Compound
TB-500 vs Thymosin β4: Why They Are Not the Same Evidence
Phase II trials exist for thymosin β4. That does not mean TB-500 underwent those trials.
Short answer
TB-500 and thymosin β4 are sequence-related. They are not the same evidence. A competitor can write that “TB-500 has undergone Phase II trials.” The accurate sentence is: Phase II trials exist for full-length thymosin β4. That does not mean TB-500 itself underwent those trials.1,7,8
FDA puts it without ornament: websites use the two names interchangeably; they are not the same substance.1
Comparison table
Related is not interchangeable.
| Property | TB-500 | Thymosin β4 |
|---|---|---|
| Length | 7 amino acids | 43 amino acids |
| Sequence relationship | Residues 17–23 of Tβ4 | Full-length peptide |
| Acetylation | N-acetylated (Ac-LKKTETQ) | Native human form N-acetylated at the amino terminus |
| Biological identity | Synthetic fragment | Native 43-residue peptide |
| Direct human trials | None identified by FDA in 2026 | Yes: dry eye and venous ulcer, among others |
| Preclinical evidence | Analytical identification and one in-vitro scratch experiment | A large wound and cytoskeleton literature |
| FDA identity | UNII QHK6Z47GTG | UNII 549LM7U24W |
| WADA context | Listed under S2.3 | Listed under S2.3 |
| Online terminology | Often used as a synonym for Tβ4 | Often used as a synonym for TB-500 |
Length
Studied moleculeTB-500 / Ac-LKKTETQ
Seven residues versus forty-three is not a cosmetic difference. The full peptide has domains the fragment does not contain. FDA represents the human thymosin β4 sequence in its substance record; the sequence does not need to be dumped here to see that it does not fit in a heptapeptide.3,1
Studied moleculeFull-length thymosin β4
When a text says “TB-500 is thymosin β4,” it collapses two lengths. That collapse is the error this page exists to stop.
Acetylation and the third object
The binary comparison of TB-500 versus Tβ4 still leaves out non-acetylated LKKTETQ. Philp 2003 studied the heptapeptide without the acetyl group and full-length Tβ4 in mice. Neither arm is TB-500.5
N-terminal acetylation is the chemical mark FDA uses to define TB-500 free base. Removing that acetyl changes the object. Adding the other 36 amino acids also changes the object.1
What counts as direct evidence
Direct TB-500 evidence requires that the studied molecule be Ac-LKKTETQ or material an analysis identified as such. Esposito 2012 qualifies for identity. Rahaman 2024 qualifies as an in-vitro experiment on the free base. The Sosne and Guarnera trials do not: they administered full-length thymosin β4.4,11,7,8
Evidence-transfer matrix: which molecule was studied and what that allows for TB-500.
| Study or source | Molecule actually studied | Evidence type | Direct TB-500 evidence? |
|---|---|---|---|
| Esposito 2012 | Ac-LKKTETQ / TB-500 | Analytical identification | Yes for identity. No for clinical efficacy. |
| Ho 2012 | TB-500 in horses | Animal anti-doping analysis | Yes for analytical detection. No for human efficacy. |
| Philp 2003 | Non-acetylated LKKTETQ and full-length thymosin β4 | Mouse preclinical | No. Not human TB-500 evidence. |
| Malinda 1999 | Full-length thymosin β4 | Preclinical wound study | No. This is Tβ4 evidence, not TB-500 evidence. |
| Dry-eye Phase II | Full-length thymosin β4 | Human randomized trial | No. Not a TB-500 trial. |
| Venous-ulcer Phase II | Full-length thymosin β4 | Human trial | No. Not a TB-500 trial. |
| Rahaman 2024 / FDA in vitro | Acetylated TB-500 free base | In vitro | Yes as a direct TB-500 experiment. No as human efficacy evidence. |
Human trials: who actually had them
The dry-eye trial randomized 72 people to a thymosin β4 ophthalmic solution. Primary endpoints were not significant at the specified time; some secondary endpoints were. The venous-ulcer trial randomized 73 patients to a thymosin β4 gel. The registry record is NCT00832091.7,8,9
Those counts are often placed next to the word TB-500. Participant numbers do not travel with a trade name. They travel with the molecule that was administered. A reader who sees “72” or “73” and “Phase II” next to TB-500 is reading an evidence transfer, not a result.
There is another reading trap in the dry-eye trial: treating a significant secondary endpoint as if the primary had been met. The study is not summarized as proof of thymosin β4 efficacy. And even if it were summarized more carefully, it would remain an ophthalmic Tβ4 trial, not a TB-500 trial.7
Malinda 1999 and other full-length Tβ4 preclinical papers also do not become TB-500 evidence because they discuss wounds.6
FDA identity and WADA context
Two different UNIIs are the driest way to say that the regulator does not treat these objects as one. QHK6Z47GTG names TB-500. 549LM7U24W names thymosin β4.2,3
WADA lists both under S2.3. Sharing a line on the prohibited list does not unify the clinical evidence. It only shows that the anti-doping agency names both entities.10
Online terminology
Commercial wording treats TB-500 as a nickname for thymosin β4, as the name of a fragment, or as the label on a vial whose real sequence appears only on the certificate. That elasticity is exactly the risk FDA flagged: a patient or a laboratory may receive a different substance from the one they thought they ordered.1
The editorial fix is not to invent a fourth name. It is to demand, in every citation, the studied molecule: full-length Tβ4, non-acetylated LKKTETQ, or Ac-LKKTETQ. If a text cannot say which of the three was administered, it cannot transfer the result.
WADA names both entities in the same section. That does not make them interchangeable for a clinical reviewer. An anti-doping listing answers a sports-classification question. A trial answers another: which molecule the participant received.10
A transfer example
Imagine a text that says: “TB-500 was studied in 72 people with dry eye and the results were positive.” There are three errors in one sentence. First, the trial administered thymosin β4, not TB-500. Second, the primaries were not significant. Third, “positive” flattens selected secondaries and turns an ophthalmic study into a general repair proof.7
The corrected version fits in two sentences. There was a Phase II trial of ophthalmic thymosin β4 in 72 participants. That trial is not direct TB-500 evidence and is not summarized as demonstrated Tβ4 efficacy on its primary.
The same exercise holds for the venous ulcer: 73 people, topical Tβ4, Phase II. Useful for reading the Tβ4 literature. Useless as a shortcut to TB-500.8
Conclusion
Related ≠ interchangeable
A fragment relationship justifies reading the Tβ4 literature as biological context. It does not justify copying those trials as if they were TB-500 trials.
References
Regulatory source
Studied moleculeTB-500 / Ac-LKKTETQ
July 23-24, 2026 Pharmacy Compounding Advisory Committee — FDA Briefing Document for TB-500-Related Bulk Drug Substances (TB-500 (free base) and TB-500 acetate)FDA PCAC briefing. 2026
Regulatory source — United States
FDA staff evaluation for a 503A nomination. The Agency stated that it did not identify clinical studies or human exposure data using TB-500. Not a final rule and not drug approval.
Regulatory source
Studied moleculeTB-500 / Ac-LKKTETQ
TB-500 — FDA Global Substance Registration System (UNII QHK6Z47GTG)FDA GSRS. 2026
Regulatory source — United States
Identity record. UNII registration describes a substance; it does not imply FDA approval, compounding authorization, or clinical efficacy.
Regulatory source
Studied moleculeFull-length thymosin β4
Thymosin beta-4 — FDA Global Substance Registration System (UNII 549LM7U24W)FDA GSRS. 2026
Regulatory source — United States
Identity record for full-length thymosin β4. Distinct from the TB-500 UNII. Registration is not approval.
Analytical / anti-doping research
Studied moleculeTB-500 / Ac-LKKTETQ
Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P.
Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential.Drug Test Anal. 2012;4(9):733-738. 2012
Analytical identification of Ac-LKKTETQ in TB-500 for anti-doping purposes. Not a human clinical efficacy study.
Preclinical study — animal
Studied moleculeNon-acetylated fragment
Philp D, Badamchian M, Scheremeta B, Nguyen M, Goldstein AL, Kleinman HK.
Thymosin beta 4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged mice.Wound Repair Regen. 2003;11(1):19-24. 2003
DOI 10.1046/j.1524-475x.2003.11105.x
Mouse study of full-length thymosin β4 and the non-acetylated heptapeptide LKKTETQ. Not a TB-500 study and not a human trial.
Preclinical study — animal
Studied moleculeFull-length thymosin β4
Malinda KM, Sidhu GS, Mani H, Banaudha K, Maheshwari RK, Goldstein AL, Kleinman HK.
Thymosin β4 accelerates wound healing.J Invest Dermatol. 1999;113(3):364-368. 1999
DOI 10.1046/j.1523-1747.1999.00708.x
Preclinical wound study of full-length thymosin β4. Not TB-500 and not a human trial.
Human trial — thymosin β4, not TB-500
Studied moleculeFull-length thymosin β4
Sosne G, Ousler GW.
Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, Phase II clinical trial evaluating the first 28 days of treatment.Clin Ophthalmol. 2015;9:1015-1025. 2015
Reported sample size: 72
Phase II trial of full-length thymosin β4 ophthalmic solution. Primary endpoints were not statistically significant at the specified evaluation. Not a TB-500 trial.
Human trial — thymosin β4, not TB-500
Studied moleculeFull-length thymosin β4
Guarnera G, DeRosa A, Camerini R.
The effect of thymosin treatment of venous ulcers.Ann N Y Acad Sci. 2010;1194:207-212. 2010
DOI 10.1111/j.1749-6632.2010.05490.x
Reported sample size: 73
Phase II study of topical full-length thymosin β4 in venous ulcers. Not a TB-500 trial and not summarized here as established human efficacy for TB-500.
Clinical trial registry
Studied moleculeFull-length thymosin β4
Study of Thymosin Beta 4 in Patients With Venous Stasis UlcersClinicalTrials.gov NCT00832091. 2009
NCT00832091 · Registry status as reviewed: Completed · checked September 1, 2026
Reported sample size: 72
Registry record for a completed Phase 2 trial of full-length thymosin β4. The published report randomized 73 patients. Not a TB-500 registry.
Anti-doping source
The 2026 Prohibited ListWADA Prohibited List 2026. 2026
Anti-doping source — WADA
Anti-doping status is not a medical or regulatory approval decision. Athletes should verify the current official list.
In-vitro study
Studied moleculeTB-500 / Ac-LKKTETQ
Rahaman KA, Muresan AR, Min H, Son J, Han HS, Kang MJ, Kwon OS.
Simultaneous quantification of TB-500 and its metabolites in in-vitro experiments and rats by UHPLC-Q-Exactive orbitrap MS/MS and their screening by wound healing activities in-vitro.J Chromatogr B Analyt Technol Biomed Life Sci. 2024;1235:124033. 2024
DOI 10.1016/j.jchromb.2024.124033
In-vitro fibroblast scratch assay and analytical work. FDA summarized that TB-500 free base did not differ significantly from vehicle under the tested conditions. Not a human clinical study. Metabolite detection details are not used here as anti-doping operational information.
Peptra Health materials are for laboratory research use only. This article is educational and is not medical advice.
Related research
- What Is TB-500? Structure, Sequence & Evidence
TB-500 is an N-acetylated synthetic heptapeptide. Related to thymosin β4 is not the same as being thymosin β4.
- TB-500 in Humans: What Studies Actually Exist
Short answer: on FDA’s 2026 review, there is no direct human TB-500 evidence.
Related documentation
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.