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

PepsRadar claim check · October 8, 2026 · Researched with AI assistance · Not reviewed by a medical professional

The claim

“TB-500 is the same thing as thymosin beta-4 and works the same way.”

Verdict: Not supported

TB-500 is not thymosin beta-4. Lab analyses of TB-500 products found a short, chemically modified piece of the protein, seven amino acids long, while thymosin beta-4 itself has 43. Every published human trial tested the full-length protein, and no human trial of the TB-500 fragment has been published, so there is no human evidence that it works the same way.

No. Thymosin beta-4 is a natural 43-amino-acid protein found in almost every cell. TB-500 is a synthetic copy of one short stretch of it, amino acids 17 to 23, with an extra chemical group added to one end. Lab work suggests this stretch carries part of the full protein's activity, but human trials have only tested the full protein, mainly as eye drops and for heart attacks, and the FDA says it has found no human exposure data for the fragment.

Two different molecules

Thymosin beta-4 is a small protein of 43 amino acids. It is the main molecule cells use to hold actin, a building block of the cell skeleton, in reserve. A 2010 review described several active regions inside it. A four-amino-acid piece at the start (Ac-SDKP) is linked to reduced inflammation and scarring, a longer piece at the start is linked to cell survival, and the central actin-binding stretch around LKKTETQ is linked to cell migration, new blood vessel growth and wound healing.

TB-500 contains only that central stretch. A Belgian anti-doping laboratory identified the active ingredient of a product sold as TB-500 as the 17-23 fragment of thymosin beta-4 with an acetyl group added to its front end (Ac-LKKTETQ). The Hong Kong Jockey Club's racing laboratory described the same thing and noted that the acetylation is artificial. In other words, TB-500 lacks 36 of the protein's 43 amino acids, including the regions linked to anti-inflammatory and cell-survival effects.

Sources: PubMed 20179146 · PubMed 22962027 · PubMed 23084823

What lab and animal studies show about the fragment

The idea that the fragment can stand in for the whole protein comes mainly from a 2003 NIH lab study. Using the natural protein, pieces of it and synthetic peptides, the researchers found that the seven-amino-acid actin-binding motif was needed for the protein's blood-vessel-forming activity. In human endothelial cells and chick artery tissue, the motif and the full protein performed almost identically. These were cell and tissue experiments, not studies in animals or people.

A 2024 Korean doping-control study complicates the picture. TB-500 was broken down into smaller pieces in rats and in lab tests with human serum, and in cultured fibroblasts (connective tissue cells) the intact peptide did not show significant wound-healing activity, while one of its breakdown products did. The authors noted that the biological effects of TB-500 itself had not been documented. A 2026 rat study of surgically repaired Achilles tendons reported better strength and tissue scores with a peptide it called both TB-500 and synthetic thymosin beta-4, which shows how loosely the two names are used even in research papers.

Sources: PubMed 14500546 · PubMed 38382158 · PubMed 42542926

Human trials of the full protein: the eye

Most human data for thymosin beta-4 come from eye drops called RGN-259, which contain the full-length protein. In a small phase 2 trial in nine patients with severe dry eye, the drops reduced eye discomfort and corneal staining, a sign of surface damage, compared with a vehicle solution. A larger 72-person phase 2 trial using a controlled dry-environment model did not meet either of its main goals, although some secondary measures improved.

In a phase 3 trial in 18 patients with neurotrophic keratopathy, a hard-to-heal corneal condition, complete healing at four weeks occurred in 6 of 10 treated patients and 1 of 8 on placebo. That difference fell just short of statistical significance, though other measures favored the drops. The study was designed by employees of ReGenTree, the company developing RGN-259. None of these eye trials tested TB-500.

Sources: PubMed 25826322 · PubMed 26056426 · PubMed 36613994

Human trials of the full protein: the heart

RegeneRx Biopharmaceuticals developed full-length thymosin beta-4 as a possible treatment for acute heart attack, based on laboratory and animal research suggesting that it helped heart muscle cells survive and move. A 2010 phase 1 study gave intravenous synthetic thymosin beta-4 or placebo to 40 healthy volunteers, first as single doses and then daily for 14 days. Side effects were infrequent and mild to moderate, with no serious adverse events.

In China, a recombinant version of the full protein was tested in 96 heart attack patients after their blocked artery was reopened. Infarct size was smaller in a subgroup that received the first dose soon after the procedure, but across the whole trial the difference from placebo was not significant. The authors called for further randomized studies. These results apply to the full protein given under medical supervision, not to the TB-500 fragment.

Sources: PubMed 17947592 · PubMed 20536472 · PubMed 41229390

No published human trials of TB-500

We searched PubMed for human studies of TB-500 and its chemical name (Ac-LKKTETQ) and found none. The FDA reached a similar conclusion. In its list of bulk drug substances that may present significant safety risks in compounding, it states that it has not identified any human exposure data for thymosin beta-4 fragment (LKKTETQ), also known as TB-500. The agency adds that the fragment may carry a risk of immune reactions because of aggregation and peptide-related impurities.

A 2026 review in Sports Medicine listed TB-500 separately from thymosin beta-4 and concluded that, for unapproved peptides as a group, rigorous human safety data are scarce despite favorable animal results. So the claim that TB-500 works the same way as thymosin beta-4 has simply never been tested in people.

Sources: fda.gov · PubMed 41966639

Product quality and sport rules

Because TB-500 is sold outside normal drug regulation, what is in the vial is uncertain. A 2023 analysis by a French horse-racing laboratory of products sold online as TB500 and TB1000 found that their contents did not consistently match how the products had been described. Racing laboratories have developed specific tests to detect the fragment and its breakdown products in horses.

The World Anti-Doping Agency lists thymosin beta-4 and its derivatives, naming TB-500 as an example, among growth factors that are prohibited at all times. That listing groups the two together for doping purposes, but it is a rule about banned substances, not evidence that they act the same way.

Sources: PubMed 36482504 · PubMed 23084823 · wada-ama.org

Profiles

TB-500 profile → · Thymosin beta-4 profile →

References

Biological activities of thymosin beta4 defined by active sites in short peptide sequences. FASEB J · 2010 · PMID 20179146
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 · PMID 22962027
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. J Chromatogr A · 2012 · PMID 23084823
The actin binding site on thymosin beta4 promotes angiogenesis. FASEB J · 2003 · PMID 14500546
Simultaneous quantification of TB-500 and its metabolites in in-vitro experiments and rats by UHPLC-Q-Exactive orbitrap MS/MS and their screening by wound healing activities in-vitro. J Chromatogr B Analyt Technol Biomed Life Sci · 2024 · PMID 38382158
Effects of BPC-157 and TB-500 on Achilles tendon healing in rats: A histopathological and biomechanical study. Jt Dis Relat Surg · 2026 · PMID 42542926
Thymosin β4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea · 2015 · PMID 25826322
Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, Phase II clinical trial conducted using the controlled adverse environment (CAE™) model. Clin Ophthalmol · 2015 · PMID 26056426
0.1% RGN-259 (Thymosin ß4) 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 · 2022 · PMID 36613994
Development of thymosin beta4 for treatment of patients with ischemic heart disease. Ann N Y Acad Sci · 2007 · PMID 17947592
A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. Ann N Y Acad Sci · 2010 · PMID 20536472
Recombinant human thymosin beta 4 improves ischemic cardiac dysfunction in mice and patients with acute ST-segment elevation myocardial infarction after reperfusion. Cardiovasc Res · 2025 · PMID 41229390
Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance. Sports Med · 2026 · PMID 41966639
TB500/TB1000 and SGF1000: A scientific approach for a better understanding of misbranded and adulterated drugs. Drug Test Anal · 2023 · PMID 36482504

Other sources

These are original summaries of published research, written with AI assistance and checked against the cited sources. They are not medical advice and have not been reviewed by a clinician. Every PubMed reference was checked against PubMed's record for title, year and journal. All claim checks · Editorial standards