PeptideDeepDiveWhat Is the TB-500 Peptide? Thymosin Beta-4 Evidence & FDA/WADA Status
The key fact about this tissue-repair research peptide is molecular: TB-500 is a short thymosin beta-4 fragment, while most human research concerns the full-length peptide.
What Is TB-500? The Short Answer
TB-500 commonly refers to Ac-LKKTETQ, a synthetic seven-amino-acid fragment from residues 17–23 of thymosin beta-4 (Tβ4). Full-length Tβ4 is a naturally occurring 43-amino-acid peptide involved in actin regulation and cell movement. Researchers have studied it in skin, corneal, cardiac and wound-healing settings.
However, TB-500 is not an FDA-approved drug. More importantly, it is not the same molecule that generated most of the human evidence used in online TB-500 claims. This guide therefore separates evidence for the fragment from evidence for full-length thymosin beta-4.
TB-500 vs Full-Length Thymosin Beta-4: Read This Carefully
This distinction changes how readers should interpret every claim about “TB-500 clinical trials.” Sellers and articles often use TB-500 and Tβ4 as if they were synonyms, but they describe different molecules.
A synthetic seven-amino-acid fragment, usually identified as Ac-LKKTETQ. FDA says naming and salt forms sold under “TB-500” can vary. The agency found no human exposure data for drug products containing this fragment.
The complete 43-amino-acid peptide. Human studies and registered trials mainly involve this molecule, including topical RGN-137 and ophthalmic RGN-259 formulations.
How Thymosin Beta-4 and TB-500 Are Thought to Work
Full-length thymosin beta-4 binds G-actin, a building block of the cell’s internal framework. Through actin regulation, Tβ4 can influence cell movement and wound-repair processes. Researchers also study links with new blood-vessel formation, inflammation and collagen deposition.
The LKKTETQ region contains an actin-binding motif, and animal research has examined a seven-amino-acid fragment. However, evidence that the marketed Ac-LKKTETQ TB-500 fragment reproduces the full-length peptide’s effects in humans remains absent. Therefore, researchers cannot simply transfer every Tβ4 mechanism or result to TB-500.
What TB-500 and Thymosin Beta-4 Evidence Actually Shows
Animal evidence for full-length Tβ4 is substantial. For example, a 1999 rat study reported 42% greater re-epithelialisation than saline controls at day four and up to 61% at day seven. Another animal study found that the LKKTETQ region promoted repair in aged animals. These findings support further research, but they do not establish a human benefit for commercial TB-500 products.
Human research mainly concerns full-length Tβ4. A first-in-human randomized trial assessed intravenous full-length Tβ4 in healthy volunteers, while registered studies have examined formulations such as RGN-137 for venous stasis ulcers. By contrast, FDA reported in 2026 that it had not identified human exposure data for drug products containing the seven-amino-acid thymosin beta-4 fragment.
In short, readers should not present full-length thymosin beta-4 trials as TB-500 clinical trials. Whether the fragment reproduces the parent peptide’s effects in humans remains unanswered.
How Does TB-500 Compare With BPC-157?
TB-500 and BPC-157 often appear together in recovery-peptide discussions, but the evidence gaps differ. TB-500 is a short Tβ4 fragment whose reputation draws heavily on studies of full-length thymosin beta-4. BPC-157 has a separate preclinical literature, yet it also lacks established human efficacy and safety evidence.
No controlled human study has established the safety or effectiveness of using the two peptides together. For molecule-specific context, read our BPC-157 evidence and legal-status guide. You can also see how both fit into our evidence-led recovery peptide comparison.
TB-500 Regulatory Status, WADA and 503A Compounding
FDA approval: TB-500 is not an FDA-approved drug. FDA also lists the thymosin beta-4 fragment among substances that may present significant safety risks in compounding. The agency cites possible immunogenicity linked to aggregation and peptide-related impurities, along with a lack of identified human exposure data.
503A compounding: In materials prepared for the July 2026 Pharmacy Compounding Advisory Committee meeting, FDA proposed that TB-500 free base and TB-500 acetate should not appear on the 503A Bulks List. Advisory committee input is non-binding, and the official FDA meeting page did not state a final agency determination when this article was updated. Check the FDA source directly because the position can change.
Sport: The 2026 WADA Prohibited List explicitly names thymosin beta-4 and its derivatives, including TB-500. WADA prohibits them at all times for athletes covered by the World Anti-Doping Code.
What Is Still Unknown About TB-500?
- Whether the Ac-LKKTETQ fragment produces clinically meaningful effects in humans.
- The fragment’s absorption, distribution, metabolism and long-term safety in people.
- How product identity, salt form, purity and peptide-related impurities affect risk.
- The safety or effectiveness of combining TB-500 with BPC-157 or other research peptides.
The takeaway: full-length thymosin beta-4 has mechanistic, animal and limited human research behind it. TB-500 is a shorter fragment with some animal evidence but no human exposure data identified by FDA. Treat claims based on full-length Tβ4 trials as indirect evidence, not proof that the TB-500 research peptide works in people.
Frequently Asked Questions About TB-500
Is TB-500 the same as thymosin beta-4?
No. TB-500 commonly refers to the seven-amino-acid Ac-LKKTETQ fragment from residues 17–23 of thymosin beta-4. Full-length Tβ4 contains 43 amino acids, and most human research concerns the full-length molecule.
Is TB-500 approved for human use?
TB-500 is not an FDA-approved drug. FDA says it has not identified human exposure data for drug products containing the thymosin beta-4 fragment and has raised concerns about immunogenicity, aggregation and peptide-related impurities in compounded products.
Is TB-500 allowed in sport?
No for athletes subject to the World Anti-Doping Code. WADA’s 2026 Prohibited List names thymosin beta-4 and its derivatives, including TB-500, as substances prohibited at all times.
What human trials exist for TB-500 or thymosin beta-4?
Human studies and registered clinical trials mainly relate to full-length thymosin beta-4 formulations. FDA reported that it had not identified human exposure data for drug products containing the seven-amino-acid TB-500 fragment.
References
- U.S. Food and Drug Administration (2026). TB-500 free base and TB-500 acetate: 503A Bulks List evaluation.
- U.S. Food and Drug Administration. Certain bulk drug substances for use in compounding may present significant safety risks.
- U.S. Food and Drug Administration (2026). July 23–24 Pharmacy Compounding Advisory Committee meeting.
- World Anti-Doping Agency (2026). 2026 Prohibited List.
- Malinda, K.M. et al. (1999). Thymosin β4 accelerates wound healing. Journal of Investigative Dermatology.
- Philp, D. et al. (2003). The actin binding site on thymosin beta-4 promotes angiogenesis. FASEB Journal.
- Full-length thymosin beta-4 first-in-human study. Randomized clinical trial record on PubMed.
- ClinicalTrials.gov. RGN-137 for venous stasis ulcers (NCT00832091).