Research material and lot documents
TB-500 side effects have not been established in people. FDA's May 15, 2026 briefing document states that "potential safety risks associated with the use of TB-500 in humans are unknown." Source: FDA briefing document for TB-500, May 15, 2026.
FDA reviewed TB-500 in 2026 as a bulk drug substance proposed for pharmacy compounding, with wound healing as the use under review. The briefing reports these findings:
FDA searched its adverse event reporting database for TB-500 through March 26, 2025. "The FAERS search did not retrieve any reports, and the literature search did not identify any cases of AEs."
FDA did not identify acute toxicity, repeated-exposure toxicity, genotoxicity, developmental and reproductive toxicity or carcinogenicity studies of TB-500.
FDA raised immunogenicity, an immune response to the peptide, as a concern linked to aggregation and peptide-related impurities. It states: "The nominator did not provide, and FDA did not identify clinical studies assessing immunogenicity nor aggregation of TB-500."
Source for the list: FDA briefing document.
Human safety reports exist for thymosin beta-4, the protein of 43 amino acids. A 2010 randomized, placebo-controlled study in healthy volunteers tested synthetic thymosin beta-4 after a single exposure and after repeated exposure. The authors reported that adverse events were infrequent and mild or moderate, and that there were no serious adverse events. Source: 2010 healthy-volunteer study of synthetic thymosin beta-4, PMID 20536472.
The venous ulcer and dry eye trials on the TB-500 benefits page reported acceptable safety and no adverse events, respectively. All of these trials tested the 43-residue protein under trial conditions. None tested TB-500.
FDA's briefing concludes that "TB-500 (free base) is not physically and chemically well characterized." It says that a representative public certificate it reviewed did not cover assay, impurities, bacterial endotoxins or aggregates. Source: FDA briefing document. The TB-500 for sale page sets out the naming and certificate points. For the identity, purity, fill, endotoxin and sterility fields that one supplier describes, see Curo's testing page.
FDA's briefing says there is no applicable United States Pharmacopeia or National Formulary monograph for TB-500 (free base) or its acetate form, "and neither is a component of an FDA-approved drug." FDA's UNII record for TB-500 carries the note "UNII availability does not imply any regulatory review or approval." Sources: FDA briefing document and FDA UNII record for TB-500.
The briefing also states that "TB-500 is not recognized in either the European or Japanese Pharmacopeias." It lists countries, including Canada, Australia and the United Kingdom, in which it found no approved products containing TB-500.
As FDA's briefing describes it, the 503A Bulks List is the list of bulk drug substances that can be used in compounding under section 503A of the Federal Food, Drug, and Cosmetic Act. FDA's records on TB-500 follow this timeline:
April 22, 2026 content date: FDA's page on bulk drug substances that may present significant safety risks lists "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" under the heading "Bulk drug substances nominated but withdrawn". FDA describes that list as substances "previously in category 2 of the interim policies" whose nominators withdrew them. Its text for TB-500 includes: "FDA lacks important information regarding any safety issues raised by this drug". Source: FDA bulk drug substances safety-risk page, content dated April 22, 2026.
May 15, 2026: FDA's briefing document for the committee states that "a balancing of the criteria weighs against TB-500 (free base) and TB-500 acetate being placed on that list." Source: FDA briefing document.
July 23, 2026: the Pharmacy Compounding Advisory Committee discussed TB-500. One FDA presentation slide reads: "FDA is proposing that TB-500 (free base) and TB-500 acetate NOT be included on the 503A Bulks List". Source: FDA presentations, July 23, 2026.
FDA's meeting page, content dated August 6, 2026, lists the briefing documents and the agenda and posts no vote result. The authors of a Health Affairs commentary dated August 4, 2026 reported that six of the seven peptides reviewed, TB-500 among them, received a majority of votes supporting addition to the list. They also noted that the committee's recommendations are advisory and do not determine whether FDA will add the substances to the list. Sources: FDA meeting page for July 23-24, 2026 and Health Affairs commentary, August 4, 2026.
FDA's briefing states: "The FDA will not issue a final determination on the issues at hand until input from the advisory committee process has been considered and all reviews have been finalized."
The Code of Federal Regulations lists the substances on the 503A Bulks List at 21 CFR 216.23(a). The electronic CFR, up to date as of October 13, 2026, names six: Brilliant Blue G, cantharidin, diphenylcyclopropenone, N-acetyl-D-glucosamine, squaric acid dibutyl ester and thymol iodide. TB-500 is not among them. Source: 21 CFR 216.23 on the electronic CFR.
WADA's 2026 Prohibited List, in force since January 1, 2026, names "Thymosin-ß4 and its derivatives e.g. TB-500" in section S2.3, Growth Factors and Growth Factor Modulators. Section S2 is headed "PROHIBITED AT ALL TIMES (IN- AND OUT-OF-COMPETITION)" and states: "All prohibited substances in this class are non-Specified Substances." Source: WADA 2026 Prohibited List.
WADA published the 2027 list on September 21, 2026. It takes effect on January 1, 2027 and keeps the same wording for thymosin-ß4 and TB-500 in S2.3. Sources: WADA announcement of the 2027 list and WADA 2027 Prohibited List.
USADA's advisory on the 2027 list, published October 6, 2026, names TB-500 among peptides that fall under the S0 (Non-Approved Substances) class, "or other classes (such as S2 or S4)." It states that "athletes are strictly liable, meaning they are ultimately responsible for what is in their systems." Source: USADA advisory on the 2027 Prohibited List. In a September 17, 2025 announcement, USADA reported a four-year period of ineligibility in a case in which an athlete "possessed and used BPC-157 and TB-500." Source: USADA sanction announcement, September 17, 2025.
FDA does not draw that conclusion. Its briefing notes that reporting to its database is voluntary and incomplete, and states: "FDA cannot make definitive conclusions regarding the safety of TB-500." Source: FDA briefing document.
FDA "did not identify nonclinical carcinogenicity studies of TB-500 (free base) or TB-500 acetate." The review therefore has no carcinogenicity finding to report. Source: FDA briefing document.
They describe the 43-residue protein. FDA's records list TB-500 under a separate UNII. Source: FDA UNII record for TB-500.
For a supplier-authored article on TB-500 research, legality and price, see Curo's TB-500 article.