TB-500: a fragment with a borrowed reputation, and the fine print

The short version: TB-500 is built from thymosin beta-4, a 43-amino-acid protein found in nearly every cell. What doping labs and the US FDA describe under that name is a small piece of it: seven amino acids with an acetyl cap on the front. Most of the research quoted for TB-500, from rat wounds to eye drops, used the whole protein. When FDA reviewers searched in 2026, they found no study that had given TB-500 to people.

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The protein it comes from

Thymosin beta-4, often written Tβ4, was first isolated from calf thymus, hence the name. It later turned up in almost every cell type and in fluids such as blood, saliva and tears. Inside cells it stores actin, the protein cells string into filaments for their internal frame, until a cell needs it, for instance to move.

A 2010 review mapped which parts of it seem to do what. Four amino acids at the very start are tied to damping down inflammation and scarring. The seven at positions 17 to 23, LKKTETQ, take in the actin-binding region, and lab studies connect that stretch with cells migrating, blood vessels sprouting and wounds closing. Some effects haven’t been traced to any one part.

So what is TB-500?

The name comes from the racing world. A 2012 report from the Hong Kong Jockey Club’s laboratory said that a veterinary product called TB-500 was built around LKKTETQ with an artificial acetyl cap, and published a way to catch it in horses. FDA says the product was marketed for horse and greyhound racing.

Here’s the catch. TB-500 is a trade name, not an official drug name. FDA’s reviewers had come across several salts and related molecules, including different active compounds, all sold as TB-500. Many websites also use the name as if it meant thymosin beta-4. It doesn’t. FDA puts the fragment’s molecular weight at about 889, while the full protein is around 5 kDa, more than five times heavier. The mass on a COA tells you which one you have.

The famous studies used the whole protein

The best-known animal studies used thymosin beta-4, not TB-500. In 1999 an NIH team found that thymosin beta-4 sped up healing of deep skin wounds in rats, with skin regrowth over the wound up to 61% higher than with saline by day 7. In 2004 a Dallas group reported in Nature that it improved heart function in mice after a coronary artery was tied off.

The short sequence has a little evidence of its own. A 2003 study found that a synthetic LKKTETQ peptide improved wound repair in elderly mice about as well as the full protein. But it had no acetyl cap, and FDA’s reviewers noted that acetylation changes how a peptide behaves, so those results don’t carry straight over to TB-500.

When a Korean doping lab tested TB-500 itself in 2024, on scratched layers of fibroblasts, the cells that make connective tissue, the gaps closed no faster than in the controls. One breakdown product, Ac-LKKTE, did speed closure. The authors suggest past healing results credited to TB-500 may belong to that smaller piece.

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One rat study of TB-500 itself

FDA’s reviewers found no animal study testing TB-500 for healing. In July 2026 a Turkish team repaired the Achilles tendons of 32 rats and compared no treatment, BPC-157, TB-500 and the two together. The TB-500 tendons needed significantly more force to snap than the untreated ones. Combining the peptides added nothing, which matters for the Wolverine blend that pairs them. It’s one small study, and its abstract calls TB-500 “synthetic thymosin beta-4”, a sign of how loosely the name gets used. Our BPC-157 article covers the other half of that pair.

What has been tested in people

Thymosin beta-4 has been through real trials. TB-500 hasn’t.

For TB-500, FDA’s May 2026 review found no clinical studies, case reports or human exposure data, and called its safety in people unknown. The later dental report’s mix also held BPC-157, ARA-290, a steroid and a local anaesthetic, and the authors say they can’t establish what caused the recovery.

If you remember one thing: most of what’s said about TB-500 comes from studies of thymosin beta-4, the full protein. TB-500 itself has one rat healing study and a three-person case report.

Where the evidence stops

• No trial in people. The one ClinicalTrials.gov record with TB-500 in its title, posted in March 2026, describes itself as a fictional example.
• No safety studies. FDA found no animal toxicity or cancer studies, and flagged a possible immune reaction when injected, a risk it said clumping and impurities could amplify.
• Banned in sport. WADA’s 2026 Prohibited List names thymosin beta-4 and its derivatives, TB-500 included, under S2.3, prohibited at all times. In 2016 the Court of Arbitration for Sport gave 34 Essendon AFL players two-year bans over thymosin beta-4.
• Not registered in South Africa. SAHPRA’s May 2026 public warning names TB-500 among illegally marketed peptides.

A note on framing

Most of the evidence above is about a bigger molecule, tested under medical supervision. None of it transfers automatically to TB-500, a batch of research material, or anyone’s own use. We sell to researchers, and FDA’s review is a better read than any forum post.

Where JP fits

JP Research supplies TB-500 in two vial sizes as research-grade lyophilised powder, for laboratory research use only. It’s also half of the Wolverine blend. Our reconstitution and storage guide covers handling, and our guide to reading a COA explains what to check on a lab report.

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Sources

• US FDA: TB-500 briefing for its compounding advisory committee (May 2026)
• Sosne et al.: Active sites of thymosin beta4 (FASEB J, 2010)
• Ho et al.: Doping control analysis of TB-500 in horses (J Chromatogr A, 2012)
• Malinda et al.: Thymosin beta4 accelerates wound healing (J Invest Dermatol, 1999)
• Bock-Marquette et al.: Thymosin beta4 and cardiac repair (Nature, 2004)
• Philp et al.: The actin binding site on thymosin beta4 (FASEB J, 2003)
• Philp et al.: Tβ4 and its actin-binding peptide in mouse wounds (Wound Repair Regen, 2003)
• Rahaman et al.: TB-500 metabolites and wound-healing screening (J Chromatogr B, 2024)
• Biçer et al.: BPC-157 and TB-500 in rat Achilles healing (Jt Dis Relat Surg, 2026)
• ClinicalTrials.gov: ARISE-2 (NCT02974907)
• ClinicalTrials.gov: ARISE-3 (NCT03937882)
• Sosne et al.: RGN-259 in neurotrophic keratopathy, SEER-1 (Int J Mol Sci, 2022)
• Zhang et al.: Recombinant thymosin beta 4 after heart attack (Cardiovasc Res, 2025)
• Froum et al.: Peptides for nerve injury, three cases (Front Oral Health, 2026)
• ClinicalTrials.gov: NCT07487363
• WADA: 2026 Prohibited List
• AFL.com.au: Court bans the Essendon 34 (January 2016)
• SAHPRA: Peptide products, public information (May 2026)