Peptide Guides
Important
Neither TB-500 nor thymosin beta-4 is an approved medicine in any country. Neither holds a licence from the MHRA in the United Kingdom, the EMA in Europe, or the FDA in the United States. This guide explains the difference between two related molecules. It is not medical advice, and nothing within it constitutes a recommendation to use either one. Products supplied through this site are intended for laboratory research use only.
Quick answer
- No, TB-500 and thymosin beta-4 are not the same thing. Thymosin beta-4 is a natural peptide of 43 amino acids found in almost every cell. TB-500 is a lab-made copy of just seven of those amino acids, with one small chemical change.
- Thymosin beta-4 has been through around twenty years of pharmaceutical trials in people. TB-500 has not: the FDA's 2026 review identified no human exposure data for products containing the fragment.
- Many claims made about TB-500 online rely on findings from studies of full-length thymosin beta-4 rather than studies of the fragment itself.
- WADA prohibits both at all times under the same listing, so the distinction gives a tested athlete nothing.
Are TB-500 and Thymosin Beta-4 the Same?
No. They are related molecules, and they are routinely treated as interchangeable, but one is a small copied piece of the other. Picture thymosin beta-4 as a chain of 43 links. TB-500 is a lab-made copy of seven of those links, the section of the chain that binds actin, with one small chemical change at one end.1 Chemists identify it as the N-terminally acetylated 17-23 fragment of thymosin beta-4, written Ac-LKKTETQ.1 A seven-link copy is not the 43-link chain, and the research record for one is not the research record for the other.
What Thymosin Beta-4 Is
Thymosin beta-4 is a natural peptide of 43 amino acids, one of the most abundant small peptides in human cells. Its main known job is looking after actin, the protein cells use as internal scaffolding, which cells constantly build up and take down as they move, divide and repair themselves. A peptide is a short chain of amino acids, and our introduction to peptides starts from the beginning.
Because cell movement sits at the centre of wound healing, thymosin beta-4 went through a real pharmaceutical development programme. Over about two decades it was tested in people for pressure ulcers, venous leg ulcers, dry eye, a corneal condition called neurotrophic keratopathy, and heart attack recovery.2,3 The results were mixed, no regulator approved a medicine based on it, and several programmes stopped. Those are the trials people usually mean when they call this family of compounds "clinically tested".
What TB-500 Is
TB-500 is a product name, not a molecule name. The preparation it originally described was a veterinary product, and when anti-doping laboratories analysed vials sold under the name, what they found inside was the seven-amino-acid copied section of thymosin beta-4 described above.1,4 What TB-500 is tells the full story, from horse racing to the research market.
When the FDA reviewed TB-500 in 2026, it stated that it had not identified human exposure data for products containing the fragment.5 No published human trial has tested it, and no published human safety study exists; TB-500 side effects covers what that means in practice.
How the Two Became Confused
The fragment was copied from the part of thymosin beta-4 that binds actin, so sellers and forums describe the parent's research as if it belonged to the copy. The parent has two decades of trials, animal studies across wounds, eyes and the heart, and a genuine scientific literature. The copy inherits the reputation without the record.
Nothing about the fragment's size makes it useless to study. It now has animal research of its own, including a 2026 rat tendon study that tested it directly.6 The problem is presenting evidence about one molecule as evidence about a different one.
Why the Distinction Changes the Evidence
| Question | Thymosin beta-4 | TB-500 fragment |
|---|---|---|
| What is it? | Natural peptide, 43 amino acids | Lab-made copy of 7 of those amino acids |
| Found in the body? | Yes, in almost every cell | No, made in a laboratory |
| Human trials? | Around two decades of pharmaceutical trials | None; no identified human exposure data |
| Human safety data? | Limited, short-term, from small trials | None published |
| Approved medicine? | No, anywhere | No, anywhere |
| Animal research? | Extensive | Small but growing, including a 2026 tendon study |
TB-500 has not been through clinical trials; the trials people cite tested full-length thymosin beta-4. Those trials reported no significant adverse events, in small groups over short periods, and small trials of one molecule cannot establish the safety of a different one.
Which Molecule Is in the Vial?
The TB-500 name has not been used consistently in the research-product market. Published analyses of products sold over the internet as TB500 and TB1000 found contents that were not consistent with the products' own descriptions.8 A batch-specific identity test says more than the product name, and that is what a certificate of analysis is for: it reports what a tested sample actually contained, molecule included, rather than what the label implies.
Where the Distinction Makes No Difference
Anti-doping is the one place the difference between the two molecules counts for nothing. The 2026 WADA Prohibited List bans "Thymosin-ß4 and its derivatives e.g. TB-500" under category S2.3, at all times, in and out of competition.7 The listing covers the parent and the fragment together, and validated detection methods are published. A tested athlete gets no room from the chemistry.
Common Questions
Is TB-500 the same as thymosin beta-4?
No. Thymosin beta-4 is a natural 43-amino-acid peptide. TB-500 is a lab-made copy of seven of those amino acids with one small chemical change. They are related, and they are different molecules with different research records.
Has TB-500 been through clinical trials?
No. The clinical trials people cite tested full-length thymosin beta-4. The FDA's 2026 review identified no human exposure data for products containing the TB-500 fragment.5
Is TB-500 stronger or better than thymosin beta-4?
No human study has compared them, and the fragment has no human evidence at all, so the question has no evidence-based answer. The fragment was designed to copy the parent's most active section, and whether that design achieves anything in people has never been tested.
How do I know which molecule a TB-500 product contains?
From the batch certificate of analysis, which reports the tested identity of the contents. The label alone does not settle it, because analyses of products sold under the name have found contents inconsistent with their descriptions.8
TB-500 Research Specification
The current TB-500 research specification is freeze-dried (lyophilised) powder, purity-tested by HPLC with identity confirmed by mass spectrometry, with a dated certificate of analysis published per batch. We publish what each batch contains and make no claims about what it does.
Supplied for laboratory research use only. Not for human consumption.
References
- Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P. 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):733-8. DOI
- Guarnera G, De Rosa A, Camerini R. Thymosin beta-4 and venous ulcers: clinical remarks on a European prospective, randomized study on safety, tolerability, and enhancement on healing. Ann N Y Acad Sci. 2007;1112:407-12. DOI
- Kruoch Z, Choo AY, Kemp A, et al. Medical and surgical interventions for neurotrophic keratopathy. Cochrane Database Syst Rev. 2025;12:CD015723. DOI
- Ho ENM, Kwok WH, Lau MY, et al. 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;1265:57-69. DOI
- US Food and Drug Administration. Pharmacy Compounding Advisory Committee Briefing Document: TB-500. July 2026. FDA briefing document
- Biçer O, Adanir O, Güleryüz Y, et al. Effects of BPC-157 and TB-500 on Achilles tendon healing in rats: a histopathological and biomechanical study. Jt Dis Relat Surg. 2026;37(3):822-837. DOI
- World Anti-Doping Agency. Prohibited List 2026, effective 1 January 2026, category S2.3: Growth Factors and Growth Factor Modulators. WADA
- Delcourt V, Garcia P, Chabot B, et al. TB500/TB1000 and SGF1000: A scientific approach for a better understanding of misbranded and adulterated drugs. Drug Test Anal. 2023;15(4):458-464. DOI