What is TB-500?

What is TB-500, in specification terms

What is TB-500 in the narrowest sense the word specification allows? A short synthetic peptide, seven residues long, acetylated at the N-terminus: leucine, lysine, lysine, threonine, glutamate, threonine, glutamine, written Ac-LKKTETQ. Its molecular formula is C38H68N10O14 and its average molar mass 889.018 g/mol, which a certificate will normally round to 889.0. It is registered under CAS 885340-08-9.

Seven residues makes it a heptapeptide, and that word is worth recognising because it is how the analytical and anti-doping literature refers to it when the trade name is avoided. Physically it is supplied as a white lyophilized powder, normally as a cake rather than a loose solid, readily soluble in bacteriostatic water for peptides. The rules in how to store peptides apply to it unchanged: −20°C for the long term, 2 to 8°C once it is in solution. In this catalogue it ships as a 10mg vial released at 99.58% purity by HPLC.

The acetyl group on the N-terminus is not decoration. Capping the free amine removes a charged end and makes the short chain considerably less attractive to aminopeptidases, which is the usual reason a fragment this length is supplied acetylated rather than free. The N-terminus, the residue count and the Ac- prefix are the vocabulary of what is a peptide, which is the page to read first if any of it is unfamiliar.

TB-500 is a catalogue designation rather than a chemical name, and catalogue designations drift. The registry identifiers below are the only unambiguous way to state which molecule is meant, and they are worth keeping to hand when comparing a listing, a paper and a certificate that all use different words for the same thing, or the same words for different things.

What is TB-500 a fragment of? Residues 17 to 23 of thymosin beta-4

Thymosin beta-4 is a real protein: 43 amino acids, roughly 4,963 daltons, present in most cell types and the main molecule responsible for holding monomeric actin in reserve inside a cell. It is abundant, it was first isolated from thymus tissue in 1981, and it has been studied for decades.

TB-500 corresponds to positions 17 to 23 of that chain. Those seven residues contain the LKKTET motif, which the beta-thymosin literature identifies as the actin-binding region of the protein, and that is the reason this particular stretch was worth synthesising on its own rather than any other seven. The motif was pinned down through the 1990s, after the parent protein had already been established as a major regulator of the cell's unpolymerised actin supply.

The names are used interchangeably almost everywhere, and they should not be. A fragment is not the protein it was taken from: it lacks the rest of the structure, and preclinical findings on full-length thymosin beta-4 do not transfer to a seven-residue fragment as a matter of course. Where a study says one, it means one.

Arithmetic is the quickest guard against the confusion. 889 daltons against about 4,963 is a factor of roughly five and a half, so any mass spectrum separates the two without anyone needing to trust a label. That is also why the identity line on a certificate carries more weight here than the purity line does, and why what is TB-500 is a question better answered with a mass than with a name.

What is TB-500 called on a label, and what each name denotes

Punctuation is the first thing to get past. TB-500, TB500 and TB 500 are the same designation with different punctuation, and all three turn up on labels and in papers. Tβ4, Tb4 and TB-4 are not: those are abbreviations for the 43-residue parent protein, and a page that mixes them with TB-500 in the same paragraph is describing two molecules as though they were one.

The ambiguous case is a label reading Thymosin Beta-4 Acetate. It may mean the full protein supplied as an acetate salt, or it may mean the acetylated fragment, and the words alone do not settle it. The mass on the certificate does: 889.0 for the fragment, around 4,963 for the protein.

This is not only other suppliers' problem. Four of our own blend certificates name that component Thymosin Beta-4 rather than TB-500, three GLOW lots and one KLOW lot, because that is what the testing laboratory wrote on the report, and the GLOW and KLOW pages list it the way the certificate does rather than quietly correcting the document after the fact. The certificate is the record; tidying its wording would make it a worse record.

Two further molecules attract the same confusion for different reasons. Thymosin alpha-1, or thymalfasin, shares a family name and nothing else: 28 residues, acetylated, derived from a different precursor protein called prothymosin alpha, with its own separate literature. BPC-157 shares no sequence at all. It is a 15-residue synthetic peptide, GEPPPGKPADDAGLV, of 1419.53 g/mol, and it collects the same confusion only because the two are so often studied and sold side by side. BPC-157 vs TB-500 sets them out properly, the BPC-157 peptide is described on its own terms elsewhere, and the Repair Reference Panel supplies the pair as separate lot-matched vials rather than as a mixture, because a blend cannot be assayed component by component as cleanly as two vials can.

What is TB-500 studied for in the preclinical literature

Three areas recur in answer to what is TB-500 studied for. Actin sequestration, which is the mechanism the parent protein is known for and the reason this particular region was isolated. Cell migration, usually measured as migration rate in scratch-assay model systems. And angiogenesis markers in vascular-repair endpoints.

The actin work is the oldest and the most quantitative. Sanders, Goldstein and Wang established in PNAS in 1992 that thymosin beta-4 is a major regulator of the pool of unpolymerised actin inside a living cell, pairing with it at roughly one to one; binding strengths in the region of 0.5 to 0.7 micromolar appear in the beta-thymosin literature. Every one of those figures describes the 43-residue protein. None of them was measured on the seven-residue fragment, and quoting them for TB-500 is the error this article keeps returning to.

The chronology is short and explains why a fragment exists at all. Thymosin beta-4 was isolated from thymus tissue and sequenced as a 43-residue peptide in 1981. The 1992 PNAS work established it as a major regulator of the cell's unpolymerised actin supply. Through the 1990s the LKKTET region was identified as the actin-binding motif, which is the point at which synthesising those residues alone became a sensible thing to do rather than an arbitrary one. Work from the 2000s onward extended from sequestration into migration rate and vascular-repair endpoints. That work too was carried out, for the most part, on the parent protein.

Downstream of that sit the terms a reader will meet across the literature: G-actin sequestration, cytoskeletal organisation, endothelial and fibroblast migration, extracellular-matrix endpoints, and wound-closure and tendon or ligament model systems in animals. These are descriptions of what was measured and in what preparation, not of outcomes in people.

All of it is in-vitro and animal model work. None of it is an efficacy claim, and nothing on this site describes what TB-500 does in a person: it is supplied strictly for laboratory research use.

Where thymosin beta-4 studies get cited as TB-500 evidence

The substitution is so routine that it is worth stating as a rule: when a page selling TB-500 cites decades of research, check which molecule the research used. Most of the well-known numbers in this subject, the one-to-one actin pairing, the micromolar binding figures and the wound-model results, were generated with the full 43-residue protein, and often in preparations that have nothing to do with a lyophilised vial.

That observation is no longer confined to chemists. In its 2026 review of the material the FDA recorded that the wound-healing studies submitted in support of it had used the full protein, and that no human study had administered TB-500 itself. Public chemical and anti-doping references say the same thing more bluntly: there are no completed human trials of this fragment.

This matters commercially as well as intellectually. A supplier page that presents parent-protein findings as evidence for a fragment is either not reading its own citations or is counting on the reader not to, and either way it tells you something about the quality of the rest of the page. How to vet a research peptide supplier starts from the same instinct: follow the specific claim back to the specific document.

The compliant version of the point is simple. A study of thymosin beta-4 is evidence about thymosin beta-4. A study of Ac-LKKTETQ is evidence about Ac-LKKTETQ. Neither is evidence about anything happening in a person, because that work has not been done.

How a peptide this short is made

By solid-phase synthesis, which is how effectively all short peptides are built. The C-terminal residue is anchored to a resin bead and the chain is extended one residue at a time: deprotect, couple, wash, repeat. The growing peptide is held in place by the bead throughout. At seven residues that is six coupling cycles, plus the acetylation step at the end.

Short chains are forgiving. Each coupling is slightly less than perfect, and those small failures compound with length, which is why a fifty-residue peptide is a much harder product than a seven-residue one and why purity figures across this category are so consistently high at the short end.

The peptide is then cleaved from the resin, purified by preparative HPLC, usually with trifluoroacetic acid in the mobile phase, and lyophilised. That mobile phase is where the counter-ion in the finished vial comes from, and it is one of the things a figure for peptide purity does not describe.

The characteristic failure of a short synthesis is a deletion: one coupling that did not go, giving a chain missing a residue. On a seven-residue peptide that shifts the mass by between 101 and 129 daltons depending on which residue is absent. A purity percentage can miss a deletion sequence entirely if it co-elutes closely enough; a mass spectrum cannot, because the observed mass simply is not 889.0. That asymmetry is the whole argument for reading the identity line before the purity line.

What is TB-500 in a 10mg vial, once water and counter-ion are counted

Not the label strength, which is where most readers start. The label strength is a nominal fill of lyophilised solid, and that solid is not pure peptide by mass. It also holds residual water left after lyophilisation and the trifluoroacetate counter-ion carried over from purification. This is why a certificate reports purity and content as two separate lines: purity says what proportion of the peptide present was the intended sequence, and content says how much material was measured in the vial.

Ours run over the label rather than under it. Across the three released lots of TB-500 in the certificate library, measured content has been 12.16mg, 11.49mg and 10.85mg against a 10mg nominal fill, with HPLC purity between 99.58% and 99.859% and identity confirmed by LC-MS against a certified reference standard on every one. The current lot also carries an endotoxin result: LAL, pass on both replicates at ≤0.05 EU/mL. That is a test a good many certificates in this category simply do not run.

It is worth knowing what does not need checking at this size. Aggregation, higher-order structure and immunogenicity dominate the quality control of a therapeutic protein, and a seven-residue chain has almost none of that behaviour available to it: no fold to lose, little surface with which to self-associate. What replaces those concerns is narrower and more mundane: a deletion sequence from an incomplete coupling, the counter-ion load, residual water, and whether the material was handled cleanly enough to pass an endotoxin test. A certificate that reports the second set is answering the questions a short peptide actually raises rather than the ones borrowed from protein manufacturing.

Three lots is not a large dataset and the figures are not offered as a specification. They are offered because a released lot with a real number beside it is a different kind of statement from a category-wide claim about typical purity, and the difference is the only thing that separates one 10mg vial from another once both say 99% on the listing.

Reconstitution arithmetic for a 10mg vial

Concentration is mass divided by volume, and nothing about TB-500 makes that arithmetic special. A 10mg vial taken up in 1ml of diluent gives 10mg/ml; in 2ml it gives 5mg/ml; in 5ml it gives 2mg/ml. The table below extends that to the volumes most often prepared. It is concentration arithmetic for making up a stock solution in a laboratory. It is not a dose, and nothing here is guidance for administering anything to anyone.

Bacteriostatic water is the usual diluent because it sits at a mildly acidic, unbuffered pH around 5.7 and carries 0.9% benzyl alcohol as a preservative, which is what allows a multiple-dose container to be entered more than once within its in-use period of 28 days. Sterile water vs bacteriostatic water comes down to that preservative and to nothing else: sterile water carries none at all, which is the reason a vial reconstituted with one is handled differently from a vial reconstituted with the other.

Mechanically: run the diluent slowly down the inside wall of the vial rather than onto the cake, and swirl rather than shake. A seven-residue peptide is not fragile, but foaming a solution wastes material at the meniscus and makes an accurate volume harder to take. Once in solution the material goes to 2 to 8°C rather than back to the freezer, and the rules in how to store peptides are the same for this material as for every other lyophilised peptide here.

Reading a TB-500 certificate of analysis

Because it is short, TB-500 is an easy synthesis, and peptide purity testing across this category returns correspondingly high figures. That makes purity a weak signal on its own, and identity the more informative one: a mass-spectrometry result showing observed mass against a theoretical 889.0, read the way a peptide certificate of analysis should be read, tells you the seven residues are the right seven in the right order and the acetyl group is present.

Then the lot number. A certificate describes one batch, and unless the number on it matches the number on the vial it describes someone else's batch. Ours are published before purchase, matched to the vial, and can be looked up directly by lot.

The table below is what to look at, field by field, and what a value that is evading the question looks like. Most of the certificates circulating in this category fail on the last two rows rather than the first: the chemistry is fine and the traceability is absent.

What is TB-500 in regulatory and anti-doping terms, and how it is detected

Ask what is TB-500 in law rather than in chemistry and the answer is unusually tidy: none of the pharmacology is settled and all of the status is. TB-500 is not an approved drug. A US advisory committee recommendation in July 2026 concerning the 503A Bulks List has been widely reported as though it were an approval; it is not one, and a recommendation to a list of substances that may be used in compounding is a different instrument entirely. Public references record it as a prescription medicine in Australia and New Zealand.

In sport the position is unambiguous. The World Anti-Doping Agency's 2026 Prohibited List covers it in and out of competition; anti-doping summaries place it under S0, unapproved substances, and S2, peptide hormones and growth factors. The Banned Substances Control Group reports a four-year sanction handed to a Canadian athlete on a non-analytical finding involving BPC-157 and TB-500. Non-analytical means the case rested on evidence other than a positive sample.

Which brings the subject back to chemistry, because the detection work is the most interesting analytical literature attached to this molecule and almost nobody writing about it covers it. TB-500 appeared first as a designer drug in racehorses, and equine laboratories built LC-MS/MS methods to find Ac-LKKTETQ and its breakdown products in urine and plasma. A seven-residue acetylated peptide is an awkward analyte: small, cleared quickly, and easily lost among endogenous peptides. Those methods therefore target the metabolite pattern as much as the parent, which is a harder piece of method development than a small-molecule screen.

The loop is worth noticing. The same liquid chromatography and tandem mass spectrometry that identifies Ac-LKKTETQ in a doping control laboratory is what confirms identity on the certificate that ships with a research vial. One asks whether the molecule is present in a sample; the other asks whether the molecule in a vial is the one on the label. Same instrument, same principle, opposite question.