World Anti-Doping Agency. The 2026 Prohibited List, class S2.3. wada-ama.org
Peptidarium Library. TB-500 (entry 0002), revision 1.0, 2 November 2026. peptidarium.com/library/tb-500
Revision history
| Rev | Date | Change | By |
|---|---|---|---|
| 1.0 | 2 Nov 2026 | Entry created. | [Scientific editor] |
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