TB-500

TB-500 is the name used for a short synthetic peptide with the sequence Ac-LKKTETQ: seven amino acids with an acetyl group on the first one. Researchers at Ghent University identified this acetylated 17–23 fragment of human thymosin beta-4 as the active content of products sold as TB-500, and synthesised it as a reference standard for anti-doping tests ^[2]. The FDA uses the same description, “thymosin beta-4, fragment (LKKTETQ), also known as TB-500” ^[12].

Thymosin beta-4 (Tβ4) is a natural 43-amino-acid protein. It was first isolated from calf thymus and its full sequence was published in 1981 ^[1]. It is one of the main proteins that bind actin, the building block of the cell’s internal skeleton ^[5]. The LKKTETQ stretch sits inside Tβ4’s actin-binding region, which is why it was chosen as a small stand-in for the whole protein ^[3].

This distinction matters. TB-500 is not the same molecule as thymosin beta-4, and results obtained with one cannot simply be assumed for the other. Throughout this page we say which molecule each study used. TB-500 is often discussed alongside BPC-157, which is an unrelated peptide, and it should not be confused with thymosin alpha-1, a different thymus-derived peptide with an immune role.

Full-length thymosin beta-4 binds and holds individual actin units, which affects how cells change shape and move. In laboratory and animal work it stimulated migration of skin cells (keratinocytes) and increased new blood-vessel formation and collagen deposition in wounds ^[4]. In the heart, a 2004 Nature study found that Tβ4 formed a complex with the proteins PINCH and integrin-linked kinase, activated the survival signal Akt, and improved heart-muscle survival and function after induced heart attacks in mice ^[5].

Whether the seven-amino-acid fragment reproduces these effects is less clear. In a 2003 study from the US National Institutes of Health, the synthetic peptide LKKTETQ (without the acetyl group) promoted skin-wound repair in aged mice to a degree comparable with full-length Tβ4 ^[3]. A 2024 study that tracked how TB-500 is broken down found that its main metabolite in rats was the fragment Ac-LK, and that in cultured fibroblasts only the metabolite Ac-LKKTE, not TB-500 itself, significantly improved wound closure. The authors suggested that wound-healing activity attributed to TB-500 may come from this metabolite ^[6].

Much of the wound-healing literature uses full-length Tβ4. In a 1999 rat study, Tβ4 applied to the skin or injected into the abdomen increased re-epithelialisation of full-thickness wounds by 42% over saline at four days and by up to 61% at seven days, and treated wounds contracted at least 11% more ^[4]. The 2003 NIH study extended this to diabetic and aged mice, and is the main published animal evidence that the LKKTETQ fragment itself has wound-healing activity ^[3].

Heart research, again with full-length Tβ4, has attracted wide attention because of the 2004 mouse study described above ^[5]. None of this cardiac work used TB-500.

Direct studies of TB-500 are few. The clearest is a 2026 rat study from Turkey in which 32 rats had their Achilles tendons cut and repaired, then received a product described as TB-500 (60 µg/kg/day), BPC-157 (10 µg/kg/day), both, or nothing for four weeks. The TB-500 group had significantly higher maximum load to failure than controls and better tissue scores on two histology scales; combining the two peptides gave no extra benefit ^[7]. It was a small, exploratory study, and the authors called for dose-finding and longer-term work.

A 2026 Sports Medicine review of peptides marketed for injuries and performance, which covered both Tβ4 and TB-500, concluded that many unapproved peptides show favourable repair outcomes in animals but that rigorous human safety data are scarce ^[11].

We found no published human trial of TB-500. The human trials that exist used full-length synthetic thymosin beta-4, usually given at doses and by routes quite different from those discussed online.

In a phase 1 randomised, placebo-controlled study, healthy volunteers received intravenous Tβ4 at 42, 140, 420 or 1,260 mg as a single dose and then daily for 14 days. Adverse events were infrequent and mild or moderate, with no dose-limiting toxicity or serious adverse events ^[8]. In a phase 2 double-blind trial in 73 patients with venous leg ulcers across eight European sites, topically applied Tβ4 had a safety profile comparable to placebo; the authors reported that a 0.03% strength “may have the potential” to speed healing ^[9]. In a small phase 2 eye study, nine patients with severe dry eye used 0.1% Tβ4 eye drops (RGN-259) or vehicle six times a day for 28 days, with statistically significant improvements in discomfort and corneal staining in the treated group ^[10].

These results are for a different, much larger molecule and do not show that TB-500 is effective or safe.

TB-500 itself: the 2026 rat tendon study used 60 µg/kg/day by intraperitoneal injection for four weeks ^[7]. This is an animal dose, and no human dose of TB-500 has been established.

Full-length thymosin beta-4 (not TB-500): the phase 1 study used 42 mg to 1,260 mg intravenously, once or daily for 14 days ^[8]; the venous ulcer trial tested topical strengths including 0.03% ^[9]; and the dry eye trial used 0.1% eye drops six times daily ^[10]. These figures describe what studies used, are not recommendations, and should not be transferred to TB-500. For converting vial contents to a concentration, see the peptide calculator.

There are no human safety data for TB-500. The reassuring phase 1 and 2 safety findings apply to pharmaceutical-grade full-length Tβ4 given under trial conditions ^{[8] [9] [10]}. The FDA has said that compounded TB-500 may carry a risk of immune reactions (immunogenicity) for some routes of administration and of peptide-related impurities ^[12].

Product quality is a specific concern. A 2023 analysis by French anti-doping researchers found that the contents of products sold online as TB500 and TB1000 were not consistently what their descriptions claimed ^[13]. Without independent testing, buyers cannot assume a vial contains what its label states.

TB-500 is not approved as a medicine anywhere we are aware of. In the US, the FDA previously placed “thymosin beta-4, fragment (LKKTETQ), also known as TB-500” in category 2 of its interim compounding policy, the list of bulk substances that may present significant safety risks; the nomination was later withdrawn and the FDA now lists it among substances previously in category 2 ^[12]. On 23 July 2026, the FDA’s Pharmacy Compounding Advisory Committee considered TB-500; STAT reported that it voted to recommend adding TB-500 to the list of substances US pharmacies may compound. The FDA had not posted the votes when we checked, the vote is not binding, and as of September 2026 we have not confirmed a final FDA decision ^[14].

The World Anti-Doping Agency lists “thymosin-β4 and its derivatives, e.g. TB-500” under S2 (peptide hormones, growth factors and related substances), so it is prohibited at all times for athletes in WADA-compliant sport ^[15]. Country-level rules on buying research peptides are covered on our legal status pages, including the UK page.

TB-500 is sold as a freeze-dried powder. As with other peptides, the dry powder is generally kept cold, dry and away from light, and reconstituted solutions are refrigerated and used within a limited time. See how to store peptides for general principles.

Because products labelled TB-500 vary in what they contain, independent testing matters more than usual. You can compare prices, read our guide on how to read a COA, and filter for third-party tested suppliers.