TB-500 and Liver Function: What the Evidence Actually Shows

Does TB-500 affect liver enzymes?

FDA's review found no human ALT, AST, bilirubin or fibrosis data for TB-500, and no nonclinical toxicity studies [1]. Whether it injures or protects the liver is therefore unknown. For general context, the ACG guideline describes drug-induced liver injury as a diagnosis of exclusion that requires a thorough work-up for competing causes [6].

What TB-500 is

TB-500 is not the full protein. It is the N-acetylated 7-amino-acid piece spanning residues 17 to 23 (Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln), about 889 g/mol, of the 43-amino-acid protein thymosin beta-4 [1]. 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 nomination FDA reviewed describes the LKKTETQ stretch as the actin-binding site behind the parent protein's wound-healing effects [1]. That is a proposed mechanism for thymosin beta-4 and says nothing about the liver. FDA's stated safety concern for injectable TB-500 is immunogenicity, potentially amplified by peptide aggregation and peptide-related impurities [1].

Thymosin beta-4 trials are not TB-500 trials

Full-length recombinant thymosin beta-4 is a different molecule from the fragment. In a phase 1 trial, 54 healthy volunteers received a single intravenous dose of recombinant human thymosin beta-4 (NL005) or placebo at 0.05 to 25 micrograms/kg, and 30 others received 0.5, 2 or 5 micrograms/kg daily for 10 days; adverse events were mild to moderate, with no dose-limiting toxicity and no serious adverse events [7]. Those results describe the parent protein and do not transfer to TB-500.

A human case report involving a TB-500 blend

FDA's separate BPC-157 review describes a 40-year-old woman who injected a research-purposes-only product containing 5 mg BPC-157 plus 5 mg TB-500 subcutaneously twice daily and developed widespread skin hyperpigmentation and gum darkening within a week; the reaction recurred when she tried the product again two weeks later [8]. Because the product held two peptides, FDA said it cannot tell whether either one caused the reaction [8]. The report concerns skin and gums, not liver function.

Regulatory status, in plain terms

TB-500 is not an FDA-approved drug. FDA found no approved product in Canada, Australia, the UK, or the European countries it reviewed, and none authorized by the European Medicines Agency [1]. It appears on none of FDA's reviewed compounding lists [2][3][4], and FDA found no pharmacy marketing a compounded TB-500 product [1].

A draft HHS policy filed October 28, 2026 covers TB-500 acetate given by subcutaneous or intramuscular injection. It says HHS does not intend to take enforcement action against a state-licensed pharmacy, federal facility or licensed physician compounding with it when the policy's conditions are met; the notice states it is not binding, establishes no rights, and is not an approval [5][9]. Compounded drugs are not FDA-approved, and FDA does not review their safety, effectiveness or quality before marketing [5].