Thymulin

A zinc-dependent nonapeptide hormone secreted by thymic epithelial cells, studied since the 1970s for T-cell differentiation, neuroendocrine signaling, and anti-inflammatory effects, mostly in animal models and older human immunology research.

Also referenced as: Serum thymic factor, FTS, Facteur thymique serique, FTS-Zn, Zinc-thymulin, Nonathymulin, Thymic factor

Also appears in: Anti-aging

What is Thymulin?

Thymulin is a nine-amino-acid peptide hormone (pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn) secreted by epithelial cells of the thymus. Bach and Dardenne described the circulating factor in the early 1970s as facteur thymique sérique (serum thymic factor, FTS) and published its biochemical characterization and sequence in 1977. It is biologically active only as a 1:1 complex with zinc; the metal-free peptide is inactive, and the name “thymulin” was proposed in 1982 specifically for the zinc-bound form (FTS-Zn). It appears in the research-peptide market because it is a thymus-derived immune and neuroendocrine signal whose circulating levels fall with age, and because rodent studies have reported anti-inflammatory and analgesic activity for the peptide and a synthetic analog.

How it works

• Zinc is required for activity — treating natural or synthetic FTS with a metal chelator abolishes its activity in a rosette assay, and adding zinc salts at a 1:1 metal-to-peptide ratio restores it; NMR work shows the zinc-bound form adopts a defined conformation while the apo-peptide is flexible (Dardenne et al., Proceedings of the National Academy of Sciences, 1982; Laussac et al., Molecular and Chemical Neuropathology, 1990)
• T-cell differentiation and zinc status — serum thymulin activity falls in mild human zinc deficiency even when plasma zinc is normal and is corrected by zinc repletion in vivo or in vitro, alongside reversible shifts in T-cell subsets and interleukin-2 activity; the authors proposed it as a sensitive indicator of zinc deficiency (Prasad et al., Journal of Clinical Investigation, 1988)
• Neuroendocrine signaling — thymulin secretion is regulated by pituitary hormones and glucocorticoids, and the peptide in turn acts as a hypophysiotropic signal; neonatal adenovector delivery of a thymulin analog (metFTS) to congenitally athymic (nude) female mice restored serum thymulin, prevented the loss of GnRH neurons and pituitary gonadotrophs, and rescued their premature ovarian failure (Reggiani et al., Endocrinology, 2012; Reggiani et al., Current Pharmaceutical Design, 2014)
• Anti-inflammatory and nociceptive effects — in rats the native peptide is biphasic: nanogram doses induce hyperalgesia through prostaglandin E2 and pro-inflammatory cytokines (Safieh-Garabedian et al., Brain, Behavior, and Immunity, 1997; Neuropharmacology, 2000), while higher doses reduce endotoxin-induced hyperalgesia (Safieh-Garabedian et al., Brain Research, 1996; Neuroscience, 2003) and the analog PAT (peptide analogue of thymulin) lowers IL-1β, IL-6, TNF-α, and NGF (Safieh-Garabedian et al., British Journal of Pharmacology, 2002); a 2026 mouse study attributed suppression of age-associated myeloid inflammation to NF-κB inhibition (Kanemaru et al., Nature Communications, 2026)

Research status

Thymulin has a long preclinical history but only a thin and dated human therapeutic record.

• Human trials (1980s): Amor et al. (1987) reported two randomized, double-blind, placebo-controlled trials of synthetic nonathymulin in rheumatoid arthritis comparing 1, 5, and 10 mg/day; the 5 mg arm showed significant clinical improvement on global assessment (56% versus 17% on placebo, p < 0.02) with minimal adverse effects but no clear change in immunologic parameters (Annals of the Rheumatic Diseases, 46(7):549–554). No confirmatory program followed. Santen Pharmaceutical in Japan published a collagen-induced arthritis rat study (Aono et al., Journal of Rheumatology, 1997), but no approved product resulted in Japan or elsewhere.
• Human observational data: thymulin activity has been used as a biomarker rather than a treatment, including in zinc deficiency (Prasad et al., Journal of Clinical Investigation, 1988; DiSilvestro et al., Biological Trace Element Research, 2021) and anorexia nervosa (Wade et al., American Journal of Clinical Nutrition, 1985).
• Animal pharmacology: the Beirut/Paris group’s rat studies on hyperalgesia, c-fos induction in the spinal cord, and the analog PAT in peripheral and intracerebral inflammation (Saadé et al., Journal of Neuroimmunology, 1999; Safieh-Garabedian et al., Neuropharmacology, 2011); thymulin gene therapy in nude mice (Reggiani et al., 2012) and in a nanoparticle asthma model (da Silva et al., Science Advances, 2020); protective effects in streptozotocin diabetes and relapsing-remitting experimental autoimmune encephalomyelitis in mice (Novoselova et al., International Journal of Immunopathology and Pharmacology, 2021; Lunin et al., Archives of Biochemistry and Biophysics, 2023); and the 2026 Nature Communications report that thymulin improved tumor control and sensitized aged mice to anti-PD-L1 therapy (Kanemaru et al., 2026).
• Registry status: no interventional trial of thymulin as a drug is registered on ClinicalTrials.gov as of October 2026; the only record mentioning it (NCT01229579) is a zinc-supplementation study in infants that measured thymulin as a biomarker. There is no FDA-approved or otherwise marketed thymulin drug product.

Common dosage forms

Research vendors sell thymulin as lyophilized powder in vials for reconstitution, most often labeled 10 mg or 20 mg per vial (smaller 1–5 mg vials also appear) and marked for research use only. Some listings specify “zinc-thymulin” or FTS-Zn; others list the peptide acetate without stating whether zinc is complexed. Analytical-grade thymulin acetate is also sold by chemical reagent suppliers. No pharmaceutical formulation exists.

Key considerations

• Regulatory status: no approval in the US or any other market and no active human clinical development; the 1980s rheumatoid arthritis trials were never followed up, no complete response letter or withdrawal exists because nothing was ever filed, and FDA has not placed it on a compounding pathway. The Research Market status reflects that absence of US approval and of any development aimed at approval
• Zinc form matters: biological activity depends on the zinc complex, and research-market labels do not always state which form is supplied, which complicates comparison with the published literature
• Evidence gap: the human efficacy record is a single 1987 paper in rheumatoid arthritis; nearly all modern data come from rodents, often using gene therapy or the analog PAT rather than the native peptide, and the 2026 cancer-immunotherapy findings are preclinical
• Biphasic dose response in rats: low doses of the native peptide induced hyperalgesia and spinal c-fos expression while higher doses were anti-inflammatory; the clinical relevance of this is unknown
• Naming confusion: thymulin (a defined nonapeptide), thymalin (a bovine thymus extract of mixed peptides), and thymosin alpha-1 (a 28-amino-acid peptide approved in some countries outside the US) are distinct compounds; “FTS,” “serum thymic factor,” and “nonathymulin” all refer to thymulin