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.

The two records were counted separately in August 2026 and they are not the same size. Searched on its own names, TB-500 returns 31 indexed papers against 1,107 for the full-length protein, and 21 of the 31 carry the Humans subject heading ^[5]. Under the clinical-trial publication type the protein returns 8 records and 7 under the stricter randomized-controlled-trial type; TB-500 returns one record under the clinical-trial type and zero randomized trials, and that single record was read rather than counted — it is a regression analysis of tuberculosis incidence in respiratory patients, matched on the letters TB and unrelated to the peptide ^[5].

What the 21 human-tagged TB-500 records mostly contain is analytical chemistry written for sport drug testing rather than therapy. A 2012 paper synthesized and identified the substance present in a TB-500 formulation as the N-terminal acetylated 17-23 fragment of thymosin beta-4, the sequence Ac-LKKTETQ — seven residues of a 43-residue protein — and proposed a method for detecting it in plasma and urine ^[3]. A 2023 laboratory analysis of products sold under the TB500 and TB1000 names reported that their contents were not consistently what the labels described ^[4].

A first trial of the fragment itself is now registered. ClinicalTrials.gov lists a randomized, placebo-controlled phase 1/2 study of the thymosin beta-4 17-23 fragment in adults with stable atherosclerotic cardiovascular disease, recruiting since February 2026 with completion estimated for 2028; it has posted no results as of September 2026 ^[9].

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 to recommend adding it to the section 503A list. The margin is reported as 8–6 with one abstention by McDermott Will & Schulte and by LumaLex Law, whose separate accounts of the meeting agree substance by substance ^{[6, 7]}; the FDA has published no minutes, transcript or vote summary, so the figure is secondary and this page says so wherever it appears. The vote is advisory; no FDA final rule has issued, and no licensed pharmacy may lawfully compound it as of August 2026.

FDA's statement of its safety concerns remains the one on its safety-risk page: compounded drugs containing the fragment may pose a risk of immunogenicity for certain routes because of the potential for aggregation and peptide-related impurities, FDA has not identified any human exposure data on drug products containing it, and the agency lacks important information on whether it would cause harm if given to humans ^[8].

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. ARA-290 is in the same class and holds the opposite evidentiary position: randomized trials in patients, and a Category 3 file that reflects its nomination rather than its literature. TB-500 is also sold inside injectable blends with GHK-Cu and BPC-157; the review of GLOW and KLOW blends sets out what those combinations have and have not been tested for, and the review of the BPC-157 and TB-500 stack, sold as the Wolverine stack, does the same for the two-peptide pairing.

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