What Is TB-500?

What Kind of Peptide Is TB-500?

Sellers market TB-500 as a synthetic peptide fragment of thymosin beta-4 (Tβ4). Tβ4 is a small protein that occurs naturally in nearly every human and animal cell. Researchers describe TB-500 free base as a seven-amino-acid sequence with an acetylated N-terminus: Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH, often shortened to LKKTETQ. This sequence corresponds to amino acids 17 through 23 of the full 43-amino-acid Tβ4 protein.

Importantly, “TB-500” is a common market name, not a United States Adopted Name (USAN) or a designation any regulator assigns. In practice, this means the label carries no guaranteed chemical standard. Moreover, FDA’s own 2026 review found that TB-500 free base and TB-500 acetate lack proper physical and chemical characterization. Specifically, the agency cited inconsistent naming conventions across INN, USAN and IUPAC systems, plus missing characterization data for each form.

What Is TB-500’s Proposed Mechanism of Action?

Researchers study TB-500 mainly for its interaction with actin. Actin is a protein that forms part of a cell’s internal skeleton and drives cell movement. By binding and regulating actin, the fragment may influence how readily cells migrate toward an injury site. This proposed pathway forms the biological reasoning behind its “wound healing” reputation.

Actin dynamics also relate to blood vessel formation and inflammatory signalling. Because of this, preclinical papers have additionally explored TB-500 in models of angiogenesis and inflammation. However, a plausible cell-biology pathway differs from a demonstrated clinical benefit. In fact, FDA’s review found that the nomination included no data showing this mechanism translates into an effective treatment.

Does TB-500 Actually Have Human Trial Evidence?

Essentially no. FDA’s 2026 briefing document reported one key finding. Researchers found no medical literature in which anyone administered TB-500 to patients, for wound healing or any other condition. Notably, the agency also identified an in-vitro study that tested TB-500 free base at 50 µg/mL. That study did not show wound healing in scratch-wounded fibroblast cultures. This negative result came from the exact assay type most relevant to how vendors market TB-500.

Separately, FDA also found no evidence that any pharmacy compounded TB-500-related substances. This gap exists despite online interest in the compound dating back to around 2010. As a result, the agency judged the available data too limited to characterize even historical compounding use, let alone establish effectiveness.

TB-500 vs Full-Length Thymosin Beta-4: Why the Distinction Matters

Full-length thymosin beta-4 is a different, larger molecule with its own separate research track. For example, researchers know a synthetic version of full-length Tβ4 as RGN-259. That version has progressed through human clinical trials under an FDA Investigational New Drug application. Specifically, researchers have studied it for an ophthalmic indication, including conditions like dry eye disease and neurotrophic keratopathy. However, that program has not resulted in FDA approval for any indication. Critically, its findings apply to the 43-amino-acid full-length protein — not the seven-amino-acid TB-500 fragment that vendors sell online.

Consequently, researchers cannot automatically attribute laboratory or clinical findings on full-length thymosin beta-4 to TB-500. Sequence connects the two compounds; evidence does not. Overall, marketing material commonly blurs this exact distinction.

What Are the Main TB-500 Safety and Product-Quality Concerns?

FDA’s review cited a lack of both clinical and nonclinical safety information. In fact, the agency described itself as “particularly concerned” about one gap in particular: the complete absence of human safety data by any route. Vendors typically propose TB-500 for intramuscular or subcutaneous injection. Because of this, the agency flagged meaningful potential for immunogenicity, an immune reaction that aggregation and peptide-related impurities could amplify. Notably, the nomination did not include data addressing this risk.

In addition, identity and purity remain open questions. FDA noted that researchers report the free base and acetate forms as stable under specific frozen storage conditions. Still, the quality data needed to confirm identity and purity for each form remained incomplete. Therefore, a “research use only” label does not prove much. Neither does a vendor certificate of analysis. Specifically, neither one establishes that a given product matches the sequence FDA reviewed, let alone that it is safe.

TB-500 Regulatory and WADA Status: Briefly

The FDA has not approved TB-500. In September 2023, the agency placed it into Category 2 of its interim 503A bulk drug substance policy. That same category also caught BPC-157 and several other peptides. This category means compounding pharmacies cannot legally use the substance. Following a 2024 settlement over that process, the nominator withdrew TB-500’s original nomination. As a result, FDA removed it from Category 2 on April 15, 2026. The agency then scheduled it for review by the Pharmacy Compounding Advisory Committee (PCAC).

At the PCAC’s July 23–24, 2026 meeting, FDA staff formally proposed something specific. They proposed keeping TB-500 free base and TB-500 acetate off the Section 503A Bulks List. Specifically, staff cited the effectiveness, safety and characterization gaps this guide describes above. However, sources reported that the advisory committee’s subsequent vote actually recommended inclusion. That outcome would mirror the split recommendation FDA staff and the committee reached on BPC-157 the same week. Either way, that vote remains advisory and non-binding. Therefore, FDA must still take further action. As of this writing, the agency had not published a final decision.

For athletes, the position is more settled. Specifically, the 2026 World Anti-Doping Agency Prohibited List covers thymosin beta-4 and its derivatives, including TB-500, under S0 Non-Approved Substances. As a result, WADA prohibits it at all times. For the fuller country-by-country and FDA timeline, read our TB-500 legal status and evidence guide.

What Is Still Unknown About TB-500?

• Whether TB-500 improves wound healing or recovery outcomes in any well-controlled human trial
• Whether findings on full-length thymosin beta-4 have any relevance to the shorter TB-500 fragment
• A validated human dose, route, formulation or treatment duration
• Long-term immunogenicity, immune and organ-safety effects in people
• Whether products that carry the “TB-500” name share the same chemical structure and purity across vendors
• Whether the Pharmacy Compounding Advisory Committee’s recommendation will change the FDA’s final 503A decision

The takeaway: TB-500 is a synthetic thymosin beta-4 fragment with a plausible cell-biology mechanism. Still, it has essentially no direct human evidence, and the one relevant lab test on record found no wound-healing effect. Its regulatory status also remains unresolved pending FDA’s final 503A decision. Finally, to place it within the wider category, see how TB-500 compares with BPC-157, GHK-Cu, KPV and MOTS-c.

Frequently Asked Questions About TB-500