Peps
Two names, two different molecules
Thymosin beta-4 is a natural 43-amino-acid protein found in most cells, where it helps manage the actin skeleton that lets cells move and change shape. "TB-500" is a seller name, not a scientific one. It is usually described as a short synthetic piece of thymosin beta-4 built around the sequence LKKTETQ, one of the regions researchers linked to cell migration.
Because sellers do not always state exactly what their TB-500 contains, the first question for any listing is which molecule it is: the full protein, a defined fragment, or something else. Our TB-500 profile notes where a seller describes the full-length sequence instead.
Source: Biological activities of thymosin beta4 defined by active sites in short peptide sequences. ↗
What the fragment research shows
A 2010 review mapped thymosin beta-4's activities to short regions of the protein. The LKKTETQ region was associated with cell migration and wound-related activity in laboratory work, while other regions were linked to different effects such as anti-inflammatory signaling.
That mapping is useful biology, but it is mechanism research. It does not show that a synthetic fragment repairs tendons, muscles or injuries in people, and no controlled human trial of a fragment sold as TB-500 was found when this guide was checked.
Source: Biological activities of thymosin beta4 defined by active sites in short peptide sequences. ↗
The human trials used the full protein in eye drops
The best-known human studies tested RGN-259, an eye-drop form of full-length thymosin beta-4, for dry eye. In the larger phase 2 trial, neither primary outcome (eye discomfort and corneal staining at day 29) improved significantly compared with the vehicle, although some secondary outcomes favored treatment.
A smaller trial in severe dry eye reported improvements at day 56 and described the drops as well tolerated. Both studies concern eye drops in eye disease. They say nothing about injected fragments or about healing elsewhere in the body.
Safety: the regulator's view
The FDA lists "thymosin beta-4, fragment (LKKTETQ), also known as TB-500" among bulk drug substances for compounding that may present significant safety risks. It notes possible immune reactions and impurity concerns and says it has not identified any human exposure data. Neither TB-500 nor thymosin beta-4 is an approved medicine in the U.S.
So the honest comparison is this: thymosin beta-4 has a few small, mixed human trials in one narrow use, and TB-500 has laboratory mechanism work but no comparable human evidence. Evidence about one cannot simply be borrowed for the other.
Continue with the original research
Study examples are based on selected publication abstracts and the explicitly described source documents. This is not a systematic review or an individualized treatment guide. Editorial scope and methods.