Thymulin

Last Updated: August 2026

Thymulin (formerly FTS, Facteur Thymique Sérique / serum thymic factor) is a nonapeptide hormone produced by thymic epithelial cells, first described by Jean-François Bach in 19771 source. Its defining feature is zinc dependence — the peptide binds zinc in a 1:1 ratio to form the biologically active metallopeptide. It is researched for T-cell differentiation and immune modulation, is not approved for any use, and is supplied strictly for research use only. Thymulin sits in Peptigrity's immune support and longevity peptides category.

What is Thymulin and why does zinc dependence matter?

Thymulin is the only true thymic hormone — a single defined nonapeptide, as opposed to a peptide mixture — and it is inactive without zinc, which is what distinguishes it from other thymic peptides. Zinc binding induces the specific three-dimensional conformation required for its activity and antigenicity. This sets it apart from Thymalin (a polypeptide extract mixture) and Thymosin Alpha-1 (a 28-amino-acid peptide) — all thymus-derived, but structurally distinct.

What does the research on Thymulin show?

Thymulin is one of the better-characterized thymic hormones in immunology, with preclinical and some clinical-exploratory work showing it induces intra- and extra-thymic T-cell differentiation and modulates T-cell subset balance and cytokines. Serum thymulin declines markedly with age and with zinc deficiency, correlating with immunosenescence. Evidence level: Preclinical, with older clinical-exploratory data; not an approved therapy.

What are the known side effects and safety concerns?

Early characterization described the natural hormone as non-toxic, but there is no modern controlled human safety trial establishing a safe research-market dose, and activity is entirely contingent on zinc status. The absence of comprehensive human data is the primary consideration. Evidence level: Limited human data. See the legal status guide.

Why does vendor verification matter, and how does Peptigrity verify?

Thymulin is easily conflated with other thymic products (Thymalin, Thymosin Alpha-1) that differ entirely in structure, so mass-spec identity (expected MW ~858.9 Da) and HPLC purity are the objective checks a buyer needs. Peptigrity collects independent third-party Certificates of Analysis for Thymulin from shops' official channels and verifies each for authenticity before publishing. Because shops choose which COAs to publish, results reflect the batches shops have made public rather than every production batch — a selection bias we state openly. A community-funded Testing Grant to purchase and test vials anonymously is in development. Tests come from independent labs such as Janoshik Analytical, Freedom Diagnostics, and Chromate; the trust score weights lab purity and reviews equally (50/50). See how to read lab results. Compare vendors against the independent Thymulin lab tests on file.

This section is for educational and informational purposes only and does not constitute medical advice. Thymulin is not approved by the FDA or equivalent regulators for human use. Always consult a qualified healthcare provider before using any peptide or research compound. Peptigrity is an independent review platform and does not sell, endorse, or recommend specific products or vendors.