# TB-500 FAQ: Mechanism, Safety, Recovery, and Regulatory Questions

> TB-500 questions answered from the cited literature: what it is, how it works, side effects, whether it is a steroid, recovery evidence, half-life, and FDA and WADA status.

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](/legal-status) 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.

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A clear-eyed digest of the TB-500 and thymosin beta-4 record, read by glow intensity — the established findings bright, the human-data gaps left dim and labeled, with no clinic behind the aurora and nothing here dispensed.