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TB-500 (Thymosin Beta-4 Fragment): What the Evidence Actually Shows

Grade C, preclinical onlyNot legal to compoundWADA prohibited

Status first

TB-500 is not currently legal to compound in the United States. An FDA advisory committee recommended adding it to the 503A bulks list on 23 July 2026, but that vote is advisory and formal rulemaking has to complete before anything changes. Sites announcing it is "legal now" are wrong.

The short version

A synthetic fragment of thymosin beta-4, a naturally occurring actin-binding protein.
Marketed for soft tissue repair, tendon healing and reduced scarring.
Human evidence is essentially absent. The literature is animal work and mechanism.
Almost always sold alongside BPC-157. Neither is currently available legally.
Prohibited by WADA. It will show on a drug test.

What it is

Thymosin beta-4 is a real protein found throughout the body that plays a role in cell migration and wound repair. TB-500 is not that protein. It is a shorter synthetic fragment of it, chosen because it is cheaper to make and easier to handle. That distinction gets blurred constantly in marketing, where the research on the full protein is presented as though it applies to the fragment.

What the research shows

The animal literature on thymosin beta-4 is genuine and reasonably extensive, covering corneal healing, cardiac repair after injury and dermal wound closure. Some of that work reached early human trials for specific ophthalmic and cardiac indications.

What does not exist is human evidence for the way TB-500 is actually marketed: injected by athletes for tendon and muscle recovery. There are no controlled trials in that population, and the fragment has not been shown to reproduce the full protein's effects in humans.

The fair framing

This is not a compound with disproven claims. It is a compound with untested ones. The mechanism is plausible, the animal data is real, and the human data has simply never been generated. Those are different things and most content on TB-500 collapses them.

What this will not do

It will not come with human efficacy data, because none exists.
It will not be legally obtainable until FDA completes rulemaking.
It will not fix a structural tear. Get it imaged.
It will not clear a drug test.

Safety

The honest answer is that the safety profile in humans is not well characterised, because the studies that would characterise it have not been done. Theoretical concerns centre on angiogenesis, since a compound that promotes new blood vessel growth is a compound worth thinking carefully about in anyone with a cancer history. Discuss that with an oncologist, not a forum.

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Regulatory status current as of the page date. This area is changing quickly and this page is reviewed monthly. [set review reminder]