What is TB-500? Most people will tell you it's thymosin beta-4, or a synthetic copy of it. But TB-500 started out as the name on a horse product that didn't even list what was inside. It still isn't the official name of any one molecule.
TB-500 is a name, not a molecule
A drug sold in the US normally carries an official generic name, called a USAN, that pins it to one specific substance. TB-500 doesn't have one. The FDA calls it "a common name" and says it has found more than one molecule sold under it. Today the name usually means a synthetic seven-amino-acid piece of thymosin beta-4 with a small chemical cap on one end. Usually.
The proof: what is TB-500, really? Follow the paper trail
Let's get into it.
It started with a mystery label. A product called TB-500 was sold for horses as "the synthetic peptide of the active region of thymosin-beta 4." No amino acid sequence. No molecular weight. That's how a Ghent University project funded by the World Anti-Doping Agency (WADA) described it (WADA, project 13D34PV). The FDA's 2026 review dates the horse product to 2011 and says it was sold into horse and greyhound racing (FDA briefing document, July 2026).
Doping labs figured out what was in it. In 2012 the Ghent lab ran TB-500 through mass spectrometry and found Ac-LKKTETQ, amino acids 17 to 23 of thymosin beta-4 with an acetyl cap on the front end (Esposito et al., Drug Test Anal 2012). The Hong Kong Jockey Club's lab published a test for it in horses that same year (Ho et al., J Chromatogr A 2012). The first TB-500 papers came from labs that weren't trying to study it. They were trying to catch it.
Then the name drifted. In 2023 a French horse-racing lab analyzed TB500 products sold online and found the contents weren't always consistent with how they'd been described (Delcourt et al., Drug Test Anal 2023). A 2025 eye-research paper used "TB500" for the uncapped sequence, built into a gel (Lu et al., ACS Appl Mater Interfaces 2025). Same name. Different chemistry.
A lot of "TB-500 research" is borrowed. The pharmacy that asked the FDA to allow TB-500 for compounding cited three papers. Two tested the uncapped fragment, not TB-500, and none gave TB-500 to people. The FDA noted that results for the uncapped version "cannot be directly extrapolated" to the capped one (FDA briefing document).
So why should you care? Read the methods, not the title. A 2026 rat study on Achilles tendon repair calls its compound "synthetic thymosin beta-4 (TB-500)." The methods name a catalog item from a peptide seller. There's no sequence, no molecular weight and no identity test anywhere in the paper (Biçer et al., Jt Dis Relat Surg 2026). From the paper alone, you can't tell which molecule was tested.
"Is TB-500 banned?" In sport, yes. WADA's 2026 Prohibited List names "Thymosin-ß4 and its derivatives e.g. TB-500" in a class that's prohibited at all times (WADA 2026 list). With the FDA it's a pharmacy question. In July 2026 an FDA advisory committee voted to recommend TB-500 for the compounding list, even though FDA staff had recommended against it (AJMC, July 2026). That vote is non-binding, and as of October 2026 the FDA hasn't acted on it.
The big learning lesson
Keep reading: TB-500 vs thymosin beta-4 · Why BPC-157 and TB-500 are studied together · The FDA "peptide ban" of 2026, explained
Frequently asked questions
What is TB-500?
TB-500 is a common name, not an official drug name. It usually means Ac-LKKTETQ, a synthetic seven-amino-acid fragment of thymosin beta-4 with an acetyl cap, which PubChem lists at about 889 daltons.
Is TB-500 banned?
In sport, yes. WADA prohibits thymosin beta-4 and its derivatives, naming TB-500, at all times. It isn't FDA approved, and the July 2026 advisory vote to recommend it for pharmacy compounding is non-binding.
Has TB-500 been studied in humans?
The FDA's 2026 review found no published studies of TB-500 given to people. The first registered human trial started recruiting in February 2026 and has no published results yet.