Frequently asked questions
TB-500: the questions people actually ask, answered from the record
Each answer leads with the finding and cites it. Where the honest answer is "no human data," the answer says so.
What is TB-500?
TB-500 is the synthetic N-acetylated heptapeptide Ac-LKKTETQ, corresponding to residues 17–23 — the actin-binding motif — of the 43-amino-acid protein thymosin beta-4 [1]. It is a research and veterinary-context substance with no approved human indication. The parent protein is endogenous; the fragment is a synthetic construct.
What does TB-500 stand for?
"TB" references thymosin beta-4 (Tβ4), the parent protein; "TB-500" is the commercial and veterinary research designation for its synthetic Ac-LKKTETQ actin-binding fragment [1]. The number is a product label, not a chemical descriptor. The same fragment is also seen under designations such as TB1000.
What is TB-500 used for in research?
In animal and cell models, thymosin beta-4 and its actin-binding region are studied for wound healing, muscle and ligament repair, angiogenesis, and cardiac and neurological recovery [5][7]. The efficacy of the isolated seven-mer is unproven in controlled human trials [4]. Most studied outcomes are properties of the parent protein.
How does TB-500 work?
TB-500 carries the actin-binding LKKTETQ motif of thymosin beta-4, the body's main G-actin sequestering peptide [1]. Full-length thymosin beta-4 binds monomeric actin one-to-one to regulate cytoskeletal dynamics, cell migration, angiogenesis, and anti-inflammatory signaling [5]. Whether the isolated seven-mer reproduces these at research doses is not established in humans.
Is TB-500 a steroid?
No. TB-500 is a peptide fragment — the seven-amino-acid Ac-LKKTETQ sequence from thymosin beta-4 — not a steroid [1]. Steroids are lipid molecules built on a four-ring carbon skeleton and act through nuclear hormone receptors; TB-500 is a short chain of amino acids whose studied mechanism is actin binding. The two are unrelated chemical classes.
What are the side effects of TB-500?
Rigorous human safety data for the TB-500 fragment are scarce. The most-cited concern is the tumor/angiogenesis signal associated with thymosin beta-4 [12]. Full-length thymosin beta-4 was well tolerated to 1260 mg IV in a Phase 1 study, but that does not characterize the fragment in real-world research use [4]. Material-quality and purity issues add further uncertainty.
Does TB-500 cause cancer or promote tumor growth?
Thymosin beta-4 is overexpressed in several cancers and implicated in metastasis and tumor angiogenesis; the same pro-migratory, pro-angiogenic properties that aid repair could theoretically support tumor progression [12]. This is a recognized safety signal, not a demonstrated human risk for the fragment. It is the principal theoretical concern in the literature, and it is reported here as a signal, not a verdict.
Does TB-500 increase hair growth?
Thymosin beta-4 at nanomolar concentrations stimulated hair growth in rats and mice by activating hair-follicle bulge stem cells [5]. This is an animal finding for the full-length protein and is not established for the TB-500 fragment in humans [4]. The mechanism is consistent with the protein's broader cell-migration and stem-cell activity.
Is TB-500 safe? What the literature shows
There is no controlled human safety dataset for the TB-500 fragment itself, so "safe" cannot be confirmed by a fragment-specific trial [4]. The adjacent evidence is mixed: the parent protein was well tolerated to 1260 mg IV in Phase 1 [4]; a null muscle-strength result appeared in mdx mice [8]; and the tumor/angiogenesis signal stands [12]. Confident about the structure and animal data, candid about the human gap.
Are there any human clinical trials on TB-500?
No completed controlled clinical trials of the TB-500 fragment exist for any indication [4]. Human data are limited to full-length thymosin beta-4 — a Phase 1 IV safety study (well tolerated to 1260 mg) [4] and topical ophthalmic trials. An injectable thymosin beta-4 acute-stroke trial was registered and then withdrawn [10].
Is TB-500 FDA approved?
No. TB-500 has no FDA-approved therapeutic indication [16]. It is a research and veterinary-context substance, and human data exist only for full-length thymosin beta-4, not the fragment [4]. FDA placed the LKKTETQ fragment in 503A Category 2 [16]. Full detail is on the TB-500 legal status and 503A access page.
Is TB-500 legal?
TB-500 has no FDA-approved human indication, is sold by research suppliers for laboratory use only, is WADA-prohibited in sport, and is classified as a prescription medicine in some jurisdictions [16][4]. FDA placed it in 503A Category 2, so it is not eligible for routine 503A compounding while that status stands [16][17]. This is general information, not legal advice.