Thymosin beta-4
Tβ4, TB4, RGN-259
The full 43 amino acid parent protein that TB-500 is a fragment of, and the only version of the two with a completed phase 3 human trial behind it.
Human trials
Not approved. The ophthalmic formulation RGN-259 has completed phase 3 trials for neurotrophic keratopathy and dry eye. The injectable form sold as a research chemical has no approval anywhere.
What it is
Thymosin beta-4 is a naturally occurring 43 amino acid protein found in most human cells and in high concentration in platelets and wound fluid. It binds actin, and through that it regulates cell migration, and through that it turns up in nearly every account of how tissue repairs itself.
The distinction that matters on this site: TB-500 is not this. TB-500 is a synthetic seven amino acid fragment of it, sold on the assumption that the fragment carries the activity. That assumption is reasonable and it is not the same as demonstrated.
Why this entry is rated higher than TB-500
Because the full protein has a completed randomised human trial and the fragment does not.
RGN-259 is thymosin beta-4 as a preservative-free eye drop. In a randomised, placebo-controlled, double-masked phase 3 trial in neurotrophic keratopathy, complete corneal healing at four weeks occurred in 6 of 10 treated patients against 1 of 8 on placebo, and the single healed placebo patient relapsed by day 43 while the treated group did not. Discomfort, foreign body sensation and dryness all improved significantly. No significant adverse effects were reported.
That is a small trial. Eighteen people is not a definitive result, and a corneal surface is not a torn rotator cuff. But it is a real randomised trial of this molecule in humans, published, with a placebo arm, and it puts thymosin beta-4 in a different evidence tier from the fragment people actually inject.
What the evidence does not cover
Nothing here supports injecting it for tendon, ligament or muscle repair. The human data is ophthalmic and topical. The musculoskeletal case rests on rodent work and mechanism, exactly as it does for TB-500, and reviews of that literature keep returning the same finding: no completed randomised human trials in any musculoskeletal tissue.
Practical notes
- The trial-backed product and the vial you can buy are different things. An eye drop with phase 3 data does not transfer its evidence to a lyophilised vial for subcutaneous use. Tier badges on this site describe the use people take a compound for, and for injectable use this one is still riding on the eye data plus mechanism.
- Angiogenesis is the mechanism and also the concern. A molecule whose job is to recruit blood vessels and move cells into a repair site has an obvious theoretical problem in the presence of a tumour. Nobody has run the study that would characterise it.
- If you are choosing between this and TB-500, the honest answer is that neither has injectable human evidence. The parent protein at least has a human trial somewhere in its file.
Side effects and warning signs
Commonly reported
- Injection-site irritation
- Occasional lethargy in the first days of use, self-reported
- Ocular stinging with the eye drop formulation, which is the only route with systematic safety data
Stop and get medical help
- Any active or suspected malignancy. The peptide promotes angiogenesis and cell migration, which are the processes a tumour needs
- Unexplained new lumps or rapidly changing moles during use
Sources
From the community
Discussion for this compound concentrates in r/Peptides and r/PeptideAdvice.
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