# TB-500: full monograph (TB-500 Co)
> Source page: https://tb500co.com/monograph

Status: Research compound, not FDA-approved
Disclosure: TB-500 (a thymosin beta-4 fragment) is not FDA approved. FDA reports no human exposure data for it, and it is sold only for research use with no established human efficacy.
Updated: 2026-08-14

## Key facts
- Status: Research compound, not FDA-approved
- Human PK of the fragment: None published (source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks)
- Human half-life of the fragment: Never measured (source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks)
- Human bioavailability of the fragment: Never measured by any route (source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks)
- Rat metabolism: Ac-LK primary metabolite at 0-6 h; Ac-LKK detectable to 72 h (source: https://europepmc.org/article/MED/38382158)
- Active moiety in question: Only the metabolite Ac-LKKTE showed significant wound-repair activity, not the parent peptide (source: https://europepmc.org/article/MED/38382158)
- Equine detection: Parent and Ac-LK confirmed in plasma and urine after a single 10 mg subcutaneous dose; limits about 0.01 to 0.02 ng/mL (source: https://europepmc.org/article/MED/23084823)
- Surface adsorption: TB-500 is a published model peptide for loss to glassware and plasticware; stated concentration is not always delivered concentration (source: https://europepmc.org/article/MED/28887173)
- Human PK of the full protein (different molecule): Dose-proportional exposure with half-life increasing with dose, at 42 to 1260 mg IV (source: https://europepmc.org/article/MED/20536472)
- Class: Synthetic 7-amino-acid peptide; the acetylated actin-binding fragment (residues 17-23) of thymosin beta-4 (source: https://pubchem.ncbi.nlm.nih.gov/compound/62707662)
- Sequence: Ac-LKKTETQ (Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln) (source: https://pubchem.ncbi.nlm.nih.gov/compound/62707662)
- Molecular weight: 889.0 Da (C38H68N10O14), CAS 885340-08-9 (source: https://pubchem.ncbi.nlm.nih.gov/compound/62707662)
- Parent protein: Thymosin beta-4: 43 amino acids, 4963 Da. A different molecule, about 5.6 times the mass (source: https://pubchem.ncbi.nlm.nih.gov/compound/45382195)
- FDA human exposure data: None identified by FDA for the fragment (source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks)
- July 2026 PCAC: FDA proposed that TB-500 free base and TB-500 acetate NOT be added to the 503A compounding list (source: https://www.fda.gov/media/193342/download)
- WADA 2026: Named under S2.3 as thymosin beta-4 and its derivatives; prohibited at all times; non-Specified Substance (source: https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf)
- Published human studies of the fragment: 0. One phase 1/2 safety study is recruiting with no results posted (source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks)
- Participants in registered trials of the full protein: 2,143 across 15 completed or terminated trials (source: https://clinicaltrials.gov/study/NCT02597803)
- Human pharmacokinetics of the fragment: None published; no half-life, bioavailability or clearance measured in a person (source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks)
- Animal metabolism: In rats, Ac-LK dominates at 0-6 h; Ac-LKK detectable to 72 h; only the metabolite Ac-LKKTE showed wound-repair activity (source: https://europepmc.org/article/MED/38382158)
- Best-documented in vivo dose: 10 mg subcutaneously, in horses, administered by racing laboratories to build detection tests (source: https://europepmc.org/article/MED/23084823)
- Established human dose: None. No human dose-finding study has been published (source: https://clinicaltrials.gov/study/NCT07487363)
- Product content: Analysis of marketed TB500 and TB1000 found content not systematically consistent with its descriptions (source: https://europepmc.org/article/MED/36482504)

## What is TB-500?
TB-500 is a synthetic 7-amino-acid peptide: the sequence Leu-Lys-Lys-Thr-Glu-Thr-Gln with an acetyl group on the front end, written Ac-LKKTETQ, molecular weight 889 Da 34 . That sequence is residues 17 to 23 of a much larger natural protein called thymosin beta-4, which is 43 amino acids and 4963 Da 35 . Residues 17 to 23 are the part of the protein that binds actin, which is why a fragment was cut out and sold in the first place 6 . When doping-control chemists bought a TB-500 product and put it through high-resolution mass spectrometry in 2012, what they found in the vial was exactly that: the N-terminally acetylated 17-23 fragment of human thymosin beta-4 1 . FDA lists the same substance on its compounding safety-risks page under the name "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" 30 . This distinction is the whole story of this site, and it is the reason the page exists. The impressive human trial record that appears in TB-500 marketing belongs to the full 43-amino-acid protein, not to the fragment in the vial. This monograph labels every study row with the molecule that was actually administered, alongside the species, so you can see which is which without taking anyone's word for it.
Sources: https://pubchem.ncbi.nlm.nih.gov/compound/62707662 ; https://europepmc.org/article/MED/22962027 ; https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks

## Key facts at a glance
Every chip below carries an evidence grade and, where a study is involved, the molecule that was actually tested. Animal means rat, mouse or horse data; in vitro means cell or tissue experiments; regulatory means an FDA, WADA or registry record. None of these facts rests on a completed human trial of the fragment, because none exists.

## Is TB-500 the same thing as thymosin beta-4?
No, and the gap is not a technicality. Thymosin beta-4 is a 43-amino-acid protein of 4963 Da 35 . TB-500 is a 7-amino-acid fragment of 889 Da with an acetyl cap that the natural protein does not have 34 1 . One is roughly a sixth of the mass of the other and carries a chemical modification that does not occur in the body. The consequence is what matters. Thymosin beta-4, the full protein, has a real clinical trial history: eye drops (RGN-259) taken through phase 3 in dry eye and neurotrophic keratopathy, topical gels (RGN-137) taken through phase 2 in venous stasis ulcers, pressure ulcers and epidermolysis bullosa, and recombinant human thymosin beta-4 taken through phase 1 and phase 2 in China. Adding up actual enrolment across the 15 completed or terminated registered trials of the full protein listed below gives 2,143 participants. The number of people who have completed a registered trial of the LKKTETQ fragment sold as TB-500 is zero. There is now one registry record for the fragment itself: a phase 1/2 randomized, placebo-controlled dose-escalation study in adults with stable atherosclerotic cardiovascular disease, target 80 participants, sponsored by Hudson Biotech, first posted in March 2026, with treatment-emergent and serious adverse events as its primary endpoints. It is recruiting in Shenzhen and has posted no results 37 . A recruiting safety study is not evidence of benefit; it is the field admitting the safety question is still open. So when a vendor page cites "clinical trials" for TB-500, the honest reading is almost always: those trials tested a different molecule, usually by a different route, often into an eye or onto a wound rather than into a muscle. The table below is the full-protein trial ledger, published so the 2,143 figure can be recomputed by anyone who wants to add it up.
Sources: https://clinicaltrials.gov/study/NCT07487363 ; https://pubchem.ncbi.nlm.nih.gov/compound/45382195

## Regulatory status: FDA, compounding, and sport
TB-500 (a thymosin beta-4 fragment) is not FDA approved. FDA reports no human exposure data for it, and it is sold only for research use with no established human efficacy. A Drugs@FDA search returns no approved product containing thymosin beta-4 in any form 33 . FDA has said more than that. Its compounding safety-risks list carries an entry headed "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500", which states that compounded drugs containing the fragment "may pose risk for immunogenicity for certain routes of administration due to the potential for aggregation as well as peptide-related impurities", that "FDA has not identified any human exposure data" for drug products containing it, and that the agency "lacks important information regarding any safety issues raised by this drug, including whether it would cause harm if administered to humans" 30 . That page was current as of April 22, 2026. On July 23, 2026, FDA's Pharmacy Compounding Advisory Committee took up TB-500-related bulk drug substances 31 . The nomination (from Wells Pharmacy Network) had been withdrawn by the nominator, but FDA elected to proceed with the presentation anyway, and its briefing document states plainly: "FDA is proposing that TB-500 (free base) NOT be included on the 503A Bulks List" and "FDA is proposing that TB-500 acetate NOT be included on the 503A Bulks List" 32 . Committee advice is non-binding and rulemaking is pending. Being added to that list would not make a substance FDA approved in any case; it would only make it legal for pharmacies to compound. In sport, the 2026 WADA Prohibited List names "Thymosin-beta4 and its derivatives e.g. TB-500" under section S2.3, growth factors and growth factor modulators 36 . S2 is prohibited at all times, in and out of competition, and the list states that all prohibited substances in the S2 class are non-Specified Substances. That last detail matters and is often missed: our sister site covers BPC-157, which sits in S0 where every substance is a Specified Substance. TB-500 sits in S2, where they are not. Specified status is what gives an athlete room to argue that a substance was more likely taken for a reason other than performance; TB-500 does not have it.
Sources: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks ; https://www.fda.gov/media/193342/download ; https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf

## Proposed mechanisms (all preclinical)
The mechanistic case for the fragment is a structural argument, not a clinical one. Thymosin beta-4 is the major actin-sequestering molecule in eukaryotic cells, and its actin-binding site is the LKKTETQ sequence at residues 17 to 23. A 2010 review by the group that mapped these sites reports that a short sequence containing LKKTETQ promotes angiogenesis, wound repair and cell migration, while a different fragment at the other end of the protein (Ac-SDKP) blocks inflammation and reduces fibrosis 6 . Different fragments, different jobs, and neither one is the whole protein. Direct fragment work exists and is worth reading precisely. In human hepatic stellate cells, the 17-23 peptide but not the 1-15 peptide blocked PDGF-BB-driven upregulation of the PDGF receptor, alpha-SMA and collagen 1, and inhibited proliferation and migration; the authors concluded the anti-fibrogenic action of thymosin beta-4 is exerted via 17-23 7 . In wounded skin, the LKKTETQ peptide significantly enhanced repair in vitro and in vivo, with the effect suggested to run through purinergic receptors 5 . The full protein's mechanism literature is broader and better known, which is exactly why it gets borrowed. Thymosin beta-4 forms a complex with PINCH and integrin-linked kinase, activates Akt, and improved early myocyte survival and cardiac function after coronary artery ligation in mice 16 . That is a mouse result about a 43-amino-acid protein. It is not a TB-500 result. One 2024 finding complicates the fragment story from the inside. When TB-500 was given to rats and its metabolites profiled, the parent peptide was not the most active thing present: only the metabolite Ac-LKKTE showed significant wound-repair activity in the fibroblast assay, and the authors wrote that "the previously reported wound-repair activity of TB-500 in literature may be due to its metabolite Ac-LKKTE rather than the parent form" 2 . Nobody has resolved that.
Sources: https://europepmc.org/article/MED/20179146 ; https://pmc.ncbi.nlm.nih.gov/articles/PMC6748868/ ; https://europepmc.org/article/MED/38382158

## What the research shows, by species and by molecule
The table below is the core of this monograph: 26 primary research and registry entries, each labelled with the species, the route, and the molecule that was actually administered. The species census is 14 human rows and 12 nonhuman or laboratory rows. The molecule census is what makes this compound unusual: 11 rows tested the TB-500 fragment, 13 tested the full 43-amino-acid protein, 1 tested both side by side, and 1 human row records a peptide the source calls "TB4" without saying which molecule it was. Cross that census with the species column and the honest summary falls out. Of the 11 fragment rows, 10 are animal, in vitro or analytical, and the single human one is a registry record with no results 37 . Of the 13 full-protein rows, 12 are human. The human evidence and the fragment do not overlap anywhere in this table. Independent reviewers describe the field the same way. A 2026 scoping review in the American Journal of Sports Medicine covering six popular peptides including TB-500 found that 67% of identified publications used preclinical animal models, that human clinical studies were "limited to a handful of investigations, most lacking robust controls or rigorous study designs", and concluded that the claimed benefits "remain unsubstantiated by current human trials" 25 . A 2026 narrative review in Sports Medicine covering the same gray market notes that many unapproved peptides show favourable outcomes in animal models "but rigorous human safety data are scarce, and there is potential for serious harm" 26 . A 2026 primer for orthopaedic surgeons states that thymosin beta-4 and its derivative TB-500 "promoted angiogenesis and tissue repair in preclinical models, but human orthopaedic data are lacking, and both remain banned substances in sports" 27 . A 2026 review of therapeutic peptides in orthopaedics lists TB-500 among the wound-repair peptides and states plainly that despite promising preclinical studies "there is a current lack of clinical trials" 28 .
Sources: https://europepmc.org/article/MED/42578445 ; https://europepmc.org/article/MED/41966639 ; https://europepmc.org/article/MED/41476424

## What has actually been tested on the fragment
Strip away everything that tested the full protein and this is what is left for the molecule in the vial. One rat tendon study, from 2026. An independent Turkish orthopaedic group transected and repaired the Achilles tendon in 32 rats and randomised them to control, BPC-157 at 10 ug/kg/day, TB-500 at 60 ug/kg/day, or both, given intraperitoneally for four weeks. Maximum load to failure was higher in both peptide groups than in controls, reaching statistical significance in the TB-500 group (p < 0.05). Total Bonar scores were significantly lower with TB-500 (p = 0.016) and total Movin scores were significantly lower with TB-500 and with the combination (p = 0.017 and p = 0.040). BPC-157 alone was numerically better without reaching significance on total scores, and the combination added nothing over either agent alone 3 . We report that result at the grade it actually holds, and the grade is low. This is one exploratory study, 8 rats per group, four weeks, in an animal whose Achilles tendon is not a human one, published by authors who themselves describe the findings as preliminary and call for dose optimisation and longer-term work. Our sister site on BPC-157 presented the same study against its own compound's interest, and we are not going to spend it as a marketing point here just because the arrow points our way this time. A single rat study is a single rat study in both directions. Fragment wound-repair work in mice and cells. The 7-amino-acid peptide promoted repair in 26-month-old aged mice comparably to the parent molecule in a 2003 study that tested both 4 , and LKKTETQ significantly enhanced skin wound repair in vitro and in vivo in 2006 5 . A 2025 paper built TB500 into an enzyme-triggered hydrogel and reported accelerated epithelial regeneration in an alkali burn model plus migration and proliferation of human corneal epithelial cells, calling it the first ocular application of TB500; the abstract does not state the animal species 8 . A 2026 study reported that TB500 and Ac-SDKP improved Morris water maze and novel object recognition performance in 5xFAD mice while leaving hippocampal amyloid burden unchanged 9 . Metabolism, in rats. After TB-500 was administered to rats, Ac-LK was the primary metabolite in the 0 to 6 hour window and Ac-LKK was detectable to 72 hours; no cytotoxicity was found for parent or metabolites; and only Ac-LKKTE showed significant wound-repair activity in the assay 2 . That is the complete fragment efficacy literature relevant to what people buy TB-500 for: one rat tendon study, a handful of mouse and cell wound experiments, one hydrogel formulation study, and one rat metabolism study that questions whether the parent peptide is the active molecule at all. There is no human efficacy study of any kind.
Sources: https://europepmc.org/article/MED/42542926 ; https://europepmc.org/article/MED/12581423 ; https://europepmc.org/article/MED/41359360

## What the full-protein human trials actually found
Because the full protein's trials get cited on TB-500 pages, it is worth reporting what they found, in full, including the parts that do not flatter the molecule. Dry eye. A phase 2 trial randomised 72 subjects to 0.1% thymosin beta-4 eye drops or placebo in a controlled adverse environment model. Neither primary endpoint, ocular discomfort or inferior corneal staining, showed a significant difference. Several secondary endpoints did: discomfort during the environmental challenge was reduced 27% (P = 0.0244), and central and superior corneal staining improved (P = 0.0075 and P = 0.0210) 17 . A separate 9-patient phase 2 trial in severe dry eye reported 35.1% less ocular discomfort and 59.1% less total corneal fluorescein staining versus vehicle at day 56 18 . The program then went to phase 3 three times: ARISE-1 (317 participants), ARISE-2 (601) and ARISE-3 (700) 40 39 38 . In the results posted for ARISE-2, mean change from baseline at day 29 was 0.07 for RGN-259 versus -0.04 for placebo on ocular discomfort, and 0.07 versus -0.01 on corneal fluorescein staining: neither co-primary endpoint favoured the drug 39 . Neurotrophic keratopathy. The phase 3 SEER-1 trial was terminated after 18 participants for a business decision 41 . The 2025 Cochrane review of interventions for neurotrophic keratopathy included it and found that 0.1% RGN-259 may not increase the proportion of participants achieving corneal re-epithelialization (RR 9.00, 95% CI 0.57 to 141.88; 18 participants; low-certainty evidence) 23 . A confidence interval running from 0.57 to 141.88 is a statement that nobody knows. SEER-2 is recruiting 42 . Chronic wounds. Phase 2 trials of topical thymosin beta-4 gel ran in venous stasis ulcers and pressure ulcers, 72 participants each, both with results posted 46 47 . The venous ulcer study, run at eight European sites and randomising 73 patients, reported that the safety profile at all doses was acceptable and comparable to placebo, and that efficacy findings "suggest that a Tbeta4 dose of 0.03% may have potential to speed wound closure, with complete closure within three months in about 25% of patients 21 . A 2012 review by the investigators summarised both trials as shortening time to closure by almost a month in those patients whose ulcers closed 20 . Both epidermolysis bullosa trials were terminated early, one for lack of patient availability and expired study drug, the other after four participants for a business decision 48 49 . Systemic dosing. Intravenous thymosin beta-4 has been given to healthy volunteers: a published phase 1 study dosed four cohorts of 10 subjects at 42, 140, 420 or 1260 mg, single dose and then daily for 14 days, and reported infrequent mild-to-moderate adverse events with no dose-limiting toxicity 19 . Recombinant human thymosin beta-4 has since been through phase 1a (54 subjects, single IV doses of 0.5 to 25 ug/kg) and phase 1b (30 subjects, 0.5 to 5.0 ug/kg daily for 10 days) in Chinese healthy volunteers, and phase 2a and 2b trials in acute myocardial infarction with 62 and 90 participants 50 51 52 53 . None of those four records has posted results. The one US injectable program, RGN-352 for ST-elevation myocardial infarction, was withdrawn with the note "Trial never initiated", and a companion phase 1 intravenous study was withdrawn as "never initiated due to contract manufacturing issues" 54 55 . The summary for the molecule that does have trials: no regulator has approved it. A 2025 paper from an independent ophthalmology group describes RGN-259 as having reached clinical trials "with full US Food and Drug Administration approval still pending" 24 , and Drugs@FDA returns nothing for thymosin beta-4 in any form 33 . Borrowing this record for the fragment therefore borrows a record that has not itself produced an approved product.
Sources: https://pmc.ncbi.nlm.nih.gov/articles/PMC4445951/ ; https://clinicaltrials.gov/study/NCT02974907 ; https://pmc.ncbi.nlm.nih.gov/articles/PMC12679690/ ; https://europepmc.org/article/MED/20536472

## The horse-racing record
The best-documented in vivo administrations of TB-500 in the published literature are not in humans or rodents. They are in horses, and they were done by racing laboratories trying to catch it. In 2012 the Hong Kong Jockey Club racing laboratory published a detection method for TB-500 in equine urine and plasma, describing it as "a veterinary preparation known as TB-500 and containing a synthetic version of the naturally occurring peptide LKKTETQ". The method confirmed the parent peptide at 0.02 ng/mL in plasma and 0.01 ng/mL in urine, and was validated on samples from horses given a single dose of TB-500 containing 10 mg of N-acetylated LKKTETQ. The authors describe it as the first identification of TB-500 and its metabolites in post-administration samples from horses 10 . A companion 2013 paper extended the method to seven peptides and reported detection of N-acetylated LKKTETQ and its metabolite after subcutaneous administration of TB-500 (10 mg) to two thoroughbred geldings 11 . The French racing laboratory published a 2025 population study establishing baseline endogenous thymosin beta-4 concentrations in racing horses, noting that its use is "forbidden by the IFHA, the FEI, and the WADA" while "numerous products available online" claim to contain either a synthetic acetylated fragment of the protein or the protein itself. They also showed that a non-natural synthesis impurity is detectable in equine plasma after a single administration of a TB4-containing product 12 . Two things follow. First, the dose scale that has actually been administered and measured in a large mammal is 10 mg subcutaneously, in a horse, for the purpose of building a test. Second, an impurity signature specific to synthesis is one of the ways these products are identified, which tells you something about what is in them. We looked for individual racing-authority disciplinary actions naming TB-500 and did not verify any against a primary regulator source within this build, so none is cited here. The peer-reviewed racing-laboratory literature above is the documentable part of the horse-doping story, and it is enough.
Sources: https://europepmc.org/article/MED/23084823 ; https://europepmc.org/article/MED/23318763 ; https://europepmc.org/article/MED/39314109

## Human evidence: what exists and what does not
No human study of the LKKTETQ fragment has ever been published, for any indication, of any design. FDA's own position, stated on its compounding safety-risks page, is that it "has not identified any human exposure data" for drug products containing the thymosin beta-4 fragment 30 . That is a regulator saying it could not find evidence that people have taken this and been followed. Two things sit adjacent to that emptiness and get mistaken for filling it. The first is the registry record: the phase 1/2 dose-escalation safety study in stable atherosclerotic cardiovascular disease, 80 participants planned, three sequential dose cohorts randomised 3:1 against placebo, primary endpoints treatment-emergent and serious adverse events, recruiting since February 2026, no results posted 37 . When it reports, it will be the first human safety data on this molecule. Until then it is a plan, not a finding. The second is a retrospective knee-pain chart review from a Florida clinic, which is the only published human report anywhere that involves a peptide the authors call TB4. Of 16 patients reached by telephone, 12 had received BPC-157 alone and 4 had received BPC-157 combined with TB4; of those 4, three reported significant improvement and one reported no relief. There was no control group, no imaging, and "no specific tools were used to measure their improvement" 29 . The abstract names "thymosin-beta-4 (TB4)" and never states whether the injected material was the full protein or the fragment, so it cannot be attributed to TB-500 at all. Four uncontrolled patients on a combination of two peptides, with the molecule unidentified, is not a basis for anything. Everything else offered as human evidence for TB-500 is evidence about thymosin beta-4, the full protein, and belongs to the section above.
Sources: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks ; https://clinicaltrials.gov/study/NCT07487363 ; https://europepmc.org/article/MED/34324435

## Pharmacokinetics: absent in humans, thin in animals
There is no human pharmacokinetic study of TB-500. No half-life, no bioavailability, no exposure curve, no clearance route has been measured in a person for this molecule, which follows directly from FDA having identified no human exposure data at all 30 . What exists is animal and analytical. In rats given TB-500, Ac-LK was the metabolite present at highest concentration in the 0 to 6 hour interval and Ac-LKK persisted as a long-term metabolite detectable to 72 hours 2 . In horses, the parent peptide and the Ac-LK metabolite were confirmed in plasma and urine after a single subcutaneous 10 mg dose, at detection limits around 0.01 to 0.02 ng/mL 10 11 . Separate rat work on the full protein identified Ac-Tb1-14 as a urinary metabolite quantifiable to 48 hours after a 20 mg/kg intraperitoneal dose, with peak concentrations between 0 and 6 hours 14 . A practical laboratory note that also matters for anyone handling this compound: TB-500 is one of four model peptides used in a published study of adsorption to glassware and plasticware, precisely because peptides at low concentration stick to surfaces and disappear from solution 15 . Concentration in a vial is not a fixed property of the vial. By contrast, the full protein does have published human pharmacokinetics: single intravenous doses of 42 to 1260 mg in healthy volunteers showed a dose-proportional response and a half-life that increased with dose 19 . Those doses are between roughly 4 and 140 times the entire contents of a typical gray-market TB-500 vial, of a molecule six times larger. The two are not interchangeable in any direction.
Sources: https://europepmc.org/article/MED/38382158 ; https://europepmc.org/article/MED/20536472

## Forms and routes: what is sold versus what was studied
TB-500 is sold as a lyophilised powder in sealed vials, commonly labelled 2 mg, 5 mg or 10 mg, to be reconstituted with bacteriostatic water and injected. FDA's compounding entry addresses exactly this class of product and flags immunogenicity risk "for certain routes of administration" 30 . The research routes are a different map. The fragment's animal efficacy work used intraperitoneal injection (the rat tendon study, 60 ug/kg/day) 3 , topical application (the mouse wound studies) 4 5 , and an ocular hydrogel 8 . The documented large-animal route is subcutaneous, in horses, at 10 mg 10 . The full protein's human work is overwhelmingly topical or ocular: eye drops in every dry eye and keratopathy trial, gel in every wound trial. The only systemic human route studied is intravenous, and only for the full protein 19 . Nobody has published a study of subcutaneous or intramuscular TB-500 in a human being. That is the route almost everyone buying it uses. See the fragment-versus-full-protein comparison table for the route-by-route breakdown.
Sources: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks ; https://europepmc.org/article/MED/42542926

## What doses have been used in research?
There is no established human dose of TB-500. No human dose-finding study has been published, and the one registered dose-escalation study has not reported its dose levels publicly or posted any results 37 . The doses that do exist, labelled by molecule and species: the fragment was given at 60 ug/kg/day intraperitoneally for four weeks to rats in the 2026 tendon study 3 , and as a single subcutaneous dose containing 10 mg of N-acetylated LKKTETQ to horses in the racing-laboratory administration studies 10 11 . The full protein was given intravenously to healthy human volunteers at 42, 140, 420 and 1260 mg 19 , and recombinant human thymosin beta-4 at 0.5 to 25 ug/kg intravenously in phase 1 and 0.25 to 2.0 ug/kg in the myocardial infarction trials 50 52 . Topical human trials used concentrations, not masses: 0.01%, 0.03% and 0.1% gels and 0.1% eye drops 46 40 . Those numbers sit in four different unit systems across two different molecules and four species. There is no validated method for converting any of them into a dose for a person injecting the fragment, and this site does not attempt one. Our study-dose explorer displays every published dose with its molecule and species attached, and our reconstitution calculator does arithmetic on numbers you enter. Neither recommends a dose, because no source supports one.
Sources: https://clinicaltrials.gov/study/NCT07487363 ; https://europepmc.org/article/MED/42542926 ; https://europepmc.org/article/MED/20536472

## Is TB-500 safe?
Nobody knows, and that is not a hedge. FDA states it "lacks important information regarding any safety issues raised by this drug, including whether it would cause harm if administered to humans", having identified no human exposure data for it at all 30 . There is no human safety dataset to summarise. What is reported: in the rat metabolism study, neither the parent peptide nor its metabolites showed cytotoxicity in the assays used 2 , and no adverse effects were reported in the small animal efficacy studies. Absence of observed harm in rats and in cell assays is not human safety evidence, and no animal toxicology program for this fragment has been published. What is specifically flagged as unassessed is immunogenicity: FDA's stated concern is that compounded drugs containing the fragment "may pose risk for immunogenicity for certain routes of administration due to the potential for aggregation as well as peptide-related impurities" 30 . Aggregation is a specific property of peptides in solution, and the aggregation behaviour of this peptide in the vials being sold has not been characterised in any published work we could find. Two further considerations belong here honestly. The proposed mechanism is pro-angiogenic and pro-migratory: the same actin-binding and cell-migration biology that is offered as the benefit is biology that people with a cancer history should want a clinician's view on before going near it, and no study has examined that population 6 . And the practical risk sits upstream of pharmacology entirely: the contents of the vial. See the sourcing section.
Sources: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks ; https://europepmc.org/article/MED/38382158

## What side effects have been reported?
No side-effect profile exists for TB-500 in humans, because no human study of the fragment has reported one. Any list of TB-500 side effects circulating online is either invented, copied from the full protein, or extrapolated from other peptides. The nearest real data are for the different molecule. In the published phase 1 study of intravenous thymosin beta-4 in 40 healthy volunteers at 42 to 1260 mg, adverse events were "infrequent, and mild or moderate in intensity", with no dose-limiting toxicities and no serious adverse events 19 . In the topical wound trials the safety profile at all doses was described as acceptable and comparable to placebo 21 , and the small dry eye trials reported no adverse events 17 . Those are tolerability findings for a 43-amino-acid protein given intravenously, in an eye or onto a wound. They say nothing about a 7-amino-acid acetylated fragment injected under the skin from an unregulated vial. The registered phase 1/2 study of the fragment has treatment-emergent adverse events and serious adverse events as its two primary endpoints 37 . That is the study designed to answer this question, and it has not answered it yet.
Sources: https://europepmc.org/article/MED/20536472 ; https://clinicaltrials.gov/study/NCT07487363

## Who has never been studied?
For the fragment, the honest answer is everyone. No human population has been studied, so every group below is an absence rather than a documented risk. Groups with zero data and specific reasons for caution: pregnant or breastfeeding people; children; people with a current or past cancer, given that the proposed mechanism is pro-angiogenic and pro-migratory 6 16 ; people with cardiovascular disease, who are precisely the population the first registered human study is now enrolling under close safety monitoring 37 ; and people with immune conditions, since immunogenicity is the specific risk FDA names as unassessed 30 . No drug interaction study of TB-500 exists in any species. None of the published animal work co-administered other drugs and measured an interaction. Tested athletes are a separate case with a definite answer. Thymosin beta-4 and its derivatives including TB-500 are prohibited at all times under WADA S2, and S2 substances are non-Specified, which removes the mitigation route that Specified status can provide 36 . In horse racing the same applies through IFHA and FEI rules, with validated detection methods in routine use 12 .
Sources: https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf ; https://clinicaltrials.gov/study/NCT07487363

## What is actually in a TB-500 vial?
This is the question with the best published answer on the whole page, and the answer is not reassuring. A French racing laboratory bought products sold as TB500, TB1000 and SGF1000 over the internet and analysed them. Their conclusion: "the content of TB500/TB1000 products is not systematically consistent with it's former descriptions", and the third product, SGF1000, was mainly sheep extracellular matrix and blood proteins with the purported active ingredient "excessively diluted" 13 . Independently, the 2012 Ghent doping-control work that first characterised a TB-500 product had to synthesise Ac-LKKTETQ themselves to have a reference standard to compare against 1 , and the 2024 Korean metabolism work noted that TB-500 and its metabolites had never been simultaneously quantified or structurally identified using synthesised authentic standards until they did it 2 . Racing laboratories also report detecting non-natural synthesis impurities in equine plasma after administration of a TB4-containing product, which is a direct measurement that these products carry manufacturing residues 12 . FDA names peptide-related impurities and aggregation potential as the specific reasons compounded versions concern it 30 . There is no USP monograph for this peptide, no pharmaceutical-grade formulation, and no validated quality standard for the vials being sold. A certificate of analysis supplied by the seller of a product is a document produced by the seller. The published record shows the contents of these products have not consistently matched their labels.
Sources: https://europepmc.org/article/MED/36482504 ; https://europepmc.org/article/MED/22962027 ; https://europepmc.org/article/MED/39314109

## How should it be stored, and what is actually known about stability?
No validated storage or reconstitution standard exists for TB-500, because no pharmaceutical-grade formulation of it exists. Handling practices circulating on forums are laboratory convention, not tested product science, and this site will not present them as data. Two documented properties are worth knowing. First, adsorption: TB-500 was selected as one of four model doping-relevant peptides in a published study of peptide loss to glassware and plasticware, which found that the best choice of consumable depends on the specific peptide's physicochemical properties rather than on price 15 . Peptide solutions lose material to container surfaces, and a stated concentration is not automatically the delivered concentration. Second, degradation to metabolites is rapid in vivo: in rats, the parent peptide gave way to Ac-LK within hours, with Ac-LKK still detectable at 72 hours 2 . The comparison molecule shows what a real formulation program looks like: the recombinant human thymosin beta-4 injection under study in China is described in its registry record as a sterile solution supplied in 1.5 mg vials stored at 2 to 8 degrees Celsius, with defined dilution to a 5 mL administration volume 53 . Nothing equivalent exists for the fragment.
Sources: https://europepmc.org/article/MED/28887173 ; https://europepmc.org/article/MED/38382158

## What we do not know yet
This block renders limits_text.

## Frequently asked questions
Twelve questions, each answered in 320 characters or fewer for the answer-ready layer, with a longer answer beneath. Every answer is consistent with the graded evidence table above and names the molecule where the molecule is the point.

## References and citation manifest
Every reference below was fetched and verified against its source on 2026-08-14: PubMed records via the NCBI E-utilities API, FDA pages and the July 2026 PCAC briefing document retrieved directly from fda.gov with a browser user agent, the 2026 WADA Prohibited List PDF text-extracted from the archived file, trial records from the ClinicalTrials.gov v2 API, chemical identity from PubChem, and approval-status absence from the openFDA Drugs@FDA API. Study and document titles are reproduced verbatim. A machine-readable version of this list ships as the citation manifest for this page.

## Study results
| Study | Species/model | n | Duration | Outcome | Effect size |
| --- | --- | --- | --- | --- | --- |
| S01 (https://europepmc.org/article/MED/42542926) | rat (Achilles tendon transection and repair; control vs BPC-157 vs TB-500 vs both) | 32 (8 per group) | 4 weeks | Maximum load to failure higher in both peptide groups than controls, reaching statistical significance in the TB-500 group; total Bonar scores significantly lower with TB-500; total Movin scores significantly lower with TB-500 and with the combination; BPC-157 numerically lower without significance on total scores; combination conferred no additional benefit | TB-500 p<0.05 max load to failure; Bonar p=0.016; Movin p=0.017; combination Movin p=0.040 |
| S02 (https://europepmc.org/article/MED/38382158) | rat and in vitro (Rat administration plus human serum, enzyme systems, liver and kidney fractions; fibroblast wound-repair (scratch) and cytotoxicity assays) | not stated in the abstract | 0 to 72 hours | Ac-LK was the primary metabolite at highest concentration in rats at 0 to 6 hours; Ac-LKK was a long-term metabolite detected to 72 hours; no cytotoxicity for parent or metabolites; only Ac-LKKTE showed significant wound-repair activity versus control; the authors state the previously reported wound-repair activity of TB-500 may be due to the metabolite Ac-LKKTE rather than the parent form | Descriptive plus assay-level activity; no efficacy endpoint |
| S03 (https://europepmc.org/article/MED/12581423) | mouse and rat (Full-thickness dermal wounds in db/db diabetic mice and in 26-month-old aged mice; earlier work in normal rats) | not stated in the abstract | 8 days (diabetic arm) | Tb4 significantly increased wound contracture and collagen deposition in diabetic mice and accelerated repair in aged mice with increases in keratinocyte migration, contracture and collagen deposition; the actin-binding domain reproduced as the 7-amino-acid peptide LKKTETQ promoted repair in aged animals comparable to the parent molecule | Direction as reported; no numeric effect sizes in the abstract |
| S04 (https://europepmc.org/article/MED/17001601) | mouse and in vitro (Skin wound fluid proteomics with in vitro and in vivo wound-repair (scratch) assays) | not stated in the abstract | assay timescales | The LKKTETQ peptide, the common actin-binding domain of thymosin beta-4 and beta-10, significantly enhanced skin wound repair in vitro and in vivo; the authors suggest the effect may be mediated by purinergic receptors | Reported significant; assay-level data |
| S05 (https://pmc.ncbi.nlm.nih.gov/articles/PMC6748868/) | in vitro (human cells) (Early-passage human hepatic stellate cell cultures treated with PDGF-BB) | cell culture (no animal n) | assay timescales | The 17-23 peptide but not the 1-15 peptide blocked PDGF-BB-dependent upregulation of the PDGF-beta receptor, alpha-SMA and collagen 1, blunted Akt phosphorylation at T308 and S473, and inhibited proliferation and migration; the authors conclude the anti-fibrogenic actions of thymosin beta-4 are exerted via 17-23 | Direction as reported; Western blot and assay-level data |
| S06 (https://europepmc.org/article/MED/41359360) | in vitro (human cells) and animal (species not stated in the abstract) (Alkali burn corneal injury model plus human corneal epithelial cells and stromal fibroblasts) | not stated in the abstract | not stated in the abstract | The hydrogel promoted human corneal epithelial cell migration, proliferation and tight junction recovery in vitro; in an alkali burn model it significantly accelerated epithelial regeneration, reduced inflammation and improved corneal barrier function; the authors describe this as the first ocular application of TB500 | Direction as reported; no numeric effect sizes in the abstract |
| S07 (https://europepmc.org/article/MED/41443105) | mouse and in vitro (5xFAD transgenic Alzheimer model plus HT22 cells, primary cortical neurons and BV2 microglia) | not stated in the abstract | not stated in the abstract | Both peptides attenuated neurite atrophy and restored viability in cell models, suppressed LPS-induced nitric oxide and pro-inflammatory cytokines in microglia, and improved Morris water maze and novel object recognition performance in 5xFAD mice; axonal density in the perirhinal cortex was restored while hippocampal amyloid burden remained unchanged | Direction as reported; behavioural and immunohistochemical endpoints |
| S08 (https://europepmc.org/article/MED/23084823) | horse (Racing-laboratory detection method validated on post-administration samples from horses) | horses administered a single dose (number not stated in this abstract) | post-administration urine and plasma sampling | N-acetylated LKKTETQ was detected and confirmed at 0.02 ng/mL in equine plasma and 0.01 ng/mL in equine urine, together with its metabolites; described by the authors as the first identification of TB-500 and its metabolites in post-administration samples from horses | Analytical detection limits as stated; no efficacy endpoint |
| S09 (https://europepmc.org/article/MED/23318763) | horse (Solid-phase extraction and high-resolution mass spectrometry in horse plasma, applied to post-administration samples) | 2 thoroughbred geldings | post-administration sampling | N-acetylated LKKTETQ and its metabolite N-acetylated LK were detected in plasma after subcutaneous administration; limits of detection for all seven peptides were estimated below 50 pg/mL | Analytical; no efficacy endpoint |
| S10 (https://europepmc.org/article/MED/39314109) | horse (Population study of endogenous thymosin beta-4 in racing horse blood, plus single-dose administration) | population study (n not stated in the abstract) | post-administration sampling | First estimate of endogenous thymosin beta-4 concentration in racing horses, which did not depend significantly on gender, age or breed; concentration rises significantly and rapidly in plasma stored at 4 degrees Celsius when not separated from blood cells; a non-natural synthesis impurity was detectable in equine plasma after a single dose of a TB4-containing product | Descriptive; no efficacy endpoint |
| S11 (https://europepmc.org/article/MED/36482504) | n/a (product analysis) (Analytical characterisation of three products purchased over the internet) | 3 products | n/a | The content of TB500/TB1000 products was not systematically consistent with its former descriptions; the comparator product SGF1000 was mainly sheep extracellular matrix and blood proteins with the purported growth promoters excessively diluted | Qualitative analytical finding |
| S12 (https://europepmc.org/article/MED/22962027) | n/a (product analysis) (High-performance liquid chromatography with high-resolution Orbitrap mass spectrometry, plus independent solid-phase synthesis of the reference standard) | 1 product | n/a | The N-terminal acetylated 17-23 fragment of human thymosin beta 4 (Ac-LKKTETQ) was detected and identified in TB-500; the peptide was also synthesised independently and an analytical strategy for plasma and urine detection was proposed | Identification; no efficacy endpoint |
| S13 (https://clinicaltrials.gov/study/NCT07487363) | human (Phase 1/2 randomized, placebo-controlled, sequential dose-escalation study in adults with stable atherosclerotic cardiovascular disease) | 80 (estimated) | study period through February 2028 | Primary endpoints are incidence of treatment-emergent adverse events and incidence of serious adverse events. Status recruiting, first posted March 2026, single site in Shenzhen, sponsor Hudson Biotech. No results posted. | No results posted |
| S14 (https://clinicaltrials.gov/study/NCT02974907) | human (Multi-center, randomized, double-masked, placebo-controlled phase 3 trial (ARISE-2)) | 601 (actual) | 28 days | In the posted results, mean change from baseline at day 29 was 0.07 for RGN-259 versus -0.04 for placebo on the ocular discomfort scale, and 0.07 versus -0.01 on corneal fluorescein staining; neither co-primary endpoint favoured the drug | Co-primary endpoint differences favoured placebo numerically |
| S15 (https://clinicaltrials.gov/study/NCT03937882) | human (Multi-center, randomized, double-masked, placebo-controlled phase 3 trial (ARISE-3)) | 700 (actual) | 14 days | Completed October 2021. No results posted on the registry record. | No results posted |
| S16 (https://clinicaltrials.gov/study/NCT02597803) | human (Multi-center, randomized, double-masked, placebo-controlled phase 2/3 trial (ARISE-1)) | 317 (actual) | 28 days | Completed July 2016. No results posted on the registry record. | No results posted |
| S17 (https://pmc.ncbi.nlm.nih.gov/articles/PMC4445951/) | human (Single-center, prospective, double-masked, placebo-controlled phase 2 trial using the controlled adverse environment model) | 72 (actual) | 32-day study period | Neither primary endpoint (ocular discomfort, inferior corneal staining) differed significantly between groups at visit 5; several secondary endpoints did, with discomfort during the environmental challenge reduced 27% and improvements in central and superior corneal staining; no adverse events observed | Discomfort P=0.0244; central staining P=0.0075; superior staining P=0.0210; primaries not significant |
| S18 (https://europepmc.org/article/MED/25826322) | human (Small multicenter, randomized, double-masked, placebo-controlled 56-day phase 2 trial at 2 US sites) | 9 patients (12 treated eyes vs 6 control eyes) | 56 days including 28-day follow-up | At day 56 the treated group showed 35.1% reduction in ocular discomfort versus vehicle and 59.1% reduction in total corneal fluorescein staining; tear film break-up time and tear volume also improved; drops were safe and well tolerated | Discomfort P=0.0141; total corneal fluorescein staining P=0.0108 |
| S19 (https://clinicaltrials.gov/study/NCT02600429) | human (Phase 3 multi-center randomized double-masked placebo-controlled trial (SEER-1), terminated; subsequently included in a Cochrane review) | 18 (actual) | 4 weeks | Terminated for a business decision. In the 2025 Cochrane review of neurotrophic keratopathy interventions, the single 0.1% RGN-259 trial may not increase the proportion of participants with corneal re-epithelialization (RR 9.00, 95% CI 0.57 to 141.88; 18 participants; low-certainty evidence) | RR 9.00 (95% CI 0.57 to 141.88); low-certainty evidence |
| S20 (https://europepmc.org/article/MED/20536470) | human (Two randomized, double-blind, placebo-controlled, dose-response phase 2 trials, in venous stasis ulcers and in pressure ulcers; the venous ulcer study ran at eight European sites) | 72 (venous stasis ulcers) and 72 (pressure ulcers); the venous ulcer report describes 73 randomised | up to 84 days | Safety at all doses was described as acceptable and comparable to placebo; efficacy findings suggested that a 0.03% dose may have potential to speed wound closure, with complete closure within three months in about 25% of patients; a later review by the investigators summarised both trials as shortening time to closure by almost a month in those patients whose ulcers closed | Dose-level signal at 0.03%; about 25% of ulcers closed completely within 3 months |
| S21 (https://clinicaltrials.gov/study/NCT00311766) | human (Two randomized placebo-controlled phase 2 trials, both terminated early) | 30 (actual) and 4 (actual) | up to 84 days | The first trial was terminated for lack of patient availability and expiration of study drug; the RGN-137 CELEB trial was terminated after 4 participants for a business decision. No efficacy conclusion is supportable from either. | Not evaluable |
| S22 (https://europepmc.org/article/MED/20536472) | human (Randomized, placebo-controlled single and multiple ascending dose phase 1 study in healthy volunteers) | 40 (4 cohorts of 10) | 14 days | Adverse events were infrequent and mild or moderate; no dose-limiting toxicities and no serious adverse events; single-dose pharmacokinetics were dose-proportional with half-life increasing with dose | Dose-proportional exposure; tolerability endpoint |
| S23 (https://clinicaltrials.gov/study/NCT04555824) | human (Randomized, double-blind, placebo-controlled phase 1a single ascending dose and phase 1b multiple ascending dose studies in Chinese healthy volunteers) | 54 (phase 1a, actual) and 30 (phase 1b, actual) | 1 day or 10 days | Both completed (2018 and 2019). Stated objectives were safety, tolerability, pharmacokinetics and potential immunological reaction. No results posted on either record. | No results posted |
| S24 (https://clinicaltrials.gov/study/NCT05485818) | human (Randomized, double-blind, placebo-controlled phase 2a and phase 2b trials after percutaneous coronary intervention) | 62 (phase 2a, actual) and 90 (phase 2b, actual) | 7 days | Both listed as completed (2021 and 2023). No results posted on either record. A phase 2c trial at 10 and 20 ug/kg is registered as not yet recruiting. | No results posted |
| S25 (https://clinicaltrials.gov/study/NCT01311518) | human (Randomized placebo-controlled phase 2 trial in ST-elevation myocardial infarction, and a companion phase 1 intravenous safety and pharmacokinetics study) | 0 (both withdrawn) | n/a | Both records are withdrawn with zero participants enrolled. The phase 2 record states "Trial never initiated"; the phase 1 record states the study was "never initiated due to contract manufacturing issues". | Not evaluable |
| S26 (https://europepmc.org/article/MED/34324435) | human (Retrospective chart review with telephone follow-up at a single Florida clinic; peptide given alone or combined with BPC-157) | 4 of 16 patients reached received the combination | follow-up 6 to 12 months after injection | Of the 4 patients who received both peptides, 75% reported significant improvement and 25% reported no relief. No control group, no imaging, and no specific tools were used to measure improvement. The molecule is not identified beyond the label TB4. | Self-reported; 3 of 4 patients |

## What we do not know yet
What is unknown about TB-500 is not a gap in the evidence, it is most of the evidence, and this block is the honest core of the monograph. (1) No human study of the LKKTETQ fragment has been published for any indication, of any design; FDA states it has not identified any human exposure data for drug products containing it, and the first study designed to produce some is recruiting with no results posted. (2) The human trial record cited for TB-500 belongs to thymosin beta-4, the full 43-amino-acid protein: a molecule 5.6 times the mass, given as eye drops, wound gel or intravenous infusion, across 15 registered trials and 2,143 participants, none of which administered the fragment. (3) Even that borrowed record is unfinished: the ARISE-2 phase 3 co-primary endpoints did not favour the drug, the Cochrane assessment of the keratopathy trial returned a confidence interval from 0.57 to 141.88, the injectable program was withdrawn before dosing anyone, and no regulator has approved the protein either. (4) Human pharmacokinetics of the fragment do not exist: no half-life, no bioavailability, no clearance route, no dose-exposure relationship in a person. (5) It is not settled that the marketed peptide is even the active molecule: the one published metabolism study found that only the metabolite Ac-LKKTE showed significant wound-repair activity, and its authors wrote that previously reported activity may belong to the metabolite rather than the parent. (6) The fragment's own efficacy literature is one exploratory rat tendon study, a handful of mouse and cell wound experiments, a hydrogel formulation study and a mouse neuroinflammation study, with no independent replication of any result in a second species by a second group. (7) The contents of the vials being sold are documented as inconsistent with their descriptions, synthesis impurities are detectable after administration, and no USP monograph, pharmaceutical-grade formulation or validated quality standard exists. Everything else on this site should be read with those seven gaps in mind.

## Questions and answers
### Is TB-500 the same as thymosin beta-4?
No. Thymosin beta-4 is a 43-amino-acid protein of 4963 Da. TB-500 is a 7-amino-acid fragment of it, 889 Da, with a synthetic acetyl cap. The human trials cited for TB-500 tested the protein, not the fragment.

No, and this is the single most important fact on this site. Thymosin beta-4 is a naturally occurring 43-amino-acid protein weighing 4963 Da. TB-500 is residues 17 to 23 of that protein, seven amino acids, 889 Da, with an acetyl group on the front that the natural sequence does not have. Doping chemists confirmed by mass spectrometry that this acetylated fragment is what a TB-500 product contains, and FDA lists the substance as "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500".The consequence is that the trial record routinely quoted in TB-500 marketing belongs to the protein: eye drops through three phase 3 dry eye trials, wound gels through phase 2, intravenous dosing in healthy volunteers. Fifteen completed or terminated registered trials of the full protein enrolled 2,143 people. Completed trials of the fragment: none.

### Is TB-500 FDA approved?
No. TB-500 (a thymosin beta-4 fragment) is not FDA approved. FDA reports no human exposure data for it, and it is sold only for research use with no established human efficacy. Drugs@FDA returns no product.

No. TB-500 (a thymosin beta-4 fragment) is not FDA approved. FDA reports no human exposure data for it, and it is sold only for research use with no established human efficacy. A Drugs@FDA search returns no approved product containing thymosin beta-4 in any form.FDA has also put the substance on its compounding safety-risks list, stating that compounded drugs containing the fragment may pose immunogenicity risk from aggregation and peptide-related impurities, that it has not identified any human exposure data, and that it lacks the information needed to know whether the drug would cause harm in humans. In July 2026 FDA proposed that neither TB-500 free base nor TB-500 acetate be added to the 503A compounding list.

### What human evidence exists for TB-500?
None published, for any indication. FDA states it has not identified any human exposure data for the fragment. One phase 1/2 safety study (80 participants planned) started recruiting in 2026 and has posted no results.

None. No human study of the LKKTETQ fragment has been published for any indication, of any design, and FDA states on its compounding page that it has not identified any human exposure data for drug products containing it.Two things sit next to that gap. The first is a registry record: a phase 1/2 randomized, placebo-controlled, sequential dose-escalation study in adults with stable atherosclerotic cardiovascular disease, 80 participants planned, primary endpoints treatment-emergent and serious adverse events, recruiting since February 2026, no results posted. The second is a retrospective knee-pain chart review in which 4 of 16 patients received a peptide the authors call TB4 alongside BPC-157, with no controls and no measurement instruments, and the abstract never says which molecule it was. Neither is evidence that TB-500 does anything.

### How does TB-500 compare with BPC-157?
Both are unapproved research peptides FDA proposed against listing in July 2026. BPC-157 has 3 small human pilots; TB-500 has none. In one 2026 rat Achilles study TB-500 reached significance and BPC-157 did not. That is one rat study.

They share a regulatory position and differ in evidence shape. Both are unapproved, both are on FDA's compounding safety-risks list, and in July 2026 FDA proposed that neither be added to the 503A compounding list. In sport, BPC-157 sits in WADA S0 where substances are Specified; TB-500 sits in S2 where they are not, which is the stricter side.On evidence, BPC-157 has a large rodent literature and three small uncontrolled human pilots; TB-500 has a much smaller fragment literature and zero human studies. The two have been compared directly once: a 2026 study in 32 rats with transected Achilles tendons, in which TB-500 at 60 ug/kg/day reached statistical significance on maximum load to failure and on total Bonar and Movin scores, BPC-157 at 10 ug/kg/day did not reach significance on total scores, and the combination added nothing.We report that the same way our BPC-157 site does, which is to say carefully. Eight rats per group, four weeks, one exploratory study whose own authors call the findings preliminary. It is not a reason to choose one peptide over the other, and neither has been shown to do anything in a person.

### Should TB-500 be stacked with BPC-157?
There is no evidence for stacking. The only study that tested the combination found it "did not confer additional benefits" over either peptide alone, in rats. No human study has tested either peptide alone, let alone together.

The stack is folklore, and for once there is a data point pointing at it. The 2026 rat Achilles study included a combination arm precisely to test this, and reported that combined BPC-157 and TB-500 treatment "did not confer additional benefits compared to either agent alone", with the authors suggesting the two may converge on shared downstream pathways.That is one rat study and it cannot settle the question. What can be said flatly is that no human study has tested TB-500 alone, no human study has tested the combination, and the only published human report involving both peptides together is four patients in an uncontrolled knee-pain chart review where the molecule was never identified. Protocols circulating online that specify doses, ratios and cycle lengths for a stack are not derived from any published source.

### Is TB-500 banned in sport?
Yes, at all times. The 2026 WADA Prohibited List names "Thymosin-beta4 and its derivatives e.g. TB-500" under S2.3, and states that all S2 substances are non-Specified Substances. Horse racing bans it too.

Yes, in and out of competition. The 2026 WADA Prohibited List names "Thymosin-beta4 and its derivatives e.g. TB-500" in section S2.3, growth factors and growth factor modulators. S2 is prohibited at all times, and the list states that all prohibited substances in the S2 class are non-Specified Substances.That last point is worth understanding rather than skimming. Specified status is what can support an athlete's argument that a substance was more likely used for a reason other than performance enhancement. Substances in S0, where our sister site's compound BPC-157 sits, are Specified. Substances in S2, where TB-500 sits, are not. Detection is also mature: doping-control and racing laboratories have published validated methods for the parent peptide and its metabolites in human and equine matrices since 2012.

### Is TB-500 legal to buy?
It is not an approved medicine, so it cannot be legally marketed for human use. It is sold as a research chemical. FDA proposed in July 2026 that it not be added to the list of substances pharmacies may compound; rulemaking is pending.

TB-500 is not an approved drug anywhere in the United States, which means it cannot be lawfully marketed for human use. What exists is a research-chemical market, where products are labelled for laboratory use and sold without any regulatory review of identity, purity or safety.The compounding route is currently closed as well. Pharmacies may compound from bulk substances on FDA's 503A Bulks List; TB-500 is not on it, and in July 2026 FDA proposed that neither the free base nor the acetate be added. That advice is non-binding and rulemaking is pending, but even inclusion would not amount to FDA approval. Athletes have a separate and stricter problem regardless of purchase legality.

### What is actually in a TB-500 vial?
Often not what the label says. A racing laboratory analysed products sold as TB500 and TB1000 and reported content "not systematically consistent with it's former descriptions". FDA flags peptide-related impurities and aggregation.

The published answer is uncomfortable. A French racing laboratory bought products sold as TB500, TB1000 and SGF1000 over the internet and analysed them, concluding that the content of the TB500/TB1000 products was "not systematically consistent with it's former descriptions", and that the third product was mainly sheep extracellular matrix and blood proteins with the purported active ingredient excessively diluted.Racing laboratories also detect non-natural synthesis impurities in plasma after administration of TB4-containing products, which is direct evidence that manufacturing residues travel with these preparations. FDA names peptide-related impurities and aggregation potential as its specific concerns. There is no USP monograph, no pharmaceutical-grade formulation and no validated quality standard for these vials, and a certificate of analysis provided by the seller is a document produced by the seller.

### What dose has TB-500 been used at in research?
In rats, 60 ug/kg/day intraperitoneally for four weeks. In horses, a single 10 mg subcutaneous dose, given by racing laboratories to build detection tests. There is no established human dose.

Two documented in vivo doses exist for the fragment. Rats in the 2026 Achilles tendon study received 60 ug/kg/day intraperitoneally for four weeks. Horses in the racing-laboratory administration studies received a single subcutaneous dose of a TB-500 product containing 10 mg of N-acetylated LKKTETQ, so that detection methods could be validated.There is no established human dose and no published human dose-finding study. Doses used in the full-protein human trials are not transferable: those ran at 42 to 1260 mg intravenously for synthetic thymosin beta-4 and 0.5 to 25 ug/kg for the recombinant protein, of a molecule 5.6 times the mass. Our tools show every published dose with its molecule and species attached and convert nothing between them.

### What is TB-500's half-life?
Unknown in humans; it has never been measured. In rats, the parent peptide converts quickly: Ac-LK dominates at 0 to 6 hours and Ac-LKK is still detectable at 72 hours.

No human half-life exists for TB-500 because no human pharmacokinetic study of the fragment has been published, consistent with FDA identifying no human exposure data at all. Any specific half-life figure quoted on a vendor page has no published source behind it.The animal picture is one of rapid conversion rather than persistence: in rats given TB-500, Ac-LK was the metabolite at highest concentration in the 0 to 6 hour window and Ac-LKK remained detectable to 72 hours. The same study found that only the metabolite Ac-LKKTE showed significant wound-repair activity, and suggested that previously reported activity of TB-500 may belong to that metabolite rather than the parent peptide. The full protein does have published human pharmacokinetics, with half-life increasing with dose across 42 to 1260 mg intravenously, but that is a different molecule.

### Is TB-500 safe?
Nobody knows. FDA states it "lacks important information regarding any safety issues raised by this drug, including whether it would cause harm if administered to humans". Immunogenicity is specifically unassessed.

Unknown, in the literal sense. FDA states that it has not identified any human exposure data for the fragment and that it "lacks important information regarding any safety issues raised by this drug, including whether it would cause harm if administered to humans". There is no human safety dataset to summarise and no published animal toxicology program for this fragment.What has been reported is narrow: no cytotoxicity for the parent peptide or its metabolites in the assays used in the rat metabolism study. The risk FDA names specifically is immunogenicity from aggregation and peptide-related impurities, and the aggregation behaviour of this peptide in marketed vials has not been characterised in any published work. On top of that sits product content: analysis of marketed TB500 and TB1000 found contents that did not consistently match their descriptions. The first study designed to produce human safety data is recruiting now.

### Why does TB-500 keep coming up in horse racing?
Because it was sold as a veterinary preparation and racing laboratories built tests for it. Hong Kong and French racing labs published detection methods and dosed horses with 10 mg to validate them.

Because that is where the product was circulating and where the testing science was done. A 2012 paper from the Hong Kong Jockey Club racing laboratory opens by describing "a veterinary preparation known as TB-500" containing a synthetic version of LKKTETQ, and reports the first identification of the peptide and its metabolites in post-administration samples from horses given a single 10 mg dose. A companion paper detected it in plasma from two thoroughbred geldings after subcutaneous administration.The French racing laboratory published a 2025 population study of endogenous thymosin beta-4 in racing horses, noting that use is forbidden by the IFHA, the FEI and WADA while numerous products claiming to contain the fragment or the protein are available online, and showing that a synthesis impurity is detectable after a single administration. We looked for individual racing-authority disciplinary rulings naming TB-500 and did not verify any against a primary regulator source for this build, so none is cited here.

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30. Certain Bulk Drug Substances for Use in Compounding That May Present Significant Safety Risks (FDA, Human Drug Compounding). Entry: "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500". Content current as of 04/22/2026. https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
31. July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee (FDA Advisory Committee Calendar). https://www.fda.gov/advisory-committees/advisory-committee-calendar/july-23-24-2026-meeting-pharmacy-compounding-advisory-committee-07232026
32. FDA Briefing Document, Pharmacy Compounding Advisory Committee Meeting, July 23-24, 2026 (503A Bulks List: BPC-157, KPV, TB-500, MOTS-c, Emideltide, Epitalon, Semax). https://www.fda.gov/media/193342/download
33. Drugs@FDA (FDA approved-drug database): no approved product containing thymosin beta-4 or TB-500 exists (openFDA API verification queries return NOT_FOUND). https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm
34. PubChem Compound Summary CID 62707662 (TB-500): formula C38H68N10O14, molecular weight 889.0, CAS 885340-08-9, Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH. https://pubchem.ncbi.nlm.nih.gov/compound/62707662
35. PubChem Compound Summary CID 45382195 (thymosin beta-4): formula C212H350N56O78S, molecular weight 4963. https://pubchem.ncbi.nlm.nih.gov/compound/45382195
36. World Anti-Doping Agency: The 2026 Prohibited List. S2.3 Growth Factors and Growth Factor Modulators names "Thymosin-beta4 and its derivatives e.g. TB-500"; S2 is prohibited at all times and all prohibited substances in the class are non-Specified Substances. https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf
37. A Phase 1/2, Randomized, Double-Blind, Placebo-Controlled, Sequential Dose-Escalation Study of TB-500 (Thymosin Beta 4 17-23 Fragment) in Adults With Stable Atherosclerotic Cardiovascular Disease to Evaluate Safety, Tolerability, Pharmacokinetics, and Exploratory Cardiovascular Biomarkers (NCT07487363; recruiting; target n=80; no results posted). https://clinicaltrials.gov/study/NCT07487363
38. ARISE-3: A Multi-Center, Randomized, Double Masked, Placebo Controlled Clinical Study to Assess the Safety and Efficacy of RGN-259 Ophthalmic Solutions for the Treatment of Dry Eye (NCT03937882; completed; n=700; no results posted). https://clinicaltrials.gov/study/NCT03937882
39. ARISE-2: A Multi-Center, Randomized, Double Masked, Placebo Controlled Clinical Study to Assess the Safety and Efficacy of RGN-259 Ophthalmic Solutions for the Treatment of Dry Eye (NCT02974907; completed; n=601; results posted). https://clinicaltrials.gov/study/NCT02974907
40. ARISE-1: A Multi-Center, Randomized, Double Masked, Placebo Controlled Clinical Study to Assess the Safety and Efficacy of RGN-259 Ophthalmic Solutions for the Treatment of Dry Eye (NCT02597803; completed; n=317; no results posted). https://clinicaltrials.gov/study/NCT02597803
41. SEER-1: Phase 3 Study to Assess the Safety and Efficacy of RGN-259 Ophthalmic Solution for the Treatment of Neurotrophic Keratopathy (NCT02600429; terminated, business decision; n=18; results posted). https://clinicaltrials.gov/study/NCT02600429
42. SEER-2: A Phase 3 Study to Assess the Safety and Efficacy of 0.1% RGN-259 Ophthalmic Solution for the Treatment of Neurotrophic Keratopathy (NCT05555589; recruiting; estimated n=70). https://clinicaltrials.gov/study/NCT05555589
43. A Double-Masked, Randomized, Single-Center Study Evaluating the Safety and Efficacy of 0.1% Tbeta4 Ophthalmic Solution Compared to Vehicle on the Signs and Symptoms of Dry Eye in the Controlled Adverse Environment Model (NCT01387347; completed; n=72; results posted). https://clinicaltrials.gov/study/NCT01387347
44. Comparative Study of Thymosin Beta 4 Eye Drops or Vehicle in the Treatment of Patients With Ocular Surface Defects Due to Severe Dry Eye (NCT01393132; completed; n=9; results posted). https://clinicaltrials.gov/study/NCT01393132
45. A Randomized, Double-Mask, Placebo-Controlled, Dose Response, Phase 2 Study of the Safety and Efficacy of Thymosin Beta 4 in the Treatment of Diabetic Patients' Corneal Wounds Resulting From Epithelial Debridement During Vitrectomy (NCT00598871; terminated, slow recruitment; n=12; results posted). https://clinicaltrials.gov/study/NCT00598871
46. A Randomized, Double-Blind, Placebo-Controlled, Dose-Response Study of the Safety and Efficacy of Thymosin Beta 4 in the Treatment of Patients With Venous Stasis Ulcers (NCT00832091; completed; n=72; results posted). https://clinicaltrials.gov/study/NCT00832091
47. A Randomized, Double-Blind, Placebo-Controlled, Dose Response Study of the Safety and Efficacy of Thymosin Beta 4 in the Treatment of Patients With Pressure Ulcers (NCT00382174; completed; n=72; results posted). https://clinicaltrials.gov/study/NCT00382174
48. A Randomized, Double-Blind, Placebo-Controlled, Dose-Response Study of the Safety and Efficacy of Thymosin Beta 4 in the Treatment of Patients With Epidermolysis Bullosa (NCT00311766; terminated, lack of patient availability and expiration of study drug; n=30; results posted). https://clinicaltrials.gov/study/NCT00311766
49. CELEB: A Study to Evaluate the Efficacy and Safety of RGN-137 Topical Gel in Subjects With Junctional and Dystrophic Epidermolysis Bullosa (NCT03578029; terminated, business decision; n=4; no results posted). https://clinicaltrials.gov/study/NCT03578029
50. A Randomized, Double-blind, Placebo-Controlled, Single Dose, Dose-escalation Phase 1a Study of the Safety, Tolerability, Pharmacokinetics and the Potential Immunological Reaction of Recombinant Human Thymosin Beta4 in Chinese Healthy Volunteers (NCT04555824; completed; n=54; no results posted). https://clinicaltrials.gov/study/NCT04555824
51. A Randomized, Double-blind, Placebo-Controlled, Multiple Doses, Dose-escalation Phase 1b Study of the Safety, Tolerability, Pharmacokinetics and the Potential Immunological Reaction of Recombinant Human Thymosin Beta4 in Chinese Healthy Volunteers (NCT04555850; completed; n=30; no results posted). https://clinicaltrials.gov/study/NCT04555850
52. Phase IIa Clinical Study of Efficacy and Safety of Injectable Recombinant Human Thymosin Beta 4 in Patients With Acute Myocardial Infarction (NCT05485818; completed; n=62; no results posted). https://clinicaltrials.gov/study/NCT05485818
53. Efficacy and Safety of Recombinant Human Thymosin beta4 (NL005) for Injection in Patients With Acute Myocardial Infarction: a Phase IIb Clinical Study (NCT05984134; completed; n=90; no results posted). https://clinicaltrials.gov/study/NCT05984134
54. A Randomized, Double-blind, Placebo-Controlled Study of the Safety and Efficacy of RGN-352 in Subjects With an Acute ST Elevation Myocardial Infarction (NCT01311518; withdrawn, "Trial never initiated"; n=0). https://clinicaltrials.gov/study/NCT01311518
55. A Randomized, Double-Blind, Placebo-Controlled, Dose-Response Phase 1 Study of the Safety and Tolerability of the Intravenous Administration of Thymosin Beta 4 and Its Pharmacokinetics After Single and Multiple Doses in Healthy Volunteers (NCT00743769; withdrawn, "Study never initiated due to contract manufacturing issues"; n=0). https://clinicaltrials.gov/study/NCT00743769
56. NL005 recombinant human thymosin beta-4 injection (NCT07586865) https://clinicaltrials.gov/study/NCT07586865