TB-500 Sourcing and Purity Risk: What to Do When It Doesn't Go Away

Why there is no expected course

FDA's July 2026 evaluation searched PubMed, Embase, ClinicalTrials.gov and other sources and found no article in which TB-500 was given to a human, and no human pharmacokinetic or pharmacodynamic data by any route [1]. There is no approved dose and no human dosing study [1]. FDA also found no nonclinical toxicity studies of TB-500 and no study of its immunogenicity or aggregation [1]. Animal studies show subcutaneous or intraperitoneal TB-500 reaching the bloodstream and being broken down into smaller peptides; no intramuscular animal studies were found [1].

What is on record about reactions

FDA's adverse-event database search through March 26, 2025 retrieved no TB-500 reports, and its food and supplement complaint system retrieved two cases about blended TB-500 and BPC-157 products, with no safety assessment [1]. FDA found no published case reports [1].

FDA's BPC-157 review describes a 40-year-old woman who used a 'research purposes only' product containing 5 mg BPC-157 and 5 mg TB-500, injected subcutaneously twice daily. Within a week she developed widespread skin hyperpigmentation and gum darkening, and it recurred when she tried the product again two weeks later. Because the product held two peptides, FDA said it cannot tell whether either caused it [2]. The report does not say how long the reaction lasted.

Purity and characterization concerns

FDA's stated concern for injectable TB-500 is immunogenicity, an immune reaction, potentially amplified by peptide aggregation and peptide-related impurities. Its staff briefing described the substance as not well characterized, citing inconsistent naming and a lack of impurity, aggregate and endotoxin data [1].

TB-500 is a synthetic 7-amino-acid, N-acetylated fragment (residues 17 to 23) of the 43-amino-acid protein thymosin beta-4, with a molecular weight of about 889 g/mol. 'TB-500' is a common name rather than an official drug name, and FDA found several salts and derivatives, including different active moieties, sold under it [1]. The marketed product is a research-use-only injectable powder in 2 mg to 15 mg vials, sold alone or blended with BPC-157. FDA found no pharmacy marketing a compounded TB-500 product and no outsourcing facility reporting one [1].

If a reaction has not settled

No recovery timeline exists for TB-500. Useful details to write down are when the reaction began, the vial and lot number, the supplier, whether the product was blended with BPC-157, the dates of each injection, and photographs of any skin change.