Gathering the record
Relay is organizing the evidence and source boundaries.
N-acetylated thymosin beta-4 heptapeptide fragment
TB-500 is a synthetic seven-amino-acid fragment of thymosin beta-4. It is not the full 43-amino-acid molecule. No human TB-500 studies were located, and human thymosin beta-4 findings should not be transferred to this fragment.
60-Second Overview
Start with what it is, why it matters, what research has shown, and what remains unknown. The science follows after the orientation.
Start here. These four answers explain why the compound matters before the page introduces the deeper science.
TB-500 is a synthetic seven-amino-acid fragment derived from part of thymosin beta-4. It is not the full 43-amino-acid thymosin beta-4 molecule used in separate human research.
Interest comes from repair biology associated with the parent peptide and from laboratory work on how the smaller fragment is broken down. The key question is whether the fragment itself has any meaningful human effect.
Laboratory and animal studies describe TB-500 metabolism and detection. In one fibroblast experiment, the parent fragment did not improve scratch-wound closure at the tested concentration, although a shorter metabolite showed activity. No human TB-500 administration study was located.
Human pharmacokinetics, effectiveness, acute and repeated-use safety, immunogenicity, product identity, and any healing outcome remain unknown. Findings from full-length thymosin beta-4 cannot be transferred to TB-500.
The research depth, routes, studies, and primary sources below explain how Relay knows—and where the evidence stops.
Research context
Published research has investigated this compound using the following study designs.
These records explain what researchers did. They are not instructions, recommendations, or a transferable protocol.
Published research investigated TB-500 in human-derived laboratory systems, cultured fibroblasts, and rats to characterize breakdown products and experimental wound-closure signals.
Reported study administration—not a recommendation.
Research at a glance
Evidence depth, confidence, and route context explain how Relay knows—not what anyone should do.
The traceable evidence consists of analytical, cell, rat, and equine work on the seven-amino-acid fragment.
Research depth describes how large and mature the overall record is. It does not tell you whether the results were positive.
No human exposure, pharmacokinetic, safety, or efficacy study of verified TB-500 was located.
Confidence describes how reliable and consistent the conclusions are. It can be high for one outcome and low for another.
The strongest evidence type shows what the best-supported conclusions are actually based on.
Human findings are more directly relevant than animal or laboratory results, but they still apply only to the populations and outcomes studied.
Route-specific record
These are exposures used in cited research for a specific route and population—not an instruction for an individual.
Half-life describes how long it takes the measured amount in the body to fall by half. It is not a dosing recommendation.
Evidence can change by administration method. Findings from one route should not automatically be applied to another.
Evidence boundary: No verified human administration, pharmacokinetic, efficacy, or safety study was located. A laboratory metabolite signal does not establish benefit from the parent fragment, and full-length thymosin beta-4 is a different identity. Amounts shown describe cited research exposure—not a dosage recommendation.
Detailed evidence
Start with the strongest supported conclusion and its main uncertainty. Claim-level records below show how the evidence changes by question, population, route, formulation, and study design.
None located. FDA found no clinical study or human exposure data for TB-500 free base or acetate by any route.
This is the strongest supported conclusion in the current human evidence—not a summary of every claim made about the compound.
Whether TB-500 has any clinically meaningful human effect, how it behaves in people, repeated-exposure safety, and whether a labeled material is actually the stated free base or acetate.
Keeping the main uncertainty visible prevents an early or promising finding from looking more settled than it is.
Questions people bring to the evidence
Research questions—not promises of benefit.
FDA identifies TB-500 free base as Ac-LKKTETQ, corresponding to residues 17-23 of the 43-amino-acid thymosin beta-4 molecule.
FDA searched the medical literature and trial registry and found no TB-500 administration in humans by any route.
FDA explicitly distinguishes the 43-amino-acid molecule from the seven-amino-acid TB-500 fragment.
The 2024 laboratory study found activity for one shorter metabolite, not for parent TB-500 at the tested concentration.
FDA found mismatched names, salts, formulas, identifiers, and certificates.
The July 23 committee recommendation favored inclusion despite FDA's negative review. FDA makes the final decision, and compounded drugs are not FDA approved.
Mechanisms
TB-500 free base is N-acetyl-LKKTETQ, corresponding to thymosin beta-4 residues 17-23. The acetate salt is a distinct bulk drug substance. Located evidence covers analytical identity, animal and in-vitro metabolism, and a fibroblast scratch-wound assay. FDA found no human exposure, PK/PD, safety, or efficacy studies by any route.
A plausible mechanism can explain why a study was attempted. It does not prove that the compound improves a human outcome.
Studies
Study arms are reported for transparency. They describe what researchers did in a defined record and do not transfer across identities, routes, formulations, or populations.
A later trial phase can ask a more mature question, but it does not guarantee a positive result, regulatory approval, or relevance outside the studied population.
TB-500 metabolism in human-derived in-vitro systems and rats, with fibroblast scratch-wound assays
Human serum and microsomal systems, cultured fibroblasts, and rats
TB-500 was broken down into shorter acetylated peptides. Parent TB-500 did not improve fibroblast scratch-wound closure at the tested concentration; one shorter metabolite, Ac-LKKTE, showed activity.
Study administration: TB-500 free base and synthesized metabolites under laboratory protocols
Limitations: Laboratory and rat findings do not demonstrate healing, effectiveness, pharmacokinetics, or safety in people. A metabolite result cannot be assigned to the parent peptide without human evidence.
Liquid chromatography-mass spectrometry identification after research administration in horses
Horses
The parent peptide and multiple C-terminally shortened metabolites were detected in equine plasma and urine.
Study administration: Protocol-defined subcutaneous TB-500 free base administration
Limitations: Animal detection and metabolism study, not a wound-healing or efficacy study. It cannot establish a human dose, route, benefit, or safety profile.
Safety snapshot
No human TB-500 exposure, pharmacokinetic, safety, or efficacy study was located.
No direct evidenceNo reported case does not mean proven safety. Human benefits, adverse effects, and repeated-exposure risks remain unknown.
Open sourceThe current record does not support a reliable common-versus-uncommon frequency split.
Evidence boundaryUnder-detected or under-reported events must not be described as rare.
No source-qualified compound-specific warning or contraindication is encoded in the current record.
Evidence boundaryNot FDA approved. On July 23, 2026, PCAC voted 8-6 with one abstention to recommend adding TB-500 free base and acetate to the 503A Bulks List despite FDA's negative recommendation. The vote is nonbinding and final FDA action was not located by July 25. WADA prohibits thymosin beta-4 and derivatives including TB-500. Whether TB-500 has any clinically meaningful human effect, how it behaves in people, repeated-exposure safety, and whether a labeled material is actually the stated free base or acetate.
The current record does not identify a reliable compound-specific pattern of events that caused study discontinuation.
Evidence boundaryThis is an evidence gap, not proof that discontinuations did not occur.
No compound-specific patient-facing urgent-action threshold is established in the current Relay record.
Evidence boundaryRelay does not infer emergency guidance from study discontinuations, mechanism, or incomplete adverse-event reporting.
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2024-03-15 · PMID 38382158 · DOI 10.1016/j.jchromb.2024.124033
2012-11-23 · PMID 23084823 · DOI 10.1016/j.chroma.2012.09.043
2012-09-07 · PMID 22962027 · DOI 10.1002/dta.1402