Research brief

TB-500

Also written as Thymosin beta-4 fragment (LKKTETQ), often sold as thymosin beta-4

Evidence read from: ClinicalTrials.gov, PubMed, FDA, SEC filings · how we work · Last reviewed 9 August 2026

The case for TB-500 is built on a substitution that almost nobody notices. Thymosin beta-4 is a 43 amino acid protein with genuine, replicated biology and a real clinical development history. TB-500 is a seven amino acid synthetic fragment of it. Roughly 84 percent of the parent molecule is missing from what people inject, including the entire region carrying much of its anti-fibrotic activity.

Marketed for

Tendon, ligament and muscle repair; injury recovery; flexibility.

Evidence reviewed

9 August 2026, against 29 sources

Human evidence

Graded, for members. See the membership

If you read nothing else

• •TB-500 is not thymosin beta-4. It is an acetylated seven-residue fragment, Ac-LKKTETQ, corresponding to residues 17 to 23. This was established by mass spectrometry of an actual marketed product in 2012, and the FDA names the substance exactly that way.
• •Not one human trial, at any phase, anywhere in the trial registry, has tested injected thymosin beta-4 or TB-500 for tendon, ligament, muscle or athletic recovery. That is the indication it is sold for.
• •The three largest human trials of thymosin beta-4, covering roughly 1,600 people, all missed their primary endpoints. None of the three was ever published in a peer-reviewed journal; the results are documented only in the company’s regulatory filings.
• •Both trials of injected systemic thymosin beta-4 by that company were withdrawn with zero patients enrolled, after a manufacturing-compliance clinical hold in 2011.
• •The only pharmacokinetic study of TB-500 concluded the wound-healing activity may belong to a breakdown product rather than to the peptide people inject. Its opening sentence states that TB-500’s biological effects "have not been documented".
• •The FDA states it "has not identified any human exposure data" for TB-500 and "lacks important information regarding any safety issues raised by this drug". That was still the agency’s published position when we re-checked in August 2026.
• •The compounding rules around TB-500 loosened in 2026 while the evidence stayed where it was. The FDA removed it from its safety-risk list in April, and in July its advisory committee voted 8 to 6 to recommend it for the compounding list, against the agency reviewers’ own recommendation. No trial reported in between.

Five of the sources, and what they say

Open any of them. Each is tagged with the kind of evidence it is, because a randomized trial in people and an experiment in cell culture answer very different questions. This brief was written against 29 sources of this kind.

1. 1.Review
   Goldstein AL, Hannappel E, Kleinman HK. Thymosin beta4: actin-sequestering protein moonlights to repair injured tissues. Trends Mol Med. 2005;11:421-429. PMID 16099219. Open source
2. 2.Review
   Hannappel E. Beta-thymosins. Ann N Y Acad Sci. 2007;1112:21-37. PMID 17468232. Open source
3. 3.In vitro
   Sosne G, Qiu P, Goldstein AL, Wheater M. Biological activities of thymosin beta4 defined by active sites in short peptide sequences. FASEB J. 2010;24:2144-2151. PMID 20179146. Open source
4. 4.Analytical
   Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P. Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500. Drug Test Anal. 2012;4:733-738. PMID 22962027. Open source
5. 5.Animal
   Rahaman KA, Muresan AR, Min H, et al. Simultaneous quantification of TB-500 and its metabolites in in-vitro experiments and rats. J Chromatogr B. 2024;1235:124033. PMID 38382158. Open source

Members read on

The grade and the full review are for members

The findings above are free, and so are the sources. Behind this line is our grade for the human evidence on TB-500, the full review, what we looked for and could not find, and all 29 sources with the kind of evidence each one is.

The grade is our judgment, and the review is the working behind it: what has actually been run in people, what it measured instead, who ran it, who paid for it, and which results were never published at all. Our findings are above and our sources are open, so nothing here asks you to take the reasoning on trust. What a membership buys is where we land, and why.

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