# Thymosin Beta-4

> Evidence tier A — Controlled human trials · Repair · reviewed 2026-11-08
> Source page: https://peptidemeta.com/p/thymosin-beta-4/

Also known as: Tβ4, TMSB4X, RGN-259, RGN-137, Timbetasin

## Quick answers

**What is Thymosin Beta-4?**

The full-length naturally occurring protein from which TB-500 is derived.

**How strong is the evidence for Thymosin Beta-4?**

Tier A (controlled human trials) on the peptidemeta evidence scale. Randomized, placebo-controlled phase 2/3 trials have been run in humans (RGN-259 eye drops for dry eye and neurotrophic keratopathy; RGN-137 for chronic wounds); not approved.

**Is Thymosin Beta-4 FDA-approved?**

No. Thymosin Beta-4 is not approved by the FDA for any use.

**Is Thymosin Beta-4 banned in sport?**

Yes. Thymosin Beta-4 is prohibited in sport by the World Anti-Doping Agency under S2 (peptide hormones, growth factors, related substances and mimetics).

**How does Thymosin Beta-4 work?**

Thymosin beta-4 is a 43-amino-acid actin-sequestering protein that regulates cell motility by modulating actin polymerization. It promotes tissue repair through activation of integrin-linked kinase (ILK) and Akt survival pathways, while also suppressing inflammatory cytokines and promoting stem cell recruitment.

**What is known about the safety of Thymosin Beta-4?**

Phase II clinical trial data suggest acceptable safety. Naturally occurring in most human tissues.

## Key facts

- **Evidence tier:** A (Controlled human trials)
- **FDA:** not approved
- **WADA:** prohibited (S2)
- **Peptide:** yes
- **Discovered:** 1981 — Isolated from calf thymus (thymosin fraction 5) by Goldstein and colleagues.
- **Routes studied:** Subcutaneous, Intramuscular

## Overview

The full-length naturally occurring protein from which TB-500 is derived. It plays a critical role in cell migration, wound healing, and anti-inflammatory processes throughout the body.

## Mechanism

Thymosin beta-4 is a 43-amino-acid actin-sequestering protein that regulates cell motility by modulating actin polymerization. It promotes tissue repair through activation of integrin-linked kinase (ILK) and Akt survival pathways, while also suppressing inflammatory cytokines and promoting stem cell recruitment.

## Effects reported in research

_Reported outcomes, not promises; see the evidence tier._

- Comprehensive tissue regeneration
- Anti-inflammatory signaling
- Cardiac tissue protection
- Stem cell differentiation support

## Safety & unknowns

Phase II clinical trial data suggest acceptable safety. Naturally occurring in most human tissues. Theoretical concern about promoting existing malignancies through angiogenesis. Not FDA-approved for therapeutic use.

## Status sources

- [ClinicalTrials.gov: thymosin beta 4 studies](https://clinicaltrials.gov/search?intr=thymosin%20beta%204)
- [PubMed: RGN-259 ARISE trials](https://pubmed.ncbi.nlm.nih.gov/?term=RGN-259+dry+eye)
- [WADA 2026 Prohibited List](https://www.wada-ama.org/en/prohibited-list)

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Educational reference only — not medical advice. No dosing information is published. Tiers rate the strength of published evidence, not effectiveness or safety.