TB-500 is the Ac-LKKTETQ fragment of thymosin beta-4, read against the research that exists.

What TB-500 is, in one readout

TB-500 is the synthetic, N-acetylated heptapeptide Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln — Ac-LKKTETQ, molecular weight 889.02 Da, formula C38H68N10O14. It corresponds to residues 17-23 of thymosin beta-4 (Tβ4, gene TMSB4X), the 43-amino-acid protein that is the body's principal actin-sequestering peptide. That short stretch is the conserved actin-binding motif of the beta-thymosins, which is why the fragment was carved out and named in the first place.

The single most important fact about TB-500 is a labeling fact, not a biology fact. In commerce and in the anti-doping literature, "TB-500" denotes the ~889 Da heptapeptide. But the overwhelming majority of efficacy research — wound healing, cardiac repair, angiogenesis, neuroprotection — was run on full-length recombinant or synthetic thymosin beta-4 (~4963 Da), not the 7-mer ^[5]. Whether the isolated fragment reproduces the parent protein's effects at the doses used in peptide research has not been established in controlled human trials ^[5]. This site flags that distinction on every finding it carries.

TB-500 has no FDA-approved therapeutic indication and is sold by research suppliers for laboratory use only. It is prohibited in sport by the World Anti-Doping Agency, and FDA has placed it in a flagged compounding category — covered in full on the TB-500 legal status and FDA 503A category page. What follows is the evidence, tagged by state: what the literature confirms, what is preclinical only, where there is no human data, and where there is a genuine tumor and angiogenesis safety signal. For the structural detail of how the actin-binding mechanism works, start with the research page.

TB-500 as a Peptide: the Ac-LKKTETQ Fragment of Thymosin Beta-4

As a peptide, the TB-500 sequence is short, acetylated, and defined entirely by its actin-binding job. The LKKTETQ motif is a WH2-type actin-interacting region — the same class of short motif that monomer-sequestering and filament-assembly proteins use to grip actin ^[1]. X-ray crystallography of a gelsolin-domain-1–thymosin beta-4 hybrid bound to actin (resolved to 2 Å) established that thymosin beta-4 forms a 1:1 complex with globular (G-) actin and holds the monomer by capping both of its ends, preventing it from polymerizing ^[1]. That structure is the mechanistic anchor for everything downstream.

Being a peptide, not a small molecule, shapes the practical picture. TB-500 is supplied as a lyophilized powder, reconstituted in sterile or bacteriostatic water, and kept refrigerated. As a short acetylated chain it is more chemically robust than the full-length protein, but it is still subject to proteolysis and freeze-thaw degradation, and the identity and purity of research-grade material — including whether a vial actually contains the fragment versus the full-length protein — is a recurring concern in unregulated supply ^[5]. The 7-mer also does not generate Ac-SDKP, the separate anti-fibrotic, angiogenic N-terminal cleavage product of full-length thymosin beta-4, because that product comes from the opposite end of the parent protein ^[5].

Thymosin Beta-4: the Parent Protein Behind Most TB-500 Research

Thymosin beta-4 is a ubiquitous 43-residue peptide present in nearly every human cell and released by platelets and macrophages at sites of injury ^[5]. It is the body's major intracellular G-actin sequestering molecule: it binds monomeric actin and buffers an unpolymerized reserve, regulating cytoskeletal dynamics, cell migration, and motility ^[1][5]. In injury models it is associated with accelerated cell migration, angiogenesis, anti-inflammatory and anti-apoptotic signaling, reduced scar formation, and recruitment of progenitor cells — the basis on which it was carried into clinical trials for dermal wounds, corneal injury, and heart and CNS repair ^[5].

The reason this matters for a TB-500 reader is direct. When a TB-500 product points to "the research," that research is, in most cases, the thymosin beta-4 literature summarized above. The fragment carries the actin-binding core of that protein, but a core is not the whole molecule, and the studies that produced the headline numbers used the whole molecule ^[5]. Read every TB-500 claim with that substitution in mind — the deeper treatment is on the research on thymosin beta-4.

What the human record actually shows

There are no completed controlled clinical trials of the TB-500 heptapeptide for any indication ^[5]. The human data that exist are for full-length synthetic thymosin beta-4. In a randomized, placebo-controlled Phase 1 study, intravenous thymosin beta-4 was given to 40 healthy volunteers — four cohorts of 10, a single dose then daily for 14 days at 42, 140, 420, or 1260 mg — and was well tolerated, with only infrequent mild-to-moderate adverse events, no dose-limiting toxicities, and no serious adverse events; pharmacokinetics were dose-proportional ^[6]. That is a genuine tolerability result, and it is a result for the parent protein given intravenously, not for the fragment.

Against that sits an honest safety signal. Thymosin beta-4 is overexpressed in several cancers and is implicated in tumor metastasis and angiogenesis ^[7][8]; the same pro-migratory, pro-angiogenic properties that aid repair could theoretically support tumor progression ^[7]. That is the lens this site leads with — the full treatment is on the TB-500 side effects page, and the regulatory picture is on the TB-500 legal status and FDA 503A category page. For quick answers, see the frequently asked questions about TB-500.

What TB-500 (and thymosin beta-4) has been studied for

Across animal and in-vitro work, thymosin beta-4 and its actin-binding region have been examined for wound healing, tissue and cell migration, angiogenesis, cardiac and neurological repair, and hair-follicle activation ^[5]. The strongest single readout is dermal: in a rat full-thickness wound model, topical or intraperitoneal thymosin beta-4 increased re-epithelialization by 42% at 4 days and up to 61% at 7 days versus saline, with greater wound contraction, collagen deposition, and angiogenesis; as little as 10 pg stimulated keratinocyte migration two- to three-fold ^[3].

The honest counterweight is just as important. In dystrophin-deficient mdx mice given 150 µg thymosin beta-4 intraperitoneally twice weekly for 6 months, the number of regenerating skeletal-muscle fibers rose significantly — but muscle strength, systolic cardiac function, and fibrosis did not improve ^[9]. More regenerating fibers without a functional gain is a result that any recovery-minded reader should sit with. Each of these findings, with its species and its source molecule tagged, is laid out on the research page.