TB-500

Definition

TB-500 is a synthetic peptide marketed as the active fragment of thymosin beta-4, a 43-amino-acid protein involved in actin regulation and tissue repair; the name attaches to research-market products rather than to any pharmaceutical.

The distinction between full-length thymosin beta-4 and the fragment sold as TB-500 matters, because the published human evidence belongs to the former.

Evidence

Recombinant full-length thymosin beta-4 has completed a first-in-human randomized phase 1 study establishing safety and pharmacokinetics ^[1], and a phase 2 trial reported symptom improvement in severe dry eye ^[2]. The TB-500 fragment as sold has no clinical trial record of its own; buyers read the protein's literature as if it covered the fragment.

That substitution, a studied molecule lending its record to an unstudied cousin, recurs across the research-peptide market.

Lawful access

TB-500 was removed from Category 2 of the interim 503A bulks list in April 2026 without Category 1 listing, and in July 2026 the Pharmacy Compounding Advisory Committee voted 8–6, with one abstention, to recommend adding it to the section 503A list. The vote is advisory; no FDA final rule has issued, and no licensed pharmacy may lawfully compound it as of August 2026.

Related molecules

TB-500 sits in the repair peptides class beside BPC-157, whose PCAC vote it matches, and GHK-Cu, which never reached the agenda; the pending page carries the full July 2026 story.