TB-500
TB-500 is a research-market name for a synthetic peptide built on the actin-binding region of thymosin β4, a 43-residue, N-terminally acetylated peptide encoded by TMSB4X that is widely distributed and present at high intracellular concentration in many mammalian cell types. Analytical characterisation of commercial TB-500 identified its active ingredient as the N-terminally acetylated 17-23 fragment Ac-LKKTETQ rather than the intact 43-residue peptide, and a later mass-spectrometric analysis of internet-sold TB500 and TB1000 preparations found their contents were not systematically consistent with the descriptions under which they were sold. This distinction matters when reading the literature: the published pharmacology cited here, including every clinical trial, used full-length thymosin β4, whereas the work done on the fragment itself is metabolism and doping-control analysis. Neither the full-length peptide nor the fragment is approved by any regulator for any indication, and sports-medicine reviews report that both remain banned substances in sport. LC-MS methods for Ac-LKKTETQ and its metabolites have been described and applied to equine urine and plasma after TB-500 administration and to urine from TB-500-dosed rats, with a detection strategy proposed for human plasma and urine.
Information on this page is provided for laboratory research reference. The compound is not a drug, supplement, or medical product, and is not for human or veterinary use, ingestion, or consumption.
- #171251 · 10 mg99.066%
Each result applies to the tested sample shown, not to every catalog strength or lot.
Thymosin β4's established biochemical function is intracellular: it binds monomeric G-actin in a 1:1 complex and inhibits salt-induced polymerisation, and it is the peptide that holds the bulk of the unpolymerised actin in resting human platelets, its widespread distribution and high intracellular concentration suggesting a comparable role in many other cell types. Beyond actin, it forms a functional complex with PINCH and integrin-linked kinase that activates the survival kinase Akt, and it is the precursor of Ac-SDKP, an anti-inflammatory and antifibrotic tetrapeptide released from its N-terminus by sequential hydrolysis by meprin-α and prolyl oligopeptidase. In TNF-α-stimulated human corneal epithelial cells in culture it suppresses NF-κB p65 phosphorylation, nuclear translocation and DNA binding, and in ischaemic mouse myocardium its protective effect is abolished by ErbB2 inhibition, implicating ErbB2/Raf1 signalling. Which of these accounts for the effects of peptide given from outside the cell is not settled — no cell-surface receptor has been established, and metabolite work on the Ac-LKKTETQ fragment suggests some activity attributed to the parent belongs to its breakdown products.4,7,8,9,10,11
Binds G-actin stoichiometrically in a 1:1 complex and inhibits salt-induced polymerisation; identified as identical to the platelet actin-sequestering peptide Fx, which accounts for the bulk of unpolymerised actin in resting human platelets.7,9
Forms a functional complex with PINCH and ILK, activating Akt; after coronary artery ligation in mice, treatment upregulated cardiac ILK and Akt activity alongside enhanced early myocyte survival.9
In TNF-α-stimulated human corneal epithelial cells, reduces nuclear p65 protein, p65 phosphorylation and NF-κB consensus-oligonucleotide binding, and blocks p65 nuclear translocation.10
RNA-seq of ischaemia-reperfusion mouse hearts implicated ErbB signalling; in hypoxia-reoxygenated HL-1, neonatal mouse cardiomyocyte and H9C2 cells the peptide activated ErbB2/Raf1 and suppressed pro-apoptotic Bad, and ErbB2 inhibition abolished its protection in vivo.11
Proteolytic product rather than a target: released from the thymosin β4 N-terminus by meprin-α followed by prolyl oligopeptidase, and significantly reduced by Tβ4 knockdown in the mouse heart; injected Ac-SDKP did not rescue Tβ4-mutant hearts but significantly enhanced endothelial differentiation from adult epicardium-derived precursor cells.8,12
Tissue repair
In a randomised, double-blind, placebo-controlled trial in 96 patients with ST-segment elevation myocardial infarction treated by primary PCI, infarct area at 90 days did not differ significantly between recombinant human thymosin β4 and placebo across the full cohort; the difference reached significance only in the 43 patients whose first dose came within 8 hours of PCI.11
In a single-centre phase 2 trial, 72 adults with moderate-to-severe dry eye were randomised 1:1 to 0.1% thymosin β4 eye drops or placebo for 28 days. Neither primary endpoint (ocular discomfort or inferior corneal staining at day 29) separated from placebo; discomfort during the day-28 controlled adverse environment challenge fell 27% relative to placebo (P=0.0244) and central and superior corneal staining improved (P=0.0075 and P=0.0210).13
In a 56-day multicentre phase 2 trial in 9 patients with severe dry eye, including graft-versus-host-associated disease, the 0.1% thymosin β4 group (12 eyes) showed a 35.1% reduction in ocular discomfort (P=0.0141) and a 59.1% reduction in total corneal fluorescein staining (P=0.0108) versus vehicle control (6 eyes) at day 56, 28 days after dosing stopped.14
In rats dosed with TB-500 and in parallel fibroblast cultures, Ac-LK was the highest-concentration urinary metabolite over 0-6 hours and Ac-LKK remained detectable to 72 hours; in a fibroblast wound-healing assay only the metabolite Ac-LKKTE, not the intact Ac-LKKTETQ, produced significant activity versus control, with no cytotoxicity from parent or metabolites.4
In mice given bilateral fibular osteotomies, intraperitoneal thymosin β4 at 6 mg/kg produced fracture calluses with 41% greater peak force to failure (P<0.01) and about 25% greater stiffness (P<0.05) than saline-treated controls, with 18% more new mineralised tissue and 26% more highly mineralised tissue by micro-CT at 21 days.15
Skin & matrix
In a double-blind, placebo-controlled dose-escalation phase 2 study that randomised 73 patients with venous stasis ulcers across eight European sites (five in Italy, three in Poland) to topical thymosin β4 or placebo, the safety profile at all doses was judged acceptable and comparable to placebo, and complete wound healing within three months was achieved in about 25% of patients — particularly those with small-to-moderate or mild-to-moderate wounds — with the investigators describing the 0.03% concentration as having potential to accelerate healing rather than a demonstrated advantage over placebo.16
In a rat full-thickness dermal wound model, thymosin β4 given topically or intraperitoneally increased re-epithelialisation by 42% over saline controls at 4 days and by up to 61% at 7 days, with at least 11% greater wound contraction by day 7 and increased collagen deposition and angiogenesis; in a Boyden chamber assay 10 pg stimulated keratinocyte migration 2-3-fold over medium alone.17
Cognition & neuroprotection
In male Wistar rats subjected to embolic middle cerebral artery occlusion and randomised to control or thymosin β4 at 2, 12 or 18 mg/kg (10 per group) beginning 24 hours after occlusion, the 2 and 12 mg/kg arms improved neurological outcome versus control from day 14 through day 56 (P<0.05) while the 18 mg/kg arm did not, a non-monotonic dose-response.18
In rats with mild compression spinal cord injury treated intraperitoneally with thymosin β4, Basso-Beattie-Bresnahan locomotor scores and footprint analysis improved over saline controls, myelin basic protein was 57.8% higher and the activated microglia/macrophage marker ED1 was 36.9% lower at 7 days post-injury, alongside reduced pro-inflammatory cytokine transcripts, higher IL-10 mRNA and a smaller lesion cavity.19
What investigators recorded alongside the results above, at the rates their papers state.
No human study of TB-500 itself (the Ac-LKKTETQ fragment) has been published; all clinical safety experience here comes from full-length thymosin β4. Independent narrative reviews in sports medicine report that rigorous human safety data for unapproved peptides of this class are scarce with potential for serious harm to patients, that human orthopaedic data for TB-4 and TB-500 are lacking, and that both remain banned substances in sport.5,6
Not established — no human study of the marketed fragment has been published
Product-identity risk: mass-spectrometric analysis of internet-sold TB500 and TB1000 preparations found their contents were not systematically consistent with the descriptions under which they were sold, in products lacking any EMA or FDA approval and any official manufacturing control2
Reported as a finding across the sampled products rather than as a patient-level rate
Tolerability of full-length thymosin β4 was consistently reported as mild across four trials spanning two designs — two phase 1 intravenous studies in healthy volunteers and two phase 2 topical studies in patients. In the phase 1 study of synthetic Tβ4, treatment-emergent adverse events were all mild or moderate with no dose-limiting toxicities and no serious adverse events; the first-in-human phase 1 study of recombinant human Tβ4 (NL005) likewise reported adverse events mild to moderate in intensity with no dose-limiting toxicities and no serious adverse events, alongside anti-drug antibody monitoring and no marked accumulation on repeat dosing. In the phase 2 dry eye trial no adverse events were observed on any ocular safety measure, including visual acuity, slit-lamp examination, intraocular pressure, dilated funduscopy and corneal sensitivity, and in the phase 2 dose-escalation venous stasis ulcer study the safety profile of topical thymosin β4 at all administered doses was judged acceptable and comparable to placebo.13,16,20,21
Phase 1 intravenous synthetic Tβ4: reported as infrequent and mild or moderate across four cohorts of 10 healthy subjects each (40 in total), randomised to placebo or synthetic Tβ4 at 42, 140, 420 or 1260 mg, given as a single intravenous dose and then the same dose daily for 14 days. Phase 1 recombinant human Tβ4 (NL005): as reported across 54 subjects in seven single-dose cohorts (0.05-25.0 μg/kg) and 30 subjects in three multiple-dose cohorts (0.5, 2.0, 5.0 μg/kg) dosed for 10 days, 84 subjects in total with 28-day observation. Phase 2 dry eye: none reported by any of the 72 randomised subjects over 28 days of topical 0.1% thymosin β4 ophthalmic solution or placebo. Phase 2 venous stasis ulcers: as reported across the 73 randomised patients; that source reports no event-level rates and no dose-specific safety signal.
Preclinical oncological signal: thymosin β4 is overexpressed in a wide variety of cancers including colorectal carcinoma and has been proposed as a therapeutic target there, and silencing it suppressed tumour growth in mouse models — consistent with a tumour-supporting role in those models.22
Not an incidence — in nude mice bearing CT-26 mouse colorectal tumours, adenoviral shRNA knockdown of thymosin β4 markedly reduced tumour growth and induced apoptosis; no human data address the converse risk of administered peptide
- 1.Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential. · Drug Testing and Analysis · 2012 · PMID 22962027
- 2.TB500/TB1000 and SGF1000: A scientific approach for a better understanding of misbranded and adulterated drugs. · Drug Testing and Analysis · 2023 · PMID 36482504
- 3.Doping control analysis of TB-500, a synthetic version of an active region of thymosin β₄, in equine urine and plasma by liquid chromatography-mass spectrometry. · Journal of Chromatography A · 2012 · PMID 23084823
- 4.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 · 2024 · PMID 38382158
- 5.Injectable Peptide Therapy: A Primer for Orthopaedic and Sports Medicine Physicians. · The American Journal of Sports Medicine · 2026 · PMID 41476424
- 6.Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance. · Sports Medicine · 2026 · PMID 41966639
- 7.Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable. · The Journal of Biological Chemistry · 1991 · PMID 1999398
- 8.The anti-inflammatory peptide Ac-SDKP is released from thymosin-β4 by renal meprin-α and prolyl oligopeptidase. · American Journal of Physiology. Renal Physiology · 2016 · PMID 26962108
- 9.Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. · Nature · 2004 · PMID 15565145
- 10.Thymosin beta 4 suppression of corneal NFkappaB: a potential anti-inflammatory pathway. · Experimental Eye Research · 2007 · PMID 17254567
- 11.Recombinant human thymosin beta 4 improves ischemic cardiac dysfunction in mice and patients with acute ST-segment elevation myocardial infarction after reperfusion. · Cardiovascular Research · 2025 · PMID 41229390
- 12.Thymosin beta4 induces adult epicardial progenitor mobilization and neovascularization. · Nature · 2007 · PMID 17108969
- 13.Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, Phase II clinical trial conducted using the controlled adverse environment (CAE™) model. · Clinical Ophthalmology · 2015 · PMID 26056426
- 14.Thymosin β4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. · Cornea · 2015 · PMID 25826322
- 15.Thymosin β4 administration enhances fracture healing in mice. · Journal of Orthopaedic Research · 2014 · PMID 25042765
- 16.The effect of thymosin treatment of venous ulcers. · Annals of the New York Academy of Sciences · 2010 · PMID 20536470
- 17.Thymosin beta4 accelerates wound healing. · The Journal of Investigative Dermatology · 1999 · PMID 10469335
- 18.A dose-response study of thymosin β4 for the treatment of acute stroke. · Journal of the Neurological Sciences · 2014 · PMID 25060418
- 19.Beneficial effects of thymosin β4 on spinal cord injury in the rat. · Neuropharmacology · 2014 · PMID 24937047
- 20.A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. · Annals of the New York Academy of Sciences · 2010 · PMID 20536472
- 21.A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin β4 in healthy Chinese volunteers. · Journal of Cellular and Molecular Medicine · 2021 · PMID 34346165
- 22.In vivo growth suppression of CT-26 mouse colorectal cancer cells by adenovirus-expressed small hairpin RNA specifically targeting thymosin beta-4 mRNA. · Cancer Gene Therapy · 2014 · PMID 25124811