Educational reference, not medical advice. This page summarizes information from published research and regulatory filings for educational purposes. It is not a recommendation to use any compound and should not replace guidance from a licensed healthcare provider. Most peptides discussed here are not approved for the uses described.
What it is
TB-500 is the marketing name for a synthetic 7-amino-acid peptide corresponding to residues 17-23 of Thymosin Beta-4 (Tβ4). The fragment contains the actin-binding motif of the parent protein. Vendors and the published equine literature often use "TB-500" and "Thymosin Beta-4" interchangeably, but they are distinct molecules: TB4 is the full 43-amino-acid protein found in nearly every human tissue; TB-500 is just the active fragment.
History and research stage
Thymosin Beta-4 was isolated from calf thymus by the Goldstein laboratory in the 1980s and characterized as the major actin-sequestering protein in mammalian cells. Research interest expanded through the 1990s and 2000s as TB4 was shown to participate in wound healing, angiogenesis, and cardiac repair.
The shorter TB-500 fragment entered the market through veterinary use in performance horses, where it was marketed for injury rehabilitation. From there it migrated into human research peptide channels. The full-length TB4 molecule has been studied in human clinical trials by RegeneRx Biopharmaceuticals — including the RGN-259 program for corneal wounds and dry eye, which reached Phase III — but the 7-residue TB-500 fragment itself has not been tested in registered human trials.
Regulatory status
No regulatory approval exists for TB-500 in any jurisdiction. The World Anti-Doping Agency added TB-500 to its prohibited list in 2011 (S2 — peptide hormones, growth factors, and related substances), and high-profile bans of professional athletes followed in Australian rugby and racing. In the United States it is sold only through research chemical suppliers and is not on any approved compounding list.
Full-length Tβ4 (RGN-259) has progressed through Phase III for dry eye and remains in development; this is a different molecule than what is sold as TB-500.
How researchers describe its action
The published mechanism papers describe Tβ4 as an actin monomer sequester that promotes cell migration into wound beds, accelerates revascularization through VEGF and angiopoietin signaling, and reduces inflammation through downregulation of NF-κB. The TB-500 fragment retains the actin-binding sequence and is presumed to share these effects, though direct mechanism studies on the fragment alone are sparse compared with the parent protein.
Half-life and dosing intervals
Published estimates for TB-500 give a circulating half-life of approximately 1.5 to 3 hours after subcutaneous injection. The longer effective duration in animal studies has been attributed to its rapid tissue distribution and binding to actin within target cells.
In veterinary protocols and the human research peptide market, dosing schedules described observationally typically involve a loading phase of 4–10 mg per week (divided into two injections) for the first 4–6 weeks, followed by a maintenance phase of 2–6 mg per month. These figures are not derived from controlled human trials and should not be interpreted as established therapeutic doses.
Reconstitution example
TB-500 vials are typically 2 mg, 5 mg, or 10 mg lyophilized powder. A 10 mg vial reconstituted with 2 mL of bacteriostatic water yields 5 mg/mL. On a 1 mL U-100 insulin syringe, 0.2 mL (20 units) delivers 1 mg.
What to know
- Limited human data. The fragment-specific clinical evidence is essentially absent. Most rodent and equine work uses full-length Tβ4.
- WADA-banned. Athletes subject to sport drug testing should not use TB-500.
- Storage. Refrigerate lyophilized vials. Once reconstituted, refrigerate and use within 4 weeks per stability data published for TB4.
- Reported side effects in user reports include lethargy and mild flu-like symptoms during the first weeks of high-dose protocols; serious adverse events have not been documented in peer-reviewed literature.
Sources
- 1.Goldstein AL et al. (2012). Thymosin β4: a multifunctional regenerative peptide. Expert Opinion on Biological Therapy.
- 2.Crockford D (2007). Thymosin beta4 — a novel cardiovascular therapeutic. Annals of the New York Academy of Sciences.
- 3.WADA 2024 Prohibited List — peptide hormones (S2).
- 4.Sosne G et al. (2010). Thymosin beta 4 promotes corneal wound healing. Annals of the New York Academy of Sciences.