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TB-500 vs Thymosin Beta-4 — Fragment vs Full Protein

TB-500 and Thymosin Beta-4 (Tβ4) are often presented as competing compounds. They are not the same molecule: TB-500 is a synthetic fragment of the full-length Tβ4 protein. This page reports what each term identifies, and which studies apply to which molecule.

On this page
  1. 1.Molecule Identity
  2. 2.Human Evidence, by Molecule
  3. 3.Animal Evidence
  4. 4.Evidence Level
  5. 5.FAQ
  6. 6.References

Molecule Identity

Thymosin Beta-4 is a naturally occurring 43-amino-acid protein, encoded by the TMSB4X gene. Esposito et al. 2012 (Drug Test Anal, PMID 22962027), an anti-doping laboratory's high-performance liquid chromatography/mass spectrometry analysis of a commercial TB-500 product, identified TB-500 as the N-terminal acetylated 17-23 fragment of Thymosin Beta-4 (Ac-LKKTETQ) — 7 amino acids, not the full-length protein.

Thymosin Beta-4 (full protein)TB-500 (fragment)
IdentityNaturally occurring 43-amino-acid protein (gene TMSB4X)N-terminal acetylated 17-23 fragment of Thymosin Beta-4 (Ac-LKKTETQ), 7 amino acids
Source confirming thisEndogenous protein, characterized across decades of literatureEsposito et al. 2012 (Drug Test Anal, PMID 22962027) — mass spectrometry of a commercial TB-500 product
Human trialsRegeneRx Phase 2 trials tested native, full-length Thymosin Beta-4: NCT00382174 (pressure ulcers, completed, no benefit over placebo) and NCT00311766 (epidermolysis bullosa, terminated)None identified
Animal evidenceBock-Marquette et al. 2004 (Nature, PMID 15565145), mouse myocardial infarction modelBiçer et al. 2026 (PMID 42542926), rat Achilles-tendon model, dosed as “synthetic thymosin beta-4 (TB-500)” at 60 µg/kg/day
FDA statusNot FDA-approvedNot FDA-approved

Human Evidence, by Molecule

RegeneRx sponsored two Phase 2 trials of native, full-length Thymosin Beta-4: NCT00382174 tested topical Thymosin Beta-4 for pressure ulcers, completed with results posted in 2010 showing no wound-healing benefit over placebo. NCT00311766 tested Thymosin Beta-4 for epidermolysis bullosa and was terminated for lack of patient availability and drug expiration. Neither trial tested the TB-500 fragment.

No human trial of TB-500 itself has been identified. A retrospective case series (Lee & Padgett 2021, PMID 34324435) is sometimes cited in connection with TB-500, but its own text names the second peptide in its combination arm as “thymosin-beta-4 (TB4),” never TB-500 — that study is evidence for Thymosin Beta-4 in combination with BPC-157, not for TB-500.

Animal Evidence

Bock-Marquette et al. 2004 (Nature, PMID 15565145) reported Thymosin Beta-4 was cardioprotective after myocardial infarction in mice.

Biçer et al. 2026 (Jt Dis Relat Surg, PMID 42542926) is the one study located that names TB-500 specifically in its own methods (“synthetic thymosin beta-4 (TB-500),” 60 µg/kg/day): a rat Achilles-tendon-transection model (n=32) testing BPC-157 alone, TB-500 alone, and the combination. TB-500 alone produced the strongest biomechanical result of the three treatment arms; the combination did not confer additional benefit over TB-500 alone.

Evidence Level

TB-500: Animal Model (Biçer et al. 2026). Thymosin Beta-4: Human RCT for the pressure-ulcer indication (NCT00382174), though the trial found no benefit over placebo; Human Observational for epidermolysis bullosa (NCT00311766, terminated before a benefit could be assessed).

FAQ

Is TB-500 the same molecule as Thymosin Beta-4?

No. Esposito et al. 2012 (Drug Test Anal, PMID 22962027), an anti-doping laboratory's mass-spectrometry analysis of a commercial TB-500 product, identified it as the N-terminal acetylated 17-23 fragment of Thymosin Beta-4 (Ac-LKKTETQ) — 7 amino acids, not the 43-amino-acid full-length protein.

Do the RegeneRx human trials count as evidence for TB-500?

No. RegeneRx's Phase 2 trials (NCT00382174, pressure ulcers, completed with no benefit over placebo; NCT00311766, epidermolysis bullosa, terminated) tested native, full-length Thymosin Beta-4, not the TB-500 fragment. No human trial of TB-500 itself has been identified.

Is there any study that names TB-500 specifically?

Biçer et al. 2026 (Jt Dis Relat Surg, PMID 42542926) is an animal study — a rat Achilles-tendon model — whose own methods describe the compound administered as “synthetic thymosin beta-4 (TB-500)” at 60 µg/kg/day. This is the only study located that names TB-500 specifically; it did not confer additional benefit when combined with BPC-157 over either agent alone.

References

  1. 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, a product suspected to possess doping potential. Drug Test Anal. 2012;4(9):733-738. https://pubmed.ncbi.nlm.nih.gov/22962027/
  2. Bock-Marquette I, Saxena A, White MD, Dimaio JM, Srivastava D. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004;432(7016):466-472. https://pubmed.ncbi.nlm.nih.gov/15565145/
  3. Biçer O, Adanir O, Güleryüz Y, et al. Effects of BPC-157 and TB-500 on Achilles tendon healing in rats: A histopathological and biomechanical study. Jt Dis Relat Surg. 2026;37(3):822-837. https://pubmed.ncbi.nlm.nih.gov/42542926/
  4. Lee E, Padgett B. Intra-Articular Injection of BPC 157 for Multiple Types of Knee Pain. Altern Ther Health Med. 2021;27(4):8-13. https://pubmed.ncbi.nlm.nih.gov/34324435/
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