TB-500: the trials belong to a different molecule

What this comes down to

• Thymosin beta-4 returns 1,131 PubMed records and seven randomized trials in humans. The TB-500 fragment returns 26 records and zero.
• The FDA lists the fragment by its sequence — thymosin beta-4, fragment (LKKTETQ), also known as TB-500 — and says it has not identified any human exposure data for it.
• The trials that do exist tested the full protein as eye drops for severe dry eye, as an intravenous infusion in healthy volunteers, and on venous leg ulcers. None of them is the use TB-500 is marketed for.
• No seller on our price roster publishes a TB-500 line at all, while the identical kind of search finds sermorelin on dozens of them.

They are not the same thing

Thymosin beta-4 is a naturally occurring 43-amino-acid protein that sequesters actin and has been studied in wound repair for decades. TB-500 is a synthetic seven-residue fragment, LKKTETQ, taken from the actin-binding region. Marketing treats the fragment as a cheaper, more stable version of the protein. The literature treats them as different subjects: search the fragment's own names and you get 26 records, against 1,131 for the protein^[1].

("TB-500"[tiab] OR "TB 500"[tiab]) AND "randomized controlled trial"[pt] AND "humans"[mh]

What the seven trials actually tested

Reading them one by one is the fastest way to see the gap. A phase 2 trial gave thymosin beta-4 as 0.1% eye drops to nine patients with severe dry eye, some of it associated with graft-versus-host disease, over 56 days^[2]. A phase 1 study infused it intravenously into healthy volunteers to establish tolerability^[3]. A first-in-human phase 1 of recombinant human thymosin beta-4 ran in healthy Chinese volunteers in 2021^[4]. The rest are venous leg ulcers and a cell-therapy pilot in myocardial infarction.

What the FDA wrote about the fragment specifically

The agency's compounding page lists it under its sequence, which is itself informative — it is identifying the fragment, not the protein^[5].

“Compounded drugs containing thymosin Beta-4, Fragment (LKKTETQ) may pose risk for immunogenicity for certain routes of administration due to the potential for aggregation as well as peptide-related impurities. FDA has not identified any human exposure data drug products containing Thymosin Beta-4, Fragment. FDA lacks important information regarding any safety issues raised by this drug, including whether it would cause harm if administered to humans.”

^[5]

It sits in the table of nominations that were later withdrawn by whoever filed them, which removes the substance from the queue for the bulks list and leaves the agency's text published beside the name. The status table records where each of these peptides landed. And the phrase that recurs — peptide-related impurities, aggregation — is the same one the FDA uses for BPC-157, CJC-1295 and ipamorelin, which is a fact about how these things are made rather than about what they do.

Nobody we have read sells it by name

Across the 190 sellers on our roster, not one publishes a priced TB-500 line — and the pattern we used would also have caught a seller writing "thymosin beta-4" instead. The same kind of pattern, run in the same pass, found sermorelin on 38 sellers and BPC-157 on four, so the zero is a fact about the menu rather than about the search. Where TB-500 does show up is in the gray market the sports medicine reviews describe — sold as a research chemical rather than on a prescription^[6].

If a company does offer it to you, the questions are the same ones we would ask about any compounded peptide: which pharmacy, which grade of material, and what happens if you react to it.

Questions people actually ask