Source: https://peakpeptides.com/peptides/tb-500/ Peptide library · Synthetic peptide # TB-500 A synthetic seven-amino-acid fragment, Ac-LKKTETQ, associated with the actin-binding region of thymosin beta-4. Most repair research used the full 43-amino-acid protein, not TB-500 itself. Last reviewed September 22, 2026 At a glance - **Also called:** Ac-LKKTETQ; thymosin beta-4 17-23 fragment - **What it is:** An acetylated seven-amino-acid fragment - **Evidence:** Fragment analytics; parent-protein animals and one human pilot - **FDA status:** Not FDA-approved for any use - **In sport:** Prohibited at all times by WADA - **At Promise Peptides:** Listed; currently waitlist-only The short version TB-500 is the synthetic, N-terminally acetylated sequence Ac-LKKTETQ. It is much shorter than thymosin beta-4, the natural 43-amino-acid protein from which that motif comes. This distinction controls how the evidence reads: most animal repair experiments and the small human safety study tested full-length thymosin beta-4, not TB-500. TB-500 is not FDA-approved. FDA’s current table lists its compounding nomination as withdrawn and retains a safety note. A licensed provider’s clinical decision does not change those FDA facts. ## What it is TB-500 is a synthetic heptapeptide, meaning seven amino acids, with an acetyl group attached at the beginning. Its sequence corresponds to residues 17 through 23 of thymosin beta-4 and includes the parent protein’s LKKTET actin-binding motif. Full-length thymosin beta-4 occurs widely in human cells and contains 43 amino acids. TB-500 itself is a synthetic fragment, not the natural full protein. The sequence is Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH, commonly shortened to Ac-LKKTETQ. Its molecular formula is C38H68N10O14 and reported molecular weight is 889.02 daltons. Anti-doping analytical literature explicitly defines TB-500 as the short fragment.[1] ## Where the research stands Direct TB-500 evidence is largely chemical identification and anti-doping detection. The widely cited tissue-repair studies used full-length thymosin beta-4. They can explain why the short fragment attracted interest, but they do not show that TB-500 reproduces the parent protein’s effects. How far the evidence has climbed 1. Cell studies · Limited · Mostly full-protein or structural work 2. Animal studies · Limited · Repair studies largely use full protein 3. Small human pilots · None · Full protein studied, not TB-500 fragment 4. Controlled human trials · None · No controlled fragment trial 5. FDA approval · No · Not approved for any use Here is what selected studies looked at. Every card says whether it tested TB-500 or full-length thymosin beta-4. - **Partial-protein hybrid: actin binding** (Structural · 2004): X-ray crystallography examined a hybrid containing the C-terminal half of thymosin beta-4 fused to gelsolin G1 and bound to actin. The molecule studied was not full-length thymosin beta-4 or TB-500.[2] - **Full protein: skin wounds** (Rats · 1999): Rats with full-thickness skin wounds received full-length thymosin beta-4. Researchers measured re-epithelialization, contraction, collagen and blood-vessel growth; the fragment was not tested.[3] - **Full protein: heart model** (Mice · 2004): In a mouse coronary-ligation model, researchers measured ILK/Akt signaling, myocyte survival and cardiac function after full-length thymosin beta-4. Cell migration was measured separately in embryonic-heart tissue and cultured cardiomyocytes. The study cannot establish a human or TB-500 outcome.[4] - **Full protein: phase 1 safety** (Humans · 2010): A placebo-controlled phase 1 study gave full-length synthetic thymosin beta-4 to 40 healthy volunteers and measured short-term tolerability and pharmacokinetics. It did not test the TB-500 fragment.[5] - **TB-500: anti-doping detection** (Horses · 2012): An equine analytical study defined TB-500 as the acetylated LKKTETQ fragment and developed a mass-spectrometry method to detect it and its metabolites. It did not test clinical benefit.[1] - **Full protein: a null functional result** (Mice · 2010): In dystrophin-deficient mice, the study measured regenerating muscle fibers, muscle strength, heart function and fibrosis after full-length thymosin beta-4. It did not test the TB-500 fragment or people.[6] ## What the research can’t tell you - **Fragment and parent are not interchangeable**: TB-500 contains only seven residues from a 43-amino-acid protein. A full-protein result cannot establish that the fragment behaves the same way.[1] - **No controlled human fragment trial**: The human phase 1 study used full-length thymosin beta-4. It cannot establish TB-500 safety or effectiveness.[5] - **More repair markers may not mean function**: The mouse muscular-dystrophy study found more regenerating fibers without better strength or heart function.[6] - **A theoretical tumor question**: Full-length thymosin beta-4 influences cell migration and angiogenesis in models. Concern about tumor biology is mechanism-based, not a finding in people using TB-500. - **Research-product identity can vary**: Analytical identification is central to the TB-500 literature because the short fragment can be confused with the parent protein or modified products.[1] - **Banned in sport**: WADA names TB-500 among thymosin beta-4 derivatives prohibited at all times.[7] ## FDA status Not FDA-approved for any use FDA’s page, content current as of April 22, 2026, lists the nomination for the thymosin beta-4 fragment LKKTETQ, identified as TB-500, as withdrawn while retaining a safety note. Withdrawal does not change the other requirements that apply to compounding.[8] TB-500 is not on FDA’s finalized list of additional bulk substances for patient-specific compounding.[9] Before a July 2026 advisory meeting, FDA staff proposed against listing it; FDA had posted no official vote record as of September 17, 2026.[10] Compounded drugs are not FDA-approved.[11] Promise Peptides is currently taking waitlist sign-ups. Joining is not a medical request and no prescription comes from it. ## A prescription route Promise is currently accepting waitlist signups. Joining is not a treatment request and does not result in a prescription. If treatment visits open, any treatment request would require clinical review; prescribing and pharmacy fulfillment would remain separate decisions. 1. **Start on Promise’s TB-500 page**: It shows what the treatment involves and its current availability. 2. **Answer the TB-500 questionnaire**: A licensed provider reviews health history, medicines and goals, and can decline. Not everyone qualifies. 3. **Pharmacy review is a separate step**: A prescription does not guarantee preparation or dispensing. A pharmacy must separately determine whether it can fulfill the prescription under the applicable requirements. A prescription does not make TB-500 FDA-approved or convert full-protein thymosin beta-4 findings into evidence for the fragment; it reflects an individualized clinical decision. TB-500 at Promise Read the treatment information and view the current waitlist. [Join the Promise waitlist](https://mypromise.com/products/tb-500?utm_source=peak&utm_medium=affiliate&utm_campaign=library&utm_content=tb-500) Peak may earn money when readers become Promise patients. Joining does not guarantee future treatment availability. Availability would depend on the treatment, state, clinical review and separate pharmacy review. ## Questions ### What is the relationship between TB-500 and thymosin beta-4? TB-500 is the synthetic acetylated sequence Ac-LKKTETQ, drawn from the actin-binding region of the full 43-amino-acid protein thymosin beta-4.[1] ### Are there human clinical trials on TB-500? The cited human phase 1 study used full-length thymosin beta-4, not TB-500. No controlled human fragment trial is identified here.[5] ### Is TB-500 a steroid? No. It is a synthetic seven-amino-acid peptide fragment. Its chemical structure and anti-doping category are different from anabolic steroids. ## Sources 1. Ho EN, Kwok WH, Lau MY, Wong AS, Wan TS, Lam KK, Schiff PJ, Stewart BD. Doping control analysis of TB-500, a synthetic version of an active region of thymosin beta-4, in equine urine and plasma. *J Chromatogr A*. 2012;1265:57-69. [PubMed 23084823](https://pubmed.ncbi.nlm.nih.gov/23084823/) 2. Irobi E, et al. Structural basis of actin sequestration by thymosin-beta4: implications for WH2 proteins. *EMBO J*. 2004. [PubMed 15329672](https://pubmed.ncbi.nlm.nih.gov/15329672/) 3. Malinda KM, et al. Thymosin beta4 accelerates wound healing. *J Invest Dermatol*. 1999. [PubMed 10469335](https://pubmed.ncbi.nlm.nih.gov/10469335/) 4. Bock-Marquette I, et al. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. *Nature*. 2004. [PubMed 15565145](https://pubmed.ncbi.nlm.nih.gov/15565145/) 5. Ruff D, et al. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. *Ann N Y Acad Sci*. 2010. [PubMed 20536472](https://pubmed.ncbi.nlm.nih.gov/20536472/) 6. Spurney CF, et al. Evaluation of skeletal and cardiac muscle function after chronic administration of thymosin beta-4 in the dystrophin deficient mouse. *PLoS One*. 2010. [PubMed 20126456](https://pubmed.ncbi.nlm.nih.gov/20126456/) 7. World Anti-Doping Agency. [The 2026 Prohibited List](https://www.wada-ama.org/en/prohibited-list) (S2.3). 8. U.S. Food and Drug Administration. [Certain bulk drug substances for use in compounding that may present significant safety risks](https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks). Content current as of April 22, 2026. 9. U.S. Food and Drug Administration. [Bulk drug substances used in compounding under section 503A of the FD&C Act](https://www.fda.gov/drugs/human-drug-compounding/bulk-drug-substances-used-compounding-under-section-503a-fdc-act). 10. U.S. Food and Drug Administration. [July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee](https://www.fda.gov/advisory-committees/advisory-committee-calendar/july-23-24-2026-meeting-pharmacy-compounding-advisory-committee-07232026). 11. U.S. Food and Drug Administration. [Compounding and the FDA: Questions and Answers](https://www.fda.gov/drugs/human-drug-compounding/compounding-and-fda-questions-and-answers). ## Also in the library - [BPC-157](https://peakpeptides.com/peptides/bpc-157/) (Synthetic peptide) - [GLOW](https://peakpeptides.com/peptides/glow/) (Blend) - [KLOW](https://peakpeptides.com/peptides/klow/) (Blend) - [GHK-Cu](https://peakpeptides.com/peptides/ghk-cu/) (Copper tripeptide) --- Peak maps the terrain; it does not examine anyone, so nothing here is medical advice, and the decision about any treatment belongs to a licensed provider who has reviewed your health. Peak may earn money when readers become Promise patients. Peak is not affiliated with any company called Peak Peptides or Peak Performance Peptides.