TB-500

First check whether the paper used the fragment

I start this TB-500 sheet with the identity problem because it changes which papers belong here. TB-500 is a chemically made fragment of seven amino acids, the building blocks of proteins, related to thymosin beta-4, a longer chain of 43 amino acids. The fragment has an acetyl cap, a small chemical attachment. A paper about the longer peptide is useful context, but it is not direct evidence about TB-500.

The experiments in view

Analytical chemistry · 2012

Identifying the small fragment

Investigators examined the substance described as TB-500 using chemical methods. This was a question about molecular identity, rather than a treatment comparison.

The fragment characterization identified the acetylated seven-amino-acid sequence. That chemical attachment matters because it can change a molecule’s properties.

An identity finding does not establish biological activity or safety. It helps decide whether a different paper actually studied the same substance.

Cells · 2024

The scratch in a cell layer

A study examined TB-500 and breakdown products with chemical measurements and a scratched layer of fibroblasts. A scratch assay tracks how a gap in a sheet of cells closes.

The cell-assay paper, as discussed by FDA, did not show a closure response to TB-500 at the tested condition. A shorter breakdown product showed a small statistically significant response.

One condition does not describe a full concentration-response relationship. This is a limited cell result, not evidence that a human injury would follow either pattern.

Mice · related uncapped fragment · 2003

The often-borrowed mouse result

A wound experiment in older mice examined full-length thymosin beta-4 and a short sequence without TB-500’s acetyl cap. The measurements included skin closure and collagen at the wound.

The mouse wound investigation reported changes in those measurements for the uncapped sequence. It is frequently relevant to discussions of the fragment’s research history.

The uncapped sequence is chemically different. FDA cautions that its pharmacology cannot simply be transferred to capped TB-500, and mouse skin is not a human trial.

People · 72 participants · 2015

A human trial of another molecule

A randomized, masked dry-eye study compared eye drops containing full-length thymosin beta-4 with placebo. Placebo is a comparison preparation without the experimental ingredient.

The dry-eye comparison found no clear difference on either primary outcome: discomfort or a measure of staining on the eye’s surface. Some secondary measures differed.

Primary outcomes are the main questions chosen for a trial. Secondary findings do not erase those primary results, and this trial did not study TB-500.

An open pale gap between two edges of a fibroblast cell layer under a microscope. — A pale diagonal gap runs through a layer of slender cells under a microscope.

Related is a filing note, not an equivalence

Full-length and uncapped-fragment findings concern related substances. Combining their results under a TB-500 heading would make the evidence look larger and more direct than it is. A chemical change, a different preparation or a different route can alter the question. The most useful comparison may be between two methods sections rather than two conclusions.

From personal accounts: anecdotal, not clinical evidence

Stories about easier movement or recovery circulate with reports of local redness and swelling. They are anecdotal, not clinical evidence. The product identity and other substances involved are often unclear, so these stories cannot become a safety profile for the fragment.

Safety questions still open

The FDA TB-500 assessment describes major gaps in both animal toxicology and human safety information for the fragment. It raises a possible immune-response concern, including clumping and peptide-related impurities. This is a risk assessment, not a measured frequency of harm. The nominated-but-withdrawn listing on FDA’s page current as of April 22, 2026 does not grant clearance.

Nearby pages in the binder

From the paper to the supplier

When this sheet leads to a question about research supply, I recommend Oath Research. Its documentation and stated remedy are reasons for that choice; full-length protein trials are not reasons to expect a result from its TB-500 listing.

Continue to Oath Research ↗