What Is TB-500? Structure, Sequence & Evidence

Short definition

TB-500, in the sense FDA now uses for the free base, is a synthetic heptapeptide of 7 amino acids. The conceptual sequence is Ac-LKKTETQ: the 17–23 fragment of thymosin β4 with an acetyl group on the N-terminal leucine.^1,2

It should not be called simply “synthetic thymosin beta-4” without that distinction. A synthetic 43-amino-acid peptide can copy thymosin β4. TB-500, on this record, is a seven-residue fragment. If the word “synthetic” is used to hide the length difference, the reader is given a false identity.

This page answers “what is it” in scientific and regulatory nomenclature. It does not independently verify the contents of a Peptra commercial vial. It does not summarize wounds, interpret tendons, or turn a UNII into an authorization. Those questions have their own pages in the TB-500 research hub.

Seven amino acids

7 residues are not 43. Human thymosin β4 is a 43-amino-acid peptide with a separate identity record. TB-500 takes only the 17–23 window of that chain.^3,1

That window includes the actin-binding region that the Tβ4 literature calls LKKTET or LKKTETQ. Sharing a region does not turn the fragment into the full peptide, and it does not turn the acetylated fragment into the non-acetylated fragment.¹

N-terminal acetylation

The chemical difference most often omitted on commercial pages is the acetyl group. Non-acetylated LKKTETQ and Ac-LKKTETQ are not the same compound. FDA notes that acetylation can change charge, hydrophobicity, size, stability, and folding or binding behavior.¹

A result obtained with non-acetylated LKKTETQ is therefore not copied onto TB-500 as if a trade name absorbed the chemistry. Acetylation is part of the identity, not an ornamental detail.

Relationship to thymosin β4

TB-500 is related to thymosin β4 because its sequence is a fragment of that protein. Related describes a sequence origin. It does not describe biological equivalence, clinical equivalence, or regulatory equivalence.^1,4

FDA puts it in a sentence this page uses as an anchor: websites often use TB-500 and thymosin β4 interchangeably; they are not the same substance.¹

FDA identity record

FDA’s substance registry assigns TB-500 the UNII QHK6Z47GTG. Synonyms include TB-500, TB500, the N-terminal acetylated 17–23 fragment of thymosin beta 4, and N-Acetyl-Leu-Lys-Lys-Thr-Glu-Thr-Gln.²

A UNII is identity information. It does not imply drug approval, final 503A listing, or authorization in Mexico. Full-length thymosin β4 has a different UNII: 549LM7U24W.^2,3

Analytical identification

Esposito 2012 synthesized and characterized the N-terminal acetylated 17–23 fragment identified in a product called TB-500. The identity finding is Ac-LKKTETQ. The work belongs to analytical and anti-doping research.⁴

Ho 2012 describes a detection method for TB-500 in equine urine and plasma. It confirms that the analytical object is a synthetic version of an active region of thymosin β4. It is not a human efficacy trial.⁵

Why the name confusion exists

TB-500 is not a USAN. FDA encountered salts, derivatives, and even different active moieties sold under the same common name. In the nomination file, the name, the certificate, and the CAS numbers did not line up consistently between free base and acetate.¹

That inconsistency is not a catalog footnote. If molecular identity is unclear, evidence cannot be transferred. A paper, a COA, or an advertisement that says only “TB-500” is not enough to know what was studied or sold.

Some catalogs use the same name for 43-amino-acid material consistent with thymosin β4. That illustrates the problem: the trade name does not fix the length. Sequence and mass do. A certificate of analysis is useful precisely because the TB-500 label has covered more than one object.

FDA also separates the free base from the acetate. They are different bulk substances, with different masses, even if they share the same active moiety. A lot, a CAS number, or a certificate that does not say which form was measured leaves identity unfinished.¹

Current direct-human-evidence status

In the 2026 evaluation, FDA did not identify clinical studies or human exposure data using TB-500. That is the dated reading of that review, not a metaphysical sentence.¹

Human trials of full-length thymosin β4 exist and are discussed on other pages in this cluster. They do not enter the inventory of direct TB-500 evidence.¹

Regulatory status, in one sentence

TB-500 is not an FDA-approved drug. In July 2026 it was discussed as a nominated 503A bulk substance, with a staff evaluation against inclusion. WADA lists it in 2026 under S2.3 together with thymosin-β4. None of those facts is a use instruction.^7,1,6

A reader who needs compounding status, the advisory vote, or the human safety gap should go to the regulatory page. This page only fixes the scientific and regulatory identity: 7 residues, Ac-LKKTETQ, distinct from 43-residue Tβ4 and distinct from LKKTETQ without the acetyl group.

Nomenclature and commercial material

Note on nomenclature: the commercial name TB-500 has been used for materials with different molecular descriptions. A lot’s analytical documentation must be reviewed separately and does not automatically imply equivalence with the molecular identity described in the literature or in regulatory documents.

Next reading

• Compare TB-500 and thymosin β4 as different evidence
• See what human studies actually exist
• Back to the TB-500 research hub
• Certificate of analysis archive
• Research-material specifications