What is Thymosin β4 (Tβ4)?

An endogenous actin-sequestering peptide involved in wound healing. Structurally it is Actin-binding peptide (43 aa).

How strong is the evidence for Tβ4?

PeptideHormone grades Tβ4 at the "Established" evidence tier — its mechanism and core effects are settled across the peer-reviewed literature. It is catalogued as an endogenous signal the body produces itself, and the tier is an editorial judgment about the public literature that can change as the science does.

What is the half-life of Tβ4?

The reported circulating half-life of Tβ4 is Poorly characterized in humans.

Is Tβ4 FDA-approved?

No — as of September 2026, Tβ4 is sold outside the approved-drug system as research-use-only material, with no FDA approval for human use. No approved product; RGN-259 (Tβ4 eye drops) has completed Phase 3 trials in dry eye without approval. Status is US-centric and can change; check the FDA record for the current position.

Thymosin β4Tβ4

An endogenous actin-sequestering peptide involved in wound healing.

EndogenousEstablishedUnapproved Compare lineage

An actin-binding protein that turns out to matter in healing — a reminder that structural molecules can carry signals too.

Identity

Class: Actin-binding peptide (43 aa)
Source: Widespread; abundant intracellularly
Receptor: No classical receptor; sequesters monomeric (G-)actin

Key properties

Evidence floorCommunityREF1COMM1

Molecular weight

~4,963.4 Da

REF

Half-life (native)

Poorly characterized in humans

COMMHalf-life is poorly characterized in humans. The figure is indicative of order-of-magnitude, not an established value.

Approximate values for the native hormone; engineered analogs are often deliberately larger and far longer-acting. Each figure carries its own provenance tier, and the floor is the weakest of them - the Standard.

Mechanism

Thymosin β4 is the major intracellular store of monomeric actin, buffering the actin available for cytoskeletal remodeling. Through effects on cell migration, angiogenesis, and inflammation it supports tissue repair, which underlies its study in wound healing and the existence of fragment-based research compounds.

Reference notes

Tβ4 works by binding monomeric actin, not by activating a surface receptor.
Its repair effects come from modulating cell migration, angiogenesis, and inflammation.
It is the endogenous molecule that the research compound TB-500 is derived from — they are not identical.

Regulatory status

United States · reviewed September 2026

UnapprovedTβ4 is sold outside the approved-drug system as research-use-only material, with no FDA approval for human use.

Basis: No approved product; RGN-259 (Tβ4 eye drops) has completed Phase 3 trials in dry eye without approval.

Status describes the molecule as a drug substance under US law and is an editorial reading of the public record — approvals, trial registrations, and the FDA 503A bulk-substances list. It is not legal advice and it changes; the review date above is the last time the table was checked. Other jurisdictions are noted only where they differ materially.

Common questions

What is Thymosin β4 (Tβ4)?: An endogenous actin-sequestering peptide involved in wound healing. Structurally it is Actin-binding peptide (43 aa).
How does Tβ4 work?: Thymosin β4 is the major intracellular store of monomeric actin, buffering the actin available for cytoskeletal remodeling. Through effects on cell migration, angiogenesis, and inflammation it supports tissue repair, which underlies its study in wound healing and the existence of fragment-based research compounds.
How strong is the evidence for Tβ4?: PeptideHormone grades Tβ4 at the "Established" evidence tier — its mechanism and core effects are settled across the peer-reviewed literature. It is catalogued as an endogenous signal the body produces itself, and the tier is an editorial judgment about the public literature that can change as the science does.
What is the half-life of Tβ4?: The reported circulating half-life of Tβ4 is Poorly characterized in humans.
Is Tβ4 FDA-approved?: No — as of September 2026, Tβ4 is sold outside the approved-drug system as research-use-only material, with no FDA approval for human use. No approved product; RGN-259 (Tβ4 eye drops) has completed Phase 3 trials in dry eye without approval. Status is US-centric and can change; check the FDA record for the current position.

In the literature

Live registry counts · retrieved 2026-09-15

Registered trialsREF

Ph 12
Ph 23
Ph 30
Ph 40

Open on ClinicalTrials.gov

Searched as Thymosin β4, thymosin beta4, thymosin beta-4. Counts are search hits from the primary registries, not a curated set and not a grade – a measure of how much work exists on Tβ4, not how it turned out.

Selected literature

Curated peer-reviewed reviews, sourced from PubMed. Selected for relevance, not exhaustive — open any entry on PubMed for the full record and its primary citations.

1.beta-Thymosins · Annals of the New York Academy of Sciences, 2007 · PMID 17468232
2.Thymosin β(4) and β(10) Expression in Human Organs during Development: A Review · Cells, 2024 · PMID 38994967

External references

Tβ4 in the public knowledge graph — the same entity resolved across the authoritative chemistry and protein databases.