Thymosin beta-4 is the molecule behind a name most people meet second-hand. Almost everything sold on the peptide market under the healing-and-recovery heading is labelled TB-500, and TB-500 is a seven-amino-acid fragment of this 43-amino-acid protein. The parent protein is the subject of this entry, and it turns out to have something most compounds in this library do not: a real, registered, multi-phase clinical programme.
That programme is for eyes and for hearts. It is not for injuries.
What it is
Thymosin beta-4 is not a drug that someone designed. It is a protein the body already makes, encoded by the gene TMSB4X, present in most human cell types. Its best-established job inside a cell is unglamorous and specific: it binds monomeric actin — G-actin, the free-floating form — and holds it in reserve, so the cell has a pool to draw on when it needs to build or rebuild its internal scaffolding. A molecule that manages the actin supply is a plausible starting point for a story about wound repair and cell migration, and that is the story the market tells about it.
At 43 amino acids it sits exactly on the fuzzy line between a peptide and a protein, and the literature calls it both. What a peptide actually is covers why that line is a convention rather than a rule.
The registered record, counted
On 2026-09-16, ClinicalTrials.gov held 18 interventional studies naming thymosin beta-4, enrolling 2,460 participants in total. For a compound in this library that is a large number — most entries here report zero.
Sorting those 18 by what they were studying is the whole finding:
| What the trials studied | Condition entries | Highest phase |
|---|---|---|
| Eye surface — dry eye disease, neurotrophic keratopathy | 7 | Phase 3 (three studies) |
| Heart — acute myocardial infarction, ischemia, STEMI | 6 | Phase 2 |
| Skin wounds — pressure ulcers, venous stasis ulcers | 2 | Phase 2 |
| Blood vessels — atherosclerotic disease, endothelial dysfunction | 2 | Phase 1/2 |
| Healthy volunteers (safety and pharmacokinetics) | 2 | Phase 1 |
| Tendon, ligament, muscle or sports injury | 0 | — |
Every one of the three phase 3 studies is an eye drop: RGN-259 ophthalmic solution, sponsored by ReGenTree, LLC. The heart studies — sponsored by Beijing Northland Biotech — are phase 2, two of them completed and one not yet recruiting when this entry was written.
The bottom row is the one that matters to anyone who arrived here from a product page. The compound is sold, overwhelmingly, for recovery from tendon and muscle injury. Nobody has registered a trial for that.
Two withdrawn, two terminated
Eighteen registrations is not eighteen completed studies. Two of the records are withdrawn, meaning they never enrolled a participant, and two were terminated before finishing. A registry count measures intent as much as it measures evidence, and reading it as a body of results overstates what is there — a distinction this library applies to every entry that quotes a registry number, including the ones where the number is zero.
Sixteen of the 18 come from three sponsors: ReGenTree (6), RegeneRx Biopharmaceuticals (5) and Beijing Northland Biotech (5). That is a concentrated field. It is not a reason to discount the work, but it does mean the record has not been assembled by many independent groups checking each other.
Published literature
602 PubMed records name thymosin beta-4 in the title or abstract as of 2026-09-16. Of those, 330 carry the human MeSH tag and three carry the randomized-controlled-trial publication type. A large literature with a very small randomized core is the normal shape for a molecule studied first as cell biology and only later as a candidate treatment — most of those 602 papers are about what actin-sequestering proteins do, not about what happens when you give one to a patient.
The fragment, and why the distinction is not pedantry
TB-500 reproduces residues 17 to 23 of this protein — the sequence LKKTETQ, with the front end acetylated — and nothing else. Seven residues out of forty-three.
The reason to insist on the difference is that different regions of this protein do different things. A separate fragment of the same molecule, the four-residue Ac-SDKP, is cut out in the body by an enzyme called prolyl oligopeptidase and acts on inflammation and fibrosis — a genuinely different activity from the region TB-500 copies. So "research on thymosin beta-4" is not automatically research on TB-500, and neither is automatically research on Ac-SDKP. Our entry on TB-500 and what it actually is covers the fragment itself.
One thing did change recently on that side of the ledger. NCT07487363 — a phase 1/2 study of TB-500 itself, described in its own title as the thymosin beta-4 17–23 fragment, looking at cardiovascular biomarkers in stable atherosclerotic disease — was recruiting when this entry was written. It is the first registered trial of the fragment as such, and it is worth noting that it too is a cardiovascular study, not a musculoskeletal one.
Where this leaves a reader
The honest summary is narrow and a little surprising. Thymosin beta-4 has a better clinical record than almost anything else in this library, and that record says nothing about the use it is sold for. Three phase 3 studies exist and they are eye drops. Six heart studies exist and they are phase 2. Zero studies exist for tendons, ligaments and muscles.
An absence in a registry is not proof that something does not work. It is proof that nobody has run the experiment, which is a different and more useful fact — and it is one anyone can check for themselves in a minute. Questions about treatment belong with a clinician, not with a product page or with this one.