TB-500
A synthetic seven-residue peptide corresponding to an acetylated fragment of the protein thymosin beta-4, sold for soft-tissue and tendon repair. It is routinely marketed as thymosin beta-4 itself, and the two names are used interchangeably almost everywhere, but they are not the same molecule: one is a 43-residue protein, the other a capped fragment of it. Almost everything indexed under the name TB-500 is anti-doping analytical chemistry, not therapeutic research.
Leu-Lys-Lys-Thr-Glu-Thr-Gln · 7 residues · 889.02 Da (computed)
Lysine at position 2, 3 (internal).
Mechanism
Claimed
Accelerates repair of muscle, tendon, ligament and other soft tissue by binding actin, promoting cell migration and stimulating angiogenesis — the functions attributed to its parent protein, thymosin beta-4.
Actually established
Nothing has been established in humans.
How good is the evidence
There is no human study of TB-500 in the indexed literature, and no animal study measuring a healing outcome. What exists is analytical chemistry: doping-control laboratories characterising the molecule, developing assays for it in human and equine samples, and mapping its metabolites. The single paper that tested biological activity did so in cultured fibroblasts and found the effect in a metabolite rather than in TB-500 itself. The evidence base people cite for this compound belongs to a different molecule, its parent protein.
The literature is concentrated by discipline rather than by author: nearly every indexed paper naming TB-500 comes from a sports anti-doping laboratory (Ghent, Hong Kong, Seoul, Cologne). No pharmaceutical or clinical research programme has published on it, which is itself the most informative fact about the evidence base.
Claims, one at a time
Each claim carries its own evidence tier. A compound is never simply "well studied" — some of its claims may be, others not at all.
| Claim | Verdict | Evidence | Basis |
|---|---|---|---|
| TB-500 is thymosin beta-4 | contradicted | Mechanistic | Mass spectrometry on a product sold as TB-500 identified the N-terminally acetylated 17-23 fragment of human thymosin beta-4, not the full protein; a second laboratory describes TB-500 in its title as a synthetic version of an active region of thymosin beta-4. The names are used interchangeably in vendor material and in forum discussion, and the substitution matters, because the human and animal evidence usually offered for TB-500 was generated with the protein. |
| Accelerates healing of muscle, tendon and ligament injuries | mixed | In vitro | The only indexed test of biological activity was a fibroblast scratch assay run alongside a metabolism study. The parent peptide did not show significant wound-healing activity in that assay; one metabolite did. That is a single in-vitro result in one cell type, and no animal or human study has measured healing of an actual injury after TB-500 administration. |
| Works in people, with athletes and clinicians using it for recovery | untested | Mechanistic | No human trial of TB-500 for any indication was found in the indexed literature. Human sample analysis exists, but only in the anti-doping context of detecting the substance — detection methods establish that people take it, not that it does anything. |
The studies themselves
| Study | Design | Subjects | Quality |
|---|---|---|---|
Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential.
Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P · Drug testing and analysis · 2012
PMID 22962027
|
in_vitro / unknown | Mechanistic
risk of bias: low
| |
Doping control analysis of TB-500, a synthetic version of an active region of thymosin β₄, in equine urine and plasma by liquid chromatography-mass spectrometry.
Ho EN, Kwok WH, Lau MY, Wong AS, Wan TS, Lam KK, Schiff PJ, Stewart BD · Journal of chromatography. A · 2012
PMID 23084823
|
in_vitro / other_animal | — Equine urine and plasma samples | Mechanistic
risk of bias: low
|
Simultaneous quantification of TB-500 and its metabolites in in-vitro experiments and rats by UHPLC-Q-Exactive orbitrap MS/MS and their screening by wound healing activities in-vitro.
Rahaman KA, Muresan AR, Min H, Son J, Han HS, Kang MJ, Kwon OS · Journal of chromatography. B, Analytical technologies in the biomedical and life sciences · 2024
PMID 38382158
|
in_vitro / mixed | — Human serum and enzyme systems in vitro, urine from rats given TB-500, and cultured fibroblasts | In vitro
risk of bias: moderate
|
beta-Thymosins.
Hannappel E · Annals of the New York Academy of Sciences · 2007
PMID 17468232
|
narrative_review / mixed | Mechanistic
risk of bias: unclear
|
- No human study of TB-500 for any indication was found in the indexed literature — not an efficacy trial, not a safety study, not a pharmacokinetic study.
- No animal study measuring a healing outcome after TB-500 administration was found; the one rat study measured metabolite concentrations.
- Whether the wound-healing activity attributed to TB-500 belongs to the administered peptide or to a metabolite is unresolved, and the one comparison found it in the metabolite.
- Human trials of thymosin beta-4 itself say nothing verifiable about TB-500: no study has compared the protein and the fragment head to head for any outcome.
- The C-terminal chemistry of the marketed compound is not established from an independent source.
- No dose from any cited study is recorded here, because no full text has been read.