⚔️ Head-to-head
TB-500 vs Thymosin Beta-4
Pep lines up the two side by side — verdict, mechanism, and the dimensions that actually differ — so you can see where each one wins.
By MrPepTalks Editorial · Updated 2026-07-26
TB-500
Thymosin Beta-4
riskyThymosin Beta-4
Timbetasin · TB4
unprovenTB-500
Dimension
Thymosin Beta-4
A short synthetic peptide sold under a product name. When a doping-control laboratory at Ghent University took a commercial TB-500 formulation apart in 2012 and characterised what was inside, what they identified, and then reproduced by synthesis, was a seven-residue fragment of thymosin beta-4 with an acetyl group on the front: Ac-LKKTETQ. TB-500 is a trade label for that fragment, not a scientific name for the protein.
What the name refers to
A protein the human body makes for itself, catalogued as UniProt P62328 and produced by the gene TMSB4X. It is one specific molecule with a defined sequence, a nonproprietary drug name (timbetasin), and decades of published biology behind it. Our [thymosin beta-4 data sheet](/peptides/thymosin-beta-4) covers it in full.
Seven amino acids. In the numbering of the mature protein it corresponds to residues 17 to 23, which is a short stretch from the middle of the parent molecule and nothing else.
Molecular size
Forty-three amino acids in the mature chain, running from residue 2 to residue 44 of the gene product, with the first serine carrying an acetyl group. The first four residues of that chain, AcSDKP, are themselves a separately studied bioregulatory peptide, which is a reminder that different pieces of this protein do different things.
Seven residues out of forty-three, taken from the middle. Whether a fragment that size folds, binds, or behaves like the intact protein is an empirical question, and for this fragment nobody has published the answer.
How much of the parent molecule you get
All of it. This is the molecule the published thymosin beta-4 literature is about, and the one the human trials used.
The agency does not treat the two as interchangeable, and neither should a buyer. Its compounding safety list carries a separate entry reading, in its own words, thymosin beta-4, fragment (LKKTETQ), also known as TB-500. The entry states that no human exposure data have been identified for drug products containing the fragment. The FDA has not approved it for any use. On 23 July 2026 its Pharmacy Compounding Advisory Committee took up TB-500-related bulk substances for discussion, which is a meeting agenda and not a finding.
How the FDA describes it
The full protein is not on that list under its own name, and the FDA has not approved any thymosin beta-4 medicine either. The distinction that matters is that the agency defines TB-500 by the seven-residue fragment, so the regulator itself draws a line between the sold product and the studied protein.
We could find no registered human trial of the TB-500 fragment that we were able to verify as a genuine study. Searching the public registries in July 2026 turned up nothing we would put our name to. For a compound this widely sold, the honest count of trustworthy human trial records is zero.
Registered human trials
A real clinical programme exists. RegeneRx Biopharmaceuticals ran three placebo-controlled Phase 2 studies of a thymosin beta-4 preparation in wounds: pressure ulcers (NCT00382174, 72 participants, completed), venous stasis ulcers (NCT00832091, 72 participants, completed), and epidermolysis bullosa (NCT00311766, 30 participants, terminated early, funded in part by the FDA Office of Orphan Products Development). ReGenTree ran a 601-participant Phase 3 eye study, ARISE-2 (NCT02974907), which completed in 2018 and posted its results.
Nothing, because there is nothing to report. Any page citing trial outcomes for TB-500 is citing outcomes belonging to a different molecule.
What the human results actually showed
Mostly disappointment, which is worth knowing before borrowing the data. In ARISE-2 both co-primary endpoints were measured as change from baseline at day 29, and on both, higher is worse. Ocular discomfort moved 0.07 on the active drop against minus 0.04 on placebo; corneal staining moved 0.07 against minus 0.01. The confidence intervals overlap heavily and neither endpoint favoured the active arm. Borrowing this literature does not borrow a win.
A PubMed search for the exact string TB-500 returned 16 records when we ran it on 26 July 2026, and most of those are analytical-chemistry papers about detecting the compound in urine or plasma for doping control rather than studies of what it does in a body.
Volume of published research
The same search for thymosin beta 4 returned 1,031 records. That roughly sixty-fold gap is the whole reason the conflation happens: one name has a literature to cite and the other does not.
The mechanism usually printed on sales pages is the parent protein's. Whether the seven-residue fragment reproduces it has not been established in any publication we could find. The LKKTETQ stretch is often called the actin-binding domain, but a binding motif lifted out of its protein is a hypothesis about function, not a demonstration of it.
Described mechanism
UniProt records the function directly: it binds and sequesters actin monomers, the G-actin pool, and so inhibits actin polymerisation. That places it in the middle of how a cell organises its skeleton and how it moves, which is why laboratories keep testing it in wound, cornea and cardiac models. A well-characterised molecular job is still a long way from a measured outcome in a person.
Effectively none for the fragment as sold. The FDA states it has identified no human exposure data for products containing it, and flags possible immunogenicity risk for certain routes because of aggregation potential and peptide-related impurities. There is no published trial safety database to fall back on.
Safety information available
Some, and all of it from surfaces that are not how people use the gray-market product. The completed studies were a gel on a wound and a drop in the eye. In ARISE-2, serious adverse events occurred in 3 of 299 on the active drop and 2 of 302 on placebo over 28 days. That tells you about eye drops. It tells you nothing about an injectable product used over months.
Prohibited, and named. The WADA 2026 Prohibited List gives TB-500 as the worked example of a thymosin beta-4 derivative under section S2.3, growth factors and growth factor modulators. Everything in S2 is prohibited at all times, in and out of competition, and is non-Specified, the category carrying the heavier default sanction.
Anti-doping status
Prohibited under the same line, which names thymosin beta-4 and its derivatives together. Listing the parent and its derivatives in one breath is deliberate: an athlete cannot argue that the label said TB-500 rather than thymosin beta-4. [Are peptides banned in sports](/learn/are-peptides-banned-in-sports) has the wider list.
Unverified. The 2012 characterisation found the seven-residue fragment in the formulation the laboratory tested; it does not certify what any other seller ships. Because the label is a product name rather than a chemical name, two vials marked TB-500 need not contain the same thing. A certificate of analysis naming the actual sequence is the only way to know, and [how to read a peptide COA](/learn/how-to-read-a-peptide-coa) explains what to look for.
What is actually in the vial
Rarely what is on offer. Material sold to consumers is almost always labelled TB-500, so a buyer wanting the full protein is usually not being sold it. [Gray-market peptides](/learn/gray-market-peptides) covers the wider supply problem.
Not by accident, and not always dishonestly. A seller needs citations, the fragment has almost none, and the parent protein has over a thousand papers. Substituting one for the other fills the page. The result is a reader looking at evidence about a molecule they are not buying.
How the confusion happens
The protein is the innocent party here. Its literature is real, its trials are real, and its results are mixed and public. It simply gets recruited to vouch for something a sixth its size. Two 2026 narrative reviews, one in the American Journal of Sports Medicine and one in Sports Medicine, list thymosin beta-4 and TB-500 as separate entries rather than folding them together, which is the correct handling.
TB-500 is a seven-residue fragment with no verifiable human trial record and no human exposure data identified by the FDA. Judge it on its own evidence, which is close to empty, and see our [TB-500 data sheet](/peptides/tb-500) for the rest. If you came here from the [BPC-157 versus TB-500 comparison](/compare/bpc-157-vs-tb-500), this is the identity problem that page flags.
Bottom line
Thymosin beta-4 is a 43-amino-acid human protein that has genuinely been through placebo-controlled trials and largely did not separate from placebo in the ones that reported. Both facts matter. The evidence is real, the results are unflattering, and neither of those things transfers to a different molecule sold under a different name.
TB-500 data sheetThe terse reference: facts, forms, and Pep's verdict.Thymosin Beta-4 data sheetThe terse reference: facts, forms, and Pep's verdict.
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