TB-500
Also known as TB500, TB 500, Ac-LKKTETQ, TB-500 acetate, thymosin beta-4 fragment 17-23
A seven-amino-acid fragment of thymosin beta-4, not the protein itself. No study has reported giving it to a human being.
TB-500 is a synthetic peptide of seven amino acids, LKKTETQ with an acetyl group added at one end. That sequence is residues 17 to 23 of thymosin beta-4, a 43-amino-acid protein found throughout the body, and it is the part of that protein which binds actin.
It is not thymosin beta-4
This distinction decides what the rest of the page can say, and it is the one most often lost. Vendors and articles routinely describe TB-500 as a synthetic version of thymosin beta-4 and use the two names interchangeably. FDA addresses this directly and states that thymosin beta-4 and TB-500 are not the same substance. The seven-residue acetylated peptide was identified in a marketed TB-500 product by mass spectrometry in 2012, so this is a measured fact about what is in the vial rather than a labelling opinion.
The consequence is that research on thymosin beta-4 is not research on TB-500. Thymosin beta-4 does have its own clinical programme: a ClinicalTrials.gov search on 2 October 2026 returned 18 records, of which 17 concern thymosin beta-4 itself and the eighteenth is the TB-500 trial described below. They are in dry eye, neurotrophic keratopathy, acute myocardial infarction, venous and pressure ulcers and epidermolysis bullosa. None is in tendon, muscle or ligament, which is what TB-500 is sold for.
That programme should not be read as validation either. Its two largest trials, ARISE-3 with 700 participants and ARISE-2 with 601, tested a thymosin beta-4 eye drop against placebo in dry eye and have posted results. On ARISE-3's two primary measures the posted means are -0.41 for the drug against -0.46 for placebo on inferior corneal staining, and -0.4 against -0.4 on ocular discomfort. No statistical comparison is posted with them, so the right reading is that the registry shows no separation from placebo on either primary measure, not that a published analysis declared the trial a failure.
A second gap sits inside the first one. FDA notes that wound healing is an effect normally associated with the sequence in its unacetylated form, and states that the profile of the unacetylated heptapeptide cannot be directly extrapolated to the acetylated form, because acetylation irreversibly alters a peptide's charge, hydrophobicity and size. The one laboratory test of the acetylated peptide itself found it did not close wounds in cultured fibroblasts, while one of its breakdown products did. The paper reporting that work opens by saying that the biological effects of TB-500 have not been documented.
Two forms are sold under the name, and they are different bulk drug substances: the free base and the acetate salt, the latter about 60 g/mol heavier. Both carry the N-terminal acetyl group that distinguishes the compound from the plain heptapeptide, so that acetyl group is not what the word acetate refers to.
What exists in people
Nothing has been reported. FDA states that after a literature search it found no article in which TB-500 was administered to a human being, and that it found no case reports of its use in people either. A PubMed search restricted to trial and case-report publication types returns nothing relevant.
One trial is registered, and it is not about recovery: NCT07487363, a phase 1 and 2 dose-escalation study of TB-500 in stable atherosclerotic cardiovascular disease, with 80 participants estimated, recruiting since February 2026 and primary completion estimated for February 2027. Its primary outcomes are adverse events. No results are posted, and the registry record is internally inconsistent about blinding: the official title says double-blind while the structured field records only participants as masked.
Identity of the product itself
The substance sold under this name is not consistently one thing. An analysis of products bought online found their content was not systematically consistent with their stated descriptions. FDA records that it has encountered multiple salts and derivatives with different active moieties under the same common name, that the single nomination it received contradicted itself about which substance was being nominated, and that several suppliers' websites use the registry number of the free base for the acetate, which is a different bulk drug substance with a different molecular weight.
FDA records that TB-500 is a common name and not a United States Adopted Name, and that naming conventions used for it do not follow established chemical nomenclature standards.
What the research shows
Each statement below is labelled with the strongest kind of study supporting it, and links to that study.
- Animal researchSupportive / Low confidence
In 32 male Sprague-Dawley rats whose Achilles tendon was cut and repaired, TB-500 given for four weeks raised maximum load to failure and lowered histopathology scores compared with untreated controls.
Eight rats per group were treated intraperitoneally for four weeks after surgery. Maximum load to failure reached significance in the TB-500 group, total Bonar scores were lower at p=0.016 and total Movin scores at p=0.017. The authors call the study exploratory.
Observed in animals. Animal results frequently fail to replicate in humans.
- Male Sprague-Dawley rats, not humans.
- Eight animals per group, and the authors describe the study as exploratory and preliminary.
- A surgically cut and repaired tendon is not the overuse injury most readers have.
- The abstract does not state whether the TB-500 used was the acetylated form that is actually sold.
- Animal researchNo effect found / Low confidence
Combining TB-500 with BPC-157 produced no additional benefit over either peptide given alone in the same rat experiment.
The study included a combined group alongside each single agent. The authors report that the combination conferred no additional benefit, and suggest the two may converge on shared pathways, which they state requires confirmation.
Observed in animals. Animal results frequently fail to replicate in humans.
- One experiment, eight rats in the combined group.
- A null result in rats says nothing about what would happen in a person.
- This is the only direct test of the two together that was found.
- Animal researchSupportive / Low confidence
The unacetylated seven-amino-acid sequence promoted dermal wound repair in aged mice to an extent comparable with the full thymosin beta-4 protein.
In 26-month-old mice, where healing is delayed, the actin-binding domain reproduced as a seven-amino-acid peptide promoted repair comparably to the parent protein. This peptide lacks the acetyl group that defines TB-500.
Observed in animals. Animal results frequently fail to replicate in humans.
- Aged mice, not humans.
- The peptide tested was unacetylated, so it is not the substance sold as TB-500.
- FDA states that the profile of the unacetylated heptapeptide cannot be directly extrapolated to the acetylated form.
- The specific measures of keratinocyte migration, contracture and collagen deposition are reported for the full protein, not for the heptapeptide.
- Animal researchSupportive / Moderate confidence
After subcutaneous injection in thoroughbred geldings, TB-500 reached a plasma peak between 60 and 120 minutes and was no longer quantifiable between 6 and 10 hours.
In horses given 10 mg under the skin, plasma concentrations peaked at 0.05 and 0.08 nanograms per millilitre, then fell below the limit of quantification within 6 to 10 hours. No intravenous arm was run, so absolute bioavailability could not be established.
Observed in animals. Animal results frequently fail to replicate in humans.
- Horses, not humans.
- Without an intravenous comparison, what fraction of the dose reached the circulation is unknown.
- No equivalent measurement exists in a person by any route.
- Animal researchSupportive / Moderate confidence
TB-500 is broken down into shorter peptides, with the pattern of metabolites characterised in horses and in rats.
Work done for anti-doping detection identified the acetylated peptide and its truncated metabolites in equine urine and plasma, and later work quantified them in rats. Ac-LK was the metabolite present at the highest concentration in rats over the first 6 hours, while Ac-LKK was still detectable at 72 hours.
Observed in animals. Animal results frequently fail to replicate in humans.
- Horses and rats.
- Metabolite identification describes what the body does to the compound, not what the compound does to the body.
- In-vitroNo effect found / Low confidence
The acetylated peptide, which is what TB-500 products contain, did not close scratch wounds in cultured fibroblasts, while one of its breakdown products did.
Confluent fibroblasts with scratch wounds were incubated for 8 hours with TB-500 at 50 micrograms per millilitre or vehicle. Wound closure did not differ from vehicle. In the same line of work the metabolite Ac-LKKTE was the fragment that showed wound healing activity.
Observed in cells or tissue outside a living organism.
- Cells in a dish, over 8 hours.
- One concentration in one assay, so this is not a demonstration that the compound is inert.
- The authors suggest the wound healing activity reported for TB-500 may belong to a metabolite rather than to TB-500 itself.
- In-vitroSupportive / Moderate confidence
The 17 to 23 fragment inhibited the proliferation and migration of cultured human hepatic stellate cells stimulated with PDGF-BB.
In a liver fibrosis model using cultured human cells, the fragment blocked the growth-factor-driven rise in PDGF beta receptor, alpha smooth muscle actin and collagen 1, and the authors report that it also blunted Akt phosphorylation with the result that proliferation and migration were inhibited. The amino-terminal fragment tested alongside it had no such effect. The direction is the opposite of the cell-migration story usually told about this sequence.
Observed in cells or tissue outside a living organism.
- Cultured human cells, not a living person.
- Hepatic stellate cells are not tendon, muscle or ligament tissue.
- The peptide used was the unacetylated fragment.
- Mechanistic reasoningSupportive / Moderate confidence
The sequence LKKTETQ contains the six-residue actin-binding motif of thymosin beta-4 and is the region associated with angiogenesis, wound healing and cell migration.
Thymosin beta-4 has several active sites with different functions. The segment LKKTET, inside the seven-residue sequence that TB-500 reproduces, is the part known to bind actin, and that region is the one linked to new vessel formation and cell movement. This is a mechanism, not an outcome.
A plausible biological explanation, not a measured outcome.
- A mechanism attributed to a sequence is not evidence that a product containing it works.
- The same review attributes different functions to other regions of the protein.
- FDA states that whether actin binding is what gives the heptapeptide its reported effects on angiogenesis and wound healing remains to be determined.
Reported and theoretical risks
- Mechanismunknown
The safety record is empty rather than reassuring
FDA searched its adverse event reporting system through 26 March 2025 and retrieved no reports for TB-500, and its literature search identified no published cases. A separate search of the food and supplement complaint system, covering 2004 to March 2025, returned two cases concerning a blend of TB-500 and BPC-157, and those reports carried no safety assessment. FDA states it has identified no clinical study or human exposure data by any route, and that the potential risks in people are therefore unknown. An empty database measures the absence of observation rather than the absence of harm.
- Mechanismunknown
No toxicology study of any kind has been conducted, in any species
FDA reports finding no acute toxicity study, no repeat-dose study, no genotoxicity study, no developmental or reproductive study and no carcinogenicity study for either TB-500 free base or TB-500 acetate. There is no dose at which anything is known to be safe in any animal.
- Mechanismtheoretical
Immunogenicity has never been studied
The routes by which this compound is used are injected ones, which carry more immunogenic risk than oral or topical administration, and peptide aggregation and impurities add to it. No study investigating the question was identified, so this is reasoning from peptide chemistry rather than an observed harm.
- Mechanismtheoretical
A sequence associated with new blood vessel formation raises an untested question about tumour growth
The region of thymosin beta-4 that TB-500 reproduces is linked to angiogenesis and cell migration, and solid tumours depend on new vessels. No study in any species has tested whether TB-500 affects tumour growth or incidence, so this is an inference from a mechanism and not a reported harm.
- Mechanismmoderate
Products sold under this name do not reliably contain what they claim
An analysis of products bought online found that the content of TB500 and TB1000 products is not systematically consistent with their stated descriptions. FDA separately records that one common name covers different active moieties, and that suppliers reuse the free base registry number for the acetate, which is a different substance.
Regulatory status
Status differs by country and changes over time. Each entry is dated and sourced.
USFDAnot approved
Never approved. There is no United States Pharmacopeia or National Formulary monograph for either TB-500 free base or TB-500 acetate, and neither is a component of an approved drug. In 2026 FDA evaluated both for the 503A Bulk Drug Substances List, for wound healing, after the single nomination was withdrawn and FDA continued at its own discretion. It proposed not adding either. The matter went to the Pharmacy Compounding Advisory Committee on 23 July 2026 and no vote or final determination is published, so this is a proposal rather than a decision.
As of 15 May 2026. Source
EUEMAnot approved
No product containing TB-500 has been authorised for use in the European Union, and the substance is not recognised in the European Pharmacopoeia. This rests on FDA's account rather than on an EMA document, because nothing could be retrieved from EMA directly, so it is recorded here at second hand and needs confirmation against EMA.
As of 15 May 2026. Source
internationalWADAbanned in sport
Named in section S2.3, growth factors and growth factor modulators, as a derivative of thymosin beta-4, and prohibited at all times. Substances in that section are non-Specified Substances, a stricter classification than the Specified Substances of section S0 where BPC-157 sits, which matters for how a positive test is handled. The section number, the section title and the non-Specified classification were read from WADA's published list on 2 October 2026. FDA's briefing document independently records the S2.3 listing, but not the section title and not the classification.
As of 2 October 2026. Source
Research and analysis
Related peptides
- BPC-157A 15-amino-acid fragment of a gastric juice protein, studied mostly in rats for tendon and muscle healing
Sources
- 1. Biçer O et al. Effects of BPC-157 and TB-500 on Achilles tendon healing in rats: A histopathological and biomechanical study. Joint Diseases and Related Surgery. 2026. PubMed 42542926
- 2. Rahaman KA et al. 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. Journal of Chromatography B, Analytical Technologies in the Biomedical and Life Sciences. 2024. PubMed 38382158
- 3. FDA Briefing Document, Pharmacy Compounding Advisory Committee Meeting, July 23-24, 2026: Evaluation of TB-500-related Bulk Drug Substances (TB-500 (Free Base) and TB-500 acetate) for Inclusion on the 503A Bulk Drug Substances List. U.S. Food and Drug Administration. 2026. View source(open access)
- 4. Philp D et al. Thymosin beta 4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged mice. Wound Repair and Regeneration. 2003. PubMed 12581423
- 5. Sosne G et al. Biological activities of thymosin beta4 defined by active sites in short peptide sequences. FASEB Journal. 2010. PubMed 20179146
- 6. Ho ENM 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. PubMed 23084823
- 7. Shah R, Reyes-Gordillo K, Rojkind M. Thymosin beta 4 inhibits PDGF-BB induced activation, proliferation, and migration of human hepatic stellate cells via its actin-binding domain. Expert Opinion on Biological Therapy. 2018. PubMed 30063851
- 8. Delcourt V et al. TB500/TB1000 and SGF1000: A scientific approach for a better understanding of misbranded and adulterated drugs. Drug Testing and Analysis. 2023. PubMed 36482504
- 9. The Prohibited List, World Anti-Doping Agency. World Anti-Doping Agency. 2026. View source(open access)