VialOwlLibrary / Repair and recovery
TB-500
Also known as Thymosin beta-4 fragment, Ac-LKKTETQ
Animal studies only
Synthetic fragment of thymosin beta-4 containing its actin binding region. Studied in animals for wound and tissue healing; FDA noted no human exposure data for this form.
Not an approved medicine. TB-500 is not an approved medicine for this use in Australia or the United States. This page summarises published research for information only. It is not a recommendation to use TB-500, and VialOwl does not sell or supply it.
Background
Synthetic product based on the short actin binding region of thymosin beta-4 (amino acids 17 to 23, acetylated: Ac-LKKTETQ). It emerged in horse racing and grey market circles, and anti doping laboratories identified its contents in 2012.
How it is thought to work
Thought to copy the part of thymosin beta-4 that binds actin, a protein cells use to move, which in animal studies helps wound healing and new blood vessel growth. Whether the short fragment behaves like the full protein in people is unknown.
What is claimed, and the evidence
| Claim | Evidence | Notes |
|---|---|---|
| Speeds healing of muscle, tendon and ligament injuries | Animal studies only | Based on animal studies of full length thymosin beta-4; FDA found no human exposure data for the fragment. |
| Reduces inflammation and improves flexibility | No published evidence | Common marketing claim with no published human evidence. |
| Improves hair growth or heart repair | Animal studies only | Extrapolated from animal work on full length thymosin beta-4. |
| Enhances athletic or racing performance | No published evidence | Its detection in horse doping tests reflects misuse, not proven benefit. |
Side effects
| Effect | How often | Notes |
|---|---|---|
| No published human safety data Serious | Frequency unknown | FDA states it has not identified any human exposure data for this fragment. |
| Immune reactions to aggregates or impurities Serious | Frequency unknown | FDA flags possible immunogenicity from aggregation and peptide related impurities. |
| Injection site infection or reactions Serious | Frequency unknown | TGA warns injected unapproved peptides can cause infection and tissue damage. |
Warnings
- No human safety or efficacy data exist; all claimed benefits are extrapolated from animal studies of a different, full length molecule.
- In Australia it is Schedule 4 with Appendix D possession controls; the TGA names it as an unapproved peptide product.
- Banned in sport and horse racing.
- Unapproved products are not made to medicine standards and may be contaminated, underdosed, overdosed or contain a different substance from the label; the TGA warns that injected unapproved peptides carry risks including contamination, infection and local tissue damage.
Regulatory status
- Australia
- Not included on the ARTG (unapproved). Schedule 4 (Prescription Only Medicine) in the Poisons Standard, also listed in Appendix D clause 5 (possession without authority is illegal). TGA names it as an example of an unapproved peptide product.
- United States
- Not FDA approved. Nomination withdrawn and removed from 503A Category 2 in April 2026. In July 2026 an FDA advisory committee voted 8 to 6 to recommend it for the 503A bulks list; FDA has not finalised this.
Sources
- Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500
- Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance
- FDA: Certain bulk drug substances for use in compounding that may present significant safety risks
- TGA: Understanding your responsibilities when importing, compounding and supplying unapproved peptide products
- Poisons Standard June 2026 (Federal Register of Legislation)
Also in Repair and recovery
From the VialOwl library, reviewed 26 September 2026. For education and general information. It is not medical advice and not a recommendation to use TB-500.