A graded reading of the evidence. It recommends nothing and gives no dosing or reconstitution detail; the job here is to separate what was tested from what is sold.

01 Identity — and a critical distinction

Common name	TB-500
Marketed as	"Synthetic thymosin β4" / a synthetic active fragment of Tβ4
Parent protein	Thymosin β4 (Tβ4) — naturally occurring 43-amino-acid actin-sequestering peptide
Relationship	TB-500 is a synthetic active region of Tβ4 — not identical to the full-length protein
Tβ4 reference	PubChem CID 16133418; MW ≈ 4,982 Da; N-terminally acetylated

The single most important fact on this page: the human clinical-trial data usually cited for "TB-500" belong to full-length thymosin β4 (Tβ4), not to TB-500 as sold. TB-500 is a synthetic fragment; the two are related but distinct, and the marketed injectable has not itself been through the clinical pipeline. Vendors routinely conflate them. This monograph keeps them separate; the parent protein's full clinical record is in the Thymosin β4 monograph.

02 Regulatory status

Neither TB-500 nor thymosin β4 is approved for any indication by the FDA, EMA, or MHRA. The furthest-developed Tβ4 product, RGN-259 (0.1% Tβ4 ophthalmic solution), completed late-stage ophthalmic trials and holds orphan-drug designation for neurotrophic keratopathy, but has no marketing approval.

WADA prohibits TB-500 / Tβ4 (class S2). In the US both are handled through compounding channels and subject to the FDA's compounding-substance review. Otherwise sold as a "research chemical." Confirm specifics against FDA and WADA documents.

03 Mechanism of action

Thymosin β4 is the major intracellular G-actin-sequestering molecule, regulating the actin polymerisation behind cell migration. Reported downstream effects (mostly preclinical) include cell migration, angiogenesis, anti-inflammatory and anti-fibrotic signalling, and, in a mouse study (Bock-Marquette et al., Nature 2004), integrin-linked-kinase activation with cardioprotection after experimental infarction.

TB-500 is held to retain activity because it preserves the active core of Tβ4; some sources attribute the fragment's activity to a metabolite. Well-characterised for the parent protein; for the marketed fragment specifically it is more assumed than independently established.

04 Pharmacokinetics / pharmacodynamics

Human PK for injected TB-500 are uncharacterised. For the parent protein, a Phase 1 study of IV Tβ4 in 40 healthy volunteers reported no dose-limiting toxicities — establishing short-term IV tolerability of Tβ4, not the long-term safety of subcutaneous TB-500.

05 Evidence by endpoint

Endpoints split sharply by which molecule and which route is meant.

5.1 — Musculoskeletal injury / recovery (injected TB-500) — the popular use

The use TB-500 is marketed for — accelerating recovery from muscle, tendon, and ligament injury via injection — has no human trials. Supporting data are preclinical and anecdotal. The human evidence cited in marketing is for a different molecule in different indications (below).

Preclinical only — no human trials

5.2 — The human evidence (Tβ4) — see the dedicated monograph

What human trials exist belong to full-length thymosin β4, not to injected TB-500, and they sit in local indications: topical ophthalmic (dry eye Phase 2 positive; Phase 3 mixed; neurotrophic keratopathy promising), topical dermal wound healing (Phase 2), and an early cardiac pilot. To avoid duplicating that record here, it is covered in full — with grades and citations — in the Thymosin β4 monograph. The point for this page is only that none of it is evidence for the injected fragment sold as TB-500.

Tβ4 evidence summarised in the TB4 monograph

5.3 — Mechanism (actin sequestration, angiogenesis, anti-fibrosis)

Well-characterised for Tβ4 in cells and animals.

Mechanistic / preclinical

06 Safety and adverse events

For injected TB-500 there is no human safety data. Safety information that exists is for Tβ4: a Phase 1 IV study in 40 healthy volunteers reported short-term tolerability, and topical ophthalmic/dermal trials reported acceptable safety. None of this characterises the long-term safety of subcutaneous TB-500.

Both are prohibited in sport (WADA S2). Product identity, purity, and sterility vary in research-chemical material and are unverifiable without independent testing. No long-term human safety data exist for TB-500. A theoretical note: by promoting cell migration and angiogenesis, this class is theoretically relevant to tumour biology — neither demonstrated nor excluded in humans, flagged as an open question, not a finding.

07 Evidence summary

Endpoint (molecule / route)	Grade
Injury recovery — TB-500, injected (marketed use)	Preclinical — no human trials
Tβ4 (parent protein) — ophthalmic / dermal / cardiac	graded in the TB4 monograph
Long-term safety — injected TB-500	No data

08 References

Bock-Marquette I, et al. Thymosin β4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004;432:466–472.
Malinda KM, et al. Thymosin β4 accelerates wound healing. J Invest Dermatol. 1999.
Sosne G, et al. Thymosin β4 significantly improves signs and symptoms of severe dry eye in a Phase 2 randomized trial. Cornea. 2015;34(5).PMID 26056426
Guarnera G, et al. Topical thymosin β4 for chronic wounds — double-blind placebo-controlled Phase 2. 2010.NCT00382174 · confirm citation
Ruff D, et al. Phase 1 IV thymosin β4 safety study (40 healthy volunteers). 2010.Confirm citation
RegeneRx — pilot trial of Tβ4-treated EPCs in STEMI patients (2016); RGN-352 development.Company / clinical source
WADA — Prohibited List, class S2.Confirm current listing