TB-500 is not thymosin beta-4. Analysis of the product sold under that name found a seven amino acid fragment, not the 43 amino acid protein the research is about. It holds no UK medicines authorisation, it is not a permitted supplement, and it is banned in sport at all times. This article gives no dose, and explains why none exists.
What is TB-500?
Thymosin beta-4 is a real and well studied human protein. It is 43 amino acids long, built from the same twenty amino acids as every other protein in the body, it is one of the most abundant peptides inside cells, and its day job is binding G-actin, the protein subunit that cells assemble and disassemble to change shape and move. Because wound repair is largely a story of cells migrating into a gap, anything that governs actin turnover ends up involved in healing, inflammation and blood vessel growth.
TB-500 is the name of a product, not of a molecule. It appeared first in veterinary and equine circles, where it was used to speed recovery in racehorses, and moved from there into human sport and then into consumer peptide shops. Sellers describe it as a synthetic version of thymosin beta-4, or as its active fragment, and use the two terms interchangeably.
They are not interchangeable, and that is the single most useful thing to know about this subject.
TB-500 is not thymosin beta-4
In 2012, a group at the doping control laboratory in Ghent did something nobody selling the product had bothered to do. Esposito and colleagues took a commercial TB-500 preparation and ran it through liquid chromatography coupled to high resolution mass spectrometry, then confirmed the result by synthesising the compound themselves.
What they identified was the N-terminal acetylated 17-23 fragment of human thymosin beta-4. In letters, Ac-LKKTETQ. Seven amino acids, acetylated at one end, out of a protein that is 43 amino acids long. They published the finding in Drug Testing and Analysis along with a method for detecting it in plasma and urine, which is why it can now be tested for. The identification was made on an Orbitrap high resolution instrument, then cross-checked against the peptide they built themselves by solid-phase synthesis, which is about as close to certainty as analytical chemistry gets.
WHY THE DISTINCTION DECIDES EVERYTHING
is not
thymosin beta-4
The size difference is not a detail
Seven amino acids against 43. The actin-binding motif is present, the rest of the protein is not, and the rest of the protein is where much of the described activity sits.
The studies are about the other one
Every wound healing, cardiac and angiogenesis paper cited on a TB-500 sales page used full-length thymosin beta-4. None of them tested the fragment being sold.
Behaviour in the body is not transferable
A short acetylated peptide has its own absorption, distribution, half-life and breakdown products. Nothing about the parent protein predicts them.
Content varies between vials
TB-500 is a trade name applied to more than one preparation. Some are sold as the fragment, some as a longer analogue. The label rarely says which.
Two laboratories reached that conclusion independently in the same year. Ho and colleagues at the Hong Kong Jockey Club racing laboratory published their own analysis in the Journal of Chromatography A in 2012, and describe TB-500 in the first line of their abstract as a veterinary preparation. Their wording is unambiguous: the key ingredient of TB-500 is the peptide LKKTETQ with artificial acetylation of the N-terminus, corresponding to residues 17 to 23 of thymosin beta-4.
Everything that follows is written with that gap in mind. When the evidence is about thymosin beta-4, this article says so.
What the research shows, and on what
The thymosin beta-4 literature is genuine, extensive and almost entirely preclinical. Goldstein, Hannappel and Kleinman set out the case in Trends in Molecular Medicine in 2005: an actin-sequestering protein that turns out to promote cell migration, angiogenesis, wound repair and the suppression of inflammation. It is a good review and it describes a molecule worth studying. It does not describe a therapy.
Three studies get cited more than the rest. Each is worth knowing by its model rather than by its headline.
| Study | Model | What it measured | What it does not establish |
|---|---|---|---|
| Malinda et al., 1999 | Rat, full thickness skin wound | Reepithelialisation 42 per cent higher than saline at 4 days, up to 61 per cent at 7 days; contraction at least 11 per cent greater by day 7 | Anything about tendon, human skin, or the fragment sold as TB-500 |
| Bock-Marquette et al., 2004 | Mouse, coronary artery ligation | Thymosin beta-4 formed a complex with PINCH and integrin-linked kinase, activated Akt, improved early myocyte survival and cardiac function | Any human cardiac benefit; no equivalent human trial has been completed |
| Cha, Jeong and Kleinman, 2003 | Mouse B16 melanoma cells in C57BL/6 mice | Cells engineered to overexpress thymosin beta-4 showed increased tumour growth and metastatic potential | That an injected peptide does the same, but it is the reason the safety question is open |
The numbers are worth stating in full, because they are the ones that get compressed. In the rat wound model, reepithelialisation was 42% higher than saline at 4 days and up to 61% higher at 7 days, and treated wounds contracted at least 11% more by day 7. In the mouse heart, the effect followed coronary artery ligation. In the melanoma work, the cells had been engineered to overproduce the peptide rather than given it.
Read that table as a whole and a pattern appears. The healing findings are in rodents. The mechanism is plausible and consistent. And the same biology that closes a wound faster, cell migration plus new blood vessels, is the biology a tumour uses. That is not a scare story, it is the reason a serious clinical programme would have to answer the question before anyone injected this routinely.
HOW A RODENT RESULT BECOMES A PRODUCT CLAIM
Where TB-500 came from: horses
The product was not designed for people, and its history explains most of the confusion around it. Both 2012 analytical papers describe TB-500 as a veterinary preparation, and the Hong Kong study exists because racing regulators needed a way to detect it in horses before human sport had caught up.
Their method targets N-acetylated LKKTETQ and its metabolites in equine urine and plasma, isolated by solid-phase extraction and identified by liquid chromatography coupled to mass spectrometry. The claims they list for the preparation are the same ones you will read on a consumer peptide site in 2026: endothelial cell differentiation, angiogenesis in dermal tissues, keratinocyte migration, collagen deposition and reduced inflammation. Fourteen years on, the marketing copy has not moved.
Human anti-doping followed the same route. The compound went onto the WADA Prohibited List for the 2018 season, and WADA has since funded further work on TB-500 metabolism and on detection limits in urine and plasma. A substance attracts that kind of attention when it is being used, not when it is promising.
What none of that establishes is efficacy. Racing laboratories build detection methods for whatever people are injecting into horses. The existence of a test is evidence of a market, not of a working drug.
What has been tested in humans
The honest answer is close to nothing, and the exception is instructive.
Thymosin beta-4 has been taken into human trials, but as eye drops. Sosne and colleagues published a phase 2 randomised, double-masked, placebo controlled trial in Cornea in 2015 on severe dry eye, including dry eye associated with graft versus host disease. 9 patients were treated at two US sites, six times a day for 28 days, with follow-up at 56 days. Ocular discomfort fell 35.1% against vehicle control, p = 0.0141, and total corneal fluorescein staining fell 59.1%, p = 0.0108.
That programme went further. A phase 3 trial of the same ophthalmic solution, ARISE-3, registered as NCT03937882, enrolled 700 participants and has completed. So the company holding this molecule chose to develop it as an eye drop for dry eye, over more than a decade, rather than as an injection for tendon or muscle repair. That choice is information.
Those are real results. They are also 9 patients in the phase 2 trial, a topical formulation on the surface of the eye, and the full-length protein. Nothing in them transfers to injecting a fragment for a sore Achilles.
For TB-500 itself, the position is simpler. No completed randomised controlled trial in humans exists. There is no published human pharmacokinetic profile, no dose ranging study, no safety database and no clinical endpoint of any kind. The evidence base for the thing people actually buy is empty.
Why this article gives no dosage
Most pages on this subject carry a dosage section. Some give milligrams per week, a loading phase and a maintenance phase, laid out with the confidence of a prescribing guide. It is worth saying plainly where those numbers come from, because it is not where the format implies.
A human dose is established by a sequence: pharmacokinetics in a small number of volunteers, dose escalation to find the tolerated range, then dose ranging against an endpoint in a controlled trial. For TB-500 none of those steps has been published. The figures circulating online are extrapolated from animal experiments by body weight, which is not how human dosing is derived, or copied between forums until they acquire the appearance of a standard.
Publishing such a number here would be inventing an authority that does not exist. There is no validated dosing regimen for TB-500, and a page that prints one is telling you something about itself rather than about the peptide.
The same reasoning applies to sourcing. This article names no supplier and links to none.
Side effects, and the risks nobody can quantify
Sales pages list mild, transient effects: injection site irritation, lethargy for a day, occasional head rush. Those reports come from users, not from monitored studies, and the absence of anything worse in an unmonitored population is not a safety finding. No study capable of detecting an uncommon or delayed harm has been run.
Three specific concerns deserve straight answers rather than reassurance.
- The angiogenesis question. Promoting new blood vessels and cell migration is the described mechanism. It is also what a tumour needs. The mouse melanoma work from Kleinman’s own group in 2003 is the reason this has to be evaluated in anyone with a current or past cancer, and that evaluation has not been published.
- What is in the vial. Supply sits outside the medicines regime, so nothing guarantees identity, purity, sterility or quantity. A certificate of analysis supplied by the seller is not independent verification, and it says nothing about endotoxin or sterility in a product people inject.
- Injecting at home. The practical risk here is banal and real: abscess, cellulitis, injecting into a tendon rather than beside it. It has nothing to do with the peptide and everything to do with the route.
Add to that the interaction question, which cannot be answered at all. There is no human pharmacokinetic data, so nobody can say how TB-500 behaves alongside an anticoagulant, an immunosuppressant or chemotherapy.
Why people stack it with BPC-157
The two are almost always discussed together, and the reasoning offered is that they act on different parts of the same repair process: one on blood vessels and cell migration, the other on the gut and connective tissue. It is a tidy story.
No controlled study has tested the combination in people. There is no trial comparing either peptide with the other, none testing them together, and no pharmacokinetic work on what happens when both are injected. The stack exists because two products sold by the same shops are easier to sell together, and because forum reports are self-selecting: people who felt nothing rarely write it up.
The two also differ in law, which is the part that matters if you are tested. They sit in different sections of the Prohibited List, with different consequences, and the next section sets that out.
Is TB-500 legal in the UK?
Three separate layers, and conflating them is where most of the confusion lives.
THE THREE LAYERS OF ITS UK STATUS
As a medicine, it does not exist
TB-500 holds no marketing authorisation from the MHRA for any indication. No licensed product containing it exists in Great Britain, and it cannot be prescribed on the NHS.
As a supplement, it is not permitted
A synthetic peptide with no history of significant consumption in Great Britain before 1997 requires novel food authorisation. None has been granted, and it carries no entry on the GB nutrition and health claims register, so no health claim may lawfully be made for it.
As a research chemical, it is sold
It is not a controlled drug. UK sites list vials at around 24 pounds for 5 mg, labelled strictly for laboratory research, not for human consumption, medical use or diagnostic purposes, and stating that the product has not been evaluated by the MHRA.
Which is the seller drawing the line, not the law
Under the Human Medicines Regulations 2012, what makes something a medicinal product includes how it is presented and what it is intended for. A research-use label does not settle that question by itself.
Banned in sport, and not in the same class as BPC-157
If you compete under any anti-doping code, this section is the whole article. TB-500 is named on the World Anti-Doping Agency Prohibited List by name, not by inference.
It sits in section S2, peptide hormones, growth factors, related substances and mimetics, which is prohibited at all times, in and out of competition. Within that, subsection S2.3 covers growth factors and growth factor modulators, and the entry reads: thymosin beta-4 and its derivatives, for example TB-500. The list has named it since 2018.
One detail matters for anyone comparing the two peptides people usually stack together. BPC-157 is prohibited under S0, non-approved substances, where everything is a Specified Substance. TB-500 is under S2, where the list states that all prohibited substances in the class are non-Specified Substances. Specified status affects how an anti-doping rule violation is handled and what an athlete has to prove. The two are not equivalent, and a page that treats them as the same regulatory object is wrong on both.
Detection is not theoretical either. The Ghent group published a method for finding Ac-LKKTETQ in plasma and urine in the same 2012 paper that identified it. UK Anti-Doping applies the WADA list in full, and strict liability means an athlete is responsible for what is in their sample regardless of how it got there.
If you are here because a tendon is not healing
Most people reading about TB-500 are not athletes chasing a marginal gain. They have had shoulder, Achilles or elbow pain for eight months, they have tried rest, and rest did not work. That is a real problem and it deserves a real answer rather than a lecture.
The answer that has evidence behind it is unglamorous. Tendons respond to graded mechanical load, not to rest, and the programmes that work are measured in months rather than weeks. A physiotherapist who will progress the load rather than tell you to stop is worth more than anything in a vial. If the diagnosis itself is uncertain, and shoulder and hip pain in particular are often something other than what they look like, that is a GP appointment before anything else.
Around that, the things you can control are sleep, protein intake, smoking and blood glucose, all of which affect connective tissue repair and none of which is banned or unlicensed. If you want nutritional support alongside a loading programme, a supplement formulated for tendon pain is a lawful, characterised product with a known composition, which is precisely what a research peptide is not. For a more general inflammatory background, the same argument applies to a turmeric formulation built for absorption.
Graded loading is worth defining, because rest is the instinct and rest is the mistake. It means putting a controlled, progressive amount of force through the tendon several times a week, at an intensity that provokes a tolerable ache which settles within 24 hours, and increasing it as the tendon copes. Progress is measured in months. Most people who say the exercises did not work stopped at 6 weeks, or never increased the load past the first session.
None of that will feel as decisive as an injection. It is, however, the part of the field where somebody has actually done the trials.
Frequently asked questions
What is TB-500 used for?
It is marketed for tissue repair, tendon and ligament recovery, wound healing and flexibility. None of those uses is authorised anywhere, and no completed randomised trial in humans supports any of them. The underlying research is on thymosin beta-4, in rats and mice.
Is TB-500 the same as thymosin beta-4?
No. Analysis of a commercial TB-500 preparation by mass spectrometry identified the N-terminal acetylated 17-23 fragment of thymosin beta-4, seven amino acids out of 43. The studies people cite used the full-length protein.
Is TB500 better than BPC-157?
Neither has been compared with the other in a controlled human trial, so the question has no evidence-based answer. They differ in regulatory terms: BPC-157 is prohibited in sport under S0 as a Specified Substance, TB-500 under S2.3 as a non-Specified Substance.
What are TB500 side effects?
Users report injection site irritation and short-lived tiredness. No monitored study capable of detecting an uncommon or delayed harm has been run, so a list of side effects would be a list of what nobody has looked for. The open questions are angiogenesis in anyone with a cancer history, and what a research-grade vial actually contains.
Is TB-500 banned in sport?
Yes, at all times, in and out of competition. It is named on the WADA Prohibited List under S2.3, growth factors and growth factor modulators, as thymosin beta-4 and its derivatives, for example TB-500. A detection method for plasma and urine was published in 2012.
Can you buy TB-500 legally in the UK?
UK websites sell it labelled for laboratory research only and not for human consumption. It is not a controlled drug, but it holds no MHRA authorisation and is not a permitted supplement ingredient, and under the Human Medicines Regulations 2012 how a product is presented and intended affects whether it counts as a medicine.
Does TB-500 help tendon injuries?
There is no human evidence that it does. The tendon and ligament claims extrapolate from rodent skin and heart studies on a different molecule. Graded loading under a physiotherapist remains the intervention with actual trial support for persistent tendon pain.
Sources
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 Testing and Analysis, 2012. DOI: 10.1002/dta.1402
Ho E.N.M., Kwok W.H., Lau M.Y., et al. Doping control analysis of TB-500, a synthetic version of an active region of thymosin beta-4, in equine urine and plasma by liquid chromatography-mass spectrometry. Journal of Chromatography A, 2012. DOI: 10.1016/j.chroma.2012.09.043
Goldstein A.L., Hannappel E., Kleinman H.K. Thymosin beta-4: actin-sequestering protein moonlights to repair injured tissues. Trends in Molecular Medicine, 2005. DOI: 10.1016/j.molmed.2005.07.004
Malinda K.M., Kleinman H.K., Sidhu G.S., et al. Thymosin beta-4 accelerates wound healing. Journal of Investigative Dermatology, 1999. DOI: 10.1046/j.1523-1747.1999.00708.x
Bock-Marquette I., Saxena A., White M.D., DiMaio J.M., Srivastava D. Thymosin beta-4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature, 2004. DOI: 10.1038/nature03000
Cha H.J., Jeong M.J., Kleinman H.K. Role of thymosin beta-4 in tumor metastasis and angiogenesis. Journal of the National Cancer Institute, 2003. DOI: 10.1093/jnci/djg100
Sosne G., Dunn S.P., Kim C. Thymosin beta-4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea, 2015. DOI: 10.1097/ICO.0000000000000379
Hannappel E. Thymosin beta-4 and its posttranslational modifications. Annals of the New York Academy of Sciences, 2010. DOI: 10.1111/j.1749-6632.2010.05485.x
Regulatory status checked against the WADA 2026 Prohibited List, section S2.3, and the Great Britain registers held by the Food Standards Agency.
This article is general information, not medical advice, and it is not a recommendation to use TB-500. It gives no dosing regimen because none has been validated. Speak to your GP or a physiotherapist about an injury that is not settling.
