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TB-500 Script

TB-500 references: thymosin beta-4 and the FDA record

The papers behind the repair story, the fragment’s analytical identity and the official compounding record.

The muscle resultFollow the regulatory dates

The muscle paper belongs near the front

Spurney and colleagues’ dystrophin-deficient mouse experiment is my starting point. It increased regenerating muscle fibers without significant improvements in strength or systolic cardiac function. The rat wound study and mouse cardiac repair paper give the positive findings their own experimental settings. These studies tested full-length thymosin beta-4; human TB-500 treatment was outside their scope.

The Ho equine doping-control study is the important identity reference for the acetylated LKKTETQ fragment. It detects TB-500 and its metabolites in horse samples. Detection is a different claim from injury repair.

Human exposure data and the ClinicalTrials.gov question

A search for TB-500 human trials on ClinicalTrials.gov raises the molecule question before the efficacy question. The human paper here is Ruff and colleagues’ full-length thymosin beta-4 Phase 1 study in healthy volunteers; it reports tolerability and pharmacokinetics and leaves fragment efficacy untested. No completed controlled human trial of the TB-500 heptapeptide is established by this record.

For the FDA human exposure-data question, the safety-risk page names the LKKTETQ fragment and describes missing important safety information. I’m unconvinced when a parent-protein trial silently answers the fragment’s safety question. Full-length exposure and fragment exposure are different facts.

FDA sources have different jobs

The significant-safety-risks page describes the fragment’s safety concerns. On FDA’s page current as of April 22, 2026, the fragment appears in the nominated-but-withdrawn table, no longer in Category 2. The July advisory-committee calendar records the discussion, while the 503A bulk-substance page and compounding questions and answers explain the framework.

The legal-status account brings the dated facts together. The Sports Medicine review supplies the broader unapproved-peptide context. The complete reading list follows.

  1. Irobi E, et al. Structural basis of actin sequestration by thymosin-beta4: implications for WH2 proteins. EMBO J. 2004;23(18):3599-3608. ↗
  2. Bock-Marquette I, et al. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004;432(7016):466-472. ↗
  3. Malinda KM, et al. Thymosin beta4 accelerates wound healing. J Invest Dermatol. 1999;113(3):364-368. ↗
  4. Morris DC, et al. A dose-response study of thymosin β4 for the treatment of acute stroke. J Neurol Sci. 2014;345(1-2):61-67. ↗
  5. Goldstein AL, Hannappel E, Sosne G, Kleinman HK. Thymosin β4: a multi-functional regenerative peptide. Basic properties and clinical applications. Expert Opin Biol Ther. 2012;12(1):37-51. ↗
  6. Ruff D, et al. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin β4 in healthy volunteers. Ann N Y Acad Sci. 2010;1194:223-229. ↗
  7. Qiu P, et al. Thymosin beta4 promotes matrix metalloproteinase expression during wound repair. J Cell Physiol. 2007;212(2):548-558. ↗
  8. Sosne G, et al. Thymosin beta 4 suppression of corneal NFkappaB: a potential anti-inflammatory pathway. Exp Eye Res. 2007;84(4):663-669. ↗
  9. Stark C, et al. Cardioprotection by systemic dosing of thymosin beta four following ischemic myocardial injury. Front Pharmacol. 2013;4:149. ↗
  10. Mendias CL, Awan TM. Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance. Sports Med. 2026. ↗
  11. Lee Y, et al. Thymosin β4 Regulates Tissue Inflammatory Response in Mouse Nonalcoholic Fatty Liver Disease. J Inflamm Res. 2025;18:5959-5974. ↗
  12. Wei Y, et al. Inhaled exogenous thymosin beta 4 suppresses bleomycin-induced pulmonary fibrosis. J Pharm Pharmacol. 2024;76(12):1594-1605. ↗
  13. Chen Y, et al. Thymosin β4 released from functionalized self-assembling peptide activates cardiac cells and promotes cardiac repair. Theranostics. 2021;11(10):4974-4992. ↗
  14. Zhang Y, et al. Tβ4-exosome-loaded hemostatic and antibacterial hydrogel to improve vascularized wound repair. Mater Today Bio. 2025;32:101585. ↗
  15. Su Y, et al. Thymosin β4 promotes zebrafish Mauthner axon regeneration by facilitating actin dynamics. BMC Biol. 2024;22(1):238. ↗
  16. FDA. July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee. U.S. Food and Drug Administration advisory-committee calendar. Lists 'TB-500 (free base),' 'TB-500 acetate,' BPC-157, KPV, and MOTs-C as bulk drug substances being considered for inclusion on the 503A Bulks List (scheduled discussion, not a decision). ↗
  17. FDA. Certain Bulk Drug Substances for Use in Compounding That May Present Significant Safety Risks. U.S. Food and Drug Administration. Lists 'Thymosin beta-4, fragment (LKKTETQ), also known as TB-500' in Category 2 (effective with the September 29, 2023 update), citing potential immunogenicity for certain routes and a lack of important safety information. ↗
  18. FDA. Bulk Drug Substances Used in Compounding Under Section 503A of the FD&C Act. U.S. Food and Drug Administration. Definitions of the 503A/503B framework and Category 1 / Category 2; statement that substances nominated on or after January 7, 2025 are not placed into these categories. ↗
  19. McDermott Will & Emery. End of an Era: FDA Retires 2017 Interim Policies for Bulk Drug Lists. Legal analysis of the January 7, 2025 FDA action confirming that existing Category 1 substances retain enforcement discretion while Category 2 substances do not regain it even with updated nominations. ↗
  20. FDA. Compounding and the FDA: Questions and Answers (Section 503A patient-specific compounding and Section 503B outsourcing facilities). U.S. Food and Drug Administration. Basis for the lawful access pathway: licensed-prescriber evaluation and valid patient-specific prescription, dispensed by a 503A pharmacy or 503B outsourcing facility, using only eligible bulk substances. ↗
  21. Cha HJ, Jeong MJ, Kleinman HK. Role of thymosin beta4 in tumor metastasis and angiogenesis. J Natl Cancer Inst. 2003. ↗
  22. Zhang Y, et al.. Thymosin beta 4 is overexpressed in human pancreatic cancer cells and stimulates proinflammatory cytokine secretion and JNK activation. Cancer Biol Ther. 2008. ↗
  23. Ho EN, et al.. 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. J Chromatogr A. 2012. ↗
  24. Spurney CF, et al.. Evaluation of skeletal and cardiac muscle function after chronic administration of thymosin beta-4 in the dystrophin deficient mouse. PLoS One. 2010. ↗
  25. Delcourt V, et al.. TB500/TB1000 and SGF1000: A scientific approach for a better understanding of misbranded and adulterated drugs. Drug Test Anal. 2023. ↗