TB-500: Identity, Evidence & Its Relationship to Thymosin β4

Overview

The main difficulty in evaluating TB-500 is that much of the online literature mixes three related but different molecules: full-length thymosin β4, the LKKTETQ fragment, and the N-acetylated fragment Ac-LKKTETQ identified as TB-500.

FDA currently describes TB-500 free base as a seven-amino-acid synthetic fragment corresponding to thymosin β4 residues 17–23, with an acetyl group on the N-terminal leucine. That is a chemical-identity statement. It is not a drug authorization and not a finding of efficacy.^1,4

The same 2026 evaluation records a fact that many websites omit: TB-500 and thymosin β4 are frequently used as if they were the same name. FDA states that they are not the same substance.¹

The three molecules that are usually confused

Related is not interchangeable. A claim about wounds, tendons, or “Phase II” is direct TB-500 evidence only if the molecule administered or analyzed was TB-500.

How TB-500 was identified

In 2012, Esposito and colleagues synthesized and characterized the N-terminal acetylated 17–23 fragment of thymosin β4 that they identified in a product sold as TB-500. The material was Ac-LKKTETQ.⁶

That paper is analytical and anti-doping research. It establishes identity of a material. It does not measure human wound repair and it does not replace a clinical trial.⁶

A second 2012 analytical study, in equine urine and plasma, also treats TB-500 as a synthetic version of an active region of thymosin β4. It is animal detection work, not human efficacy evidence.⁷

Evidence map

Is there human evidence for TB-500?

Direct human TB-500 evidence: none identified by FDA in its review. The Agency wrote that it did not identify clinical studies or human exposure data using TB-500. That reading is dated to the 2026 evaluation. It is not a permanent universal negative.¹

That gap is not filled by trials of another molecule. A full-length thymosin β4 trial does not become a TB-500 trial because both names appear on the same commercial page.^1,13

What evidence exists for full-length thymosin β4

Human research of 43-amino-acid thymosin β4 does exist. A Phase II dry-eye trial randomized 72 participants. The primary endpoints — ocular discomfort and inferior corneal staining — did not show statistically significant differences at the specified primary evaluation. Some secondary endpoints were significant. That is not summarized as “Phase II proved efficacy.”¹³

Another Phase II trial evaluated topical thymosin β4 in venous ulcers and randomized 73 patients. The matching registry record is NCT00832091. This is human research of full-length Tβ4. It is not a TB-500 program.^14,15

Those pages should be read with their own molecule in view. The question “was there a Phase II trial?” has a yes for thymosin β4. The question “did TB-500 undergo those trials?” has a no, on the record FDA reviewed.¹

What we know about wound-healing claims

The use FDA evaluated for the compounding nomination was wound healing. The problem is not that a wound literature exists in this peptide family. The problem is that the literature usually studies full-length Tβ4 or non-acetylated LKKTETQ and is then presented as if it were TB-500.^1,8,9

Philp 2003 applied thymosin β4 and the non-acetylated heptapeptide LKKTETQ in mouse models. FDA notes that acetylation changes charge, hydrophobicity, size, stability, and folding or binding behavior. The pharmacological profile of non-acetylated LKKTETQ therefore cannot be directly extrapolated to TB-500.^8,1,11

In the in-vitro experiment FDA described, TB-500 free base did not produce a statistically significant difference versus vehicle in fibroblast scratch-wound closure. A metabolite, N-acetylated LKKTE, produced a small significant effect under the same conditions. That does not authorize the sentence “TB-500 does not work.” It shows that fragment, metabolite, and full-length Tβ4 evidence cannot be casually combined.^12,1

FDA 2026

On July 23, 2026, the Pharmacy Compounding Advisory Committee discussed TB-500 free base and TB-500 acetate for the 503A Bulks List. The use evaluated was wound healing. FDA staff concluded that the available evidence weighed against including both forms.^2,1

Staff reasons included incomplete chemical characterization, inconsistent naming, absence of human clinical evidence, limited safety information, immunogenicity and aggregation concerns, and lack of direct effectiveness evidence.¹

Trade and professional reporting describes an advisory committee vote in favor of inclusion, commonly given as 8 yes, 6 no, and 1 abstention. That tally comes from specialized press, not from official minutes cited here. The vote is advisory. It does not approve TB-500 as a drug, does not establish efficacy, does not place it automatically on the final 503A list, and does not create authorization in Mexico.^16,3

WADA 2026

The 2026 WADA Prohibited List includes thymosin-β4 and TB-500 under section S2.3, growth factors and growth factor modulators. That fact classifies an anti-doping status. It is not a medical decision and not use guidance.¹⁷

This page does not describe detection windows, washout timing, operational metabolites, or strategies to avoid a test. Classification and source are enough.

What we do not know

• There is, in FDA’s 2026 review, no human clinical trial that administers TB-500 with a clear analytical identity.
• We do not know whether findings from full-length Tβ4 or non-acetylated LKKTETQ would repeat with Ac-LKKTETQ in people.
• There is no final FDA rule, as of this review date, adding TB-500 to the 503A Bulks List.
• The trade name TB-500 has covered salts, derivatives, and, in catalogs, even full-length material. Without sequence and mass, the name does not identify the molecule.

Explore Research

• What is TB-500? Structure, sequence, and evidence
• TB-500 vs thymosin β4: why they are not the same evidence
• TB-500 and LKKTETQ: the actin fragment
• Wounds and tendons: what evidence is direct
• TB-500 in humans: what studies exist
• FDA, compounding, and WADA status

Analytical documentation

A certificate of analysis can document what a lot’s analytical record reports: identity, purity, and method. It does not convert thymosin β4 or LKKTETQ evidence into clinical evidence for that material. The name on the vial does not transfer trials.¹

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.

See the TB-500 certificate archive and the research-material specifications. Also read how to read a peptide COA.