Thymulin peptide: the zinc-dependent thymic hormone, what the trials found and what is unknown

Thymulin is one of the few thymic hormones whose structure is fully known. In the early 1970s the Paris group of Jean-François Bach and Mireille Dardenne found a factor in serum that could induce T-cell markers on immature cells and named it facteur thymique sérique, or FTS. In 1977 Pleau and colleagues published its structure after purifying it from pig serum: a nine-amino-acid peptide beginning with pyroglutamate, pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn, and showed that a synthetic peptide with that sequence had the same biological activity as the natural one ^[1]. The name thymulin was adopted later, once it became clear that the peptide is only active when a zinc ion is bound to it ^[2].

Unlike the synthetic Khavinson peptides sold alongside it, such as thymogen and thymalin, thymulin is a real hormone with a wider and more independent literature, produced in France, Argentina, Brazil, Russia, the United States and elsewhere. It is produced exclusively by thymic epithelial cells, and its production falls as the thymus shrinks with age ^[7]. Its closest relative in the research-peptide market is thymosin alpha-1, a longer thymic peptide that is a licensed medicine in some countries; the two are unrelated in sequence.

Research suppliers sell synthetic thymulin peptide as a freeze-dried powder. Whether the product is the thymulin zinc complex, and whether it would be active without the metal, is not usually stated on listings, which matters because the zinc-free peptide is biologically inactive ^[2].

Thymulin’s original described role is in T-cell differentiation. Bach summarised it in 1989 as a metallopeptide that induces the differentiation of T cells and enhances several functions of T-cell subsets in normal or partially thymus-deficient recipients, with its effect on suppressor T cells the most notable ^[2]. Its dependence on zinc is so tight that serum thymulin activity is used as a marker of zinc status: in 1988 Prasad and colleagues showed that mild, experimentally induced zinc deficiency in human volunteers lowered serum thymulin activity and altered T-cell subsets, and that both were corrected by zinc repletion ^[3]. In patients with Crohn’s disease in remission, three months of 200 mg per day of zinc sulphate restored low plasma thymulin, whereas 60 mg per day did not ^[14]. A 2021 rat study found serum thymulin activity fell 61 per cent on a low-zinc diet, making it more sensitive to zinc restriction than serum zinc itself ^[20].

The second strand of research treats thymulin as a link between the thymus and the pituitary. Reviews by Goya and Reggiani in Argentina describe thymulin as a hypophysiotropic peptide whose production is controlled by hormones and which in turn influences pituitary hormone release ^{[15] [7]}. In cultured rat pituitary cells, thymulin stimulated release of luteinising hormone and follicle-stimulating hormone in a dose- and receptor-dependent way, with a synergistic effect alongside gonadotropin-releasing hormone ^[17]. In congenitally athymic nude mice, which lack thymulin, a neonatal gene therapy that restored circulating thymulin prevented the loss of GnRH neurons and gonadotropic cells and rescued premature ovarian failure ^[13].

The third strand, and the one most relevant to current interest, is anti-inflammatory. Dardenne’s group and collaborators in Lebanon showed that thymulin has two-sided effects on pain: at nanogram doses injected locally it causes hyperalgesia through prostaglandin E2, whereas systemic doses of 1 to 25 µg of thymulin, or of a synthetic analogue called PAT that lacks the hyperalgesic effect, reduced the inflammatory pain, cytokine rise, fever and sickness behaviour caused by endotoxin ^[6]. A 2010 review in lung disease models concluded that thymulin broadly inhibits pro-inflammatory cytokines, suppresses p38 MAPK and blocks NF-κB activation ^[8].

The 2026 Nature Communications paper from the University of Southern California pulled these threads together in ageing. Using heterochronic parabiosis and bone marrow chimeras, the authors found that inflammatory myeloid cells that accumulate with age are suppressed by circulating factors in young hosts, identified thymulin as one such factor that declines with age, and showed that it suppresses IL-1, IL-6 and TNF-α production by inhibiting NF-κB. In mice, thymulin enhanced antitumour T-cell immunity and sensitised tumours to anti-PD-L1 therapy in an age-dependent manner ^[9].

Most search interest in thymulin benefits concerns inflammation, immunity, ageing and, more recently, cancer immunotherapy. The animal evidence is broader than for any Khavinson peptide, but nearly all of it uses thymulin given by injection or expressed from a gene, not the reconstituted powder a research buyer receives.

Inflammation and sepsis: Russian researchers in Pushchino reported in 2018 that thymulin, free or bound to polybutylcyanoacrylate nanoparticles, reduced fever, lymphocyte apoptosis, cytokine production and NF-κB and MAPK signalling in mice given escalating doses of endotoxin to model chronic septic inflammation, and partly restored brain serotonin and melatonin ^[10]. The same group found nanoparticle-bound thymulin reduced symptoms and cytokine levels in a relapsing-remitting model of multiple sclerosis in mice ^[18]. In rats with adjuvant-induced arthritis, 21 days of intraperitoneal thymulin reduced thermal hyperalgesia and paw swelling, and reduced spinal microglial activation, p38 MAPK phosphorylation and TNF-α and IL-6 ^[12]. A 1997 Japanese study found thymulin reduced paw swelling, anti-collagen antibodies and joint damage in collagen-induced arthritis in rats ^[16].

Asthma: a Johns Hopkins and Rio de Janeiro collaboration published in Science Advances in 2020 showed that a single intratracheal dose of nanoparticles carrying a thymulin analogue gene, given after allergic asthma was fully established in mice, normalised chronic inflammation, fibrosis and lung mechanics within 20 days ^[11]. This was gene therapy, not peptide injection.

Ageing and cancer: the 2026 Nature Communications study found that thymulin restrains age-associated myeloid inflammation and improved tumour control and survival in aged mice, including with anti-PD-L1 therapy ^[9]. It is a mouse study with human tissue analyses, and it explicitly presents thymulin as a candidate strategy rather than a treatment.

Reproduction and endocrine function: the Argentine gene-therapy series showed that restoring thymulin in athymic mice prevented reproductive and pituitary abnormalities ^{[13] [7]}. Human data are limited to associations: in 290 Nepalese children, thymulin concentrations, used as a proxy for thymic function, averaged 1.37 ng/mL and tracked nutritional status and season ^[19].

Thymulin was tested in people in the 1980s under the name nonathymulin, a synthetic version of the serum thymic factor. In rheumatoid arthritis, Amor and colleagues ran two randomised, double-blind, placebo-controlled trials comparing 1, 5 and 10 mg per day. The 5 mg dose was the most effective, with 56 per cent of patients improved on global assessment against 17 per cent with placebo and improvement on four objective measures, with minimal adverse effects and no clear change in immune parameters ^[4].

In multiple sclerosis, a randomised, double-blind, placebo-controlled trial of 40 patients with progressive disease and moderate disability gave subcutaneous nonathymulin or placebo for six months and followed them for six more. There was no difference in disability scores, ambulation index or functional scale, and no significant side effects were recorded ^[5].

Human observational data are more plentiful and concern the body’s own thymulin rather than treatment. Serum thymulin falls in zinc deficiency and recovers with zinc ^{[3] [14]}, and it is used in nutrition research as a marker of thymic function in children ^[19]. The 2026 cancer immunology paper analysed human myeloid cells and tissue but did not give thymulin to people ^[9].

No thymulin trial is currently listed on ClinicalTrials.gov, and the only registered entry mentioning it concerns zinc supplementation and vaccine response in infants, where thymulin was a biomarker. The clinical trials status of thymulin as of September 2026 is therefore: two 1980s double-blind trials, one positive in rheumatoid arthritis and one negative in multiple sclerosis, and no modern trial of the peptide for any use.

In the rheumatoid arthritis trials, patients were assessed over the trial period after daily injections, and in the multiple sclerosis trial, six months of treatment produced no difference ^{[4] [5]}. In rat arthritis, effects on pain and swelling were measured across 21 days of daily dosing ^[12], and in the asthma gene-therapy study, lung pathology was normalised 20 days after a single dose ^[11]. None of these figures applies to research-grade thymulin bought online, for which no human timeline exists.

In the 1980s human trials, nonathymulin was given by daily injection at 1, 5 or 10 mg, with 5 mg the most effective in rheumatoid arthritis ^[4]; the dose in the multiple sclerosis trial was given subcutaneously for six months ^[5]. These are the only published human doses and they are not recommendations.

Animal doses are far lower and are given per animal or per kilogram. Systemic doses of 1 to 25 µg per mouse or rat reduced endotoxin-induced inflammation, while nanogram amounts injected locally caused hyperalgesia, a reminder that dose and route change the direction of the effect ^[6]. Rat arthritis studies used repeated intraperitoneal injections over three weeks ^[12], and the sepsis and multiple sclerosis studies used free thymulin or a nanoparticle formulation designed to prolong its presence in the blood ^{[10] [18]}. The 2026 cancer study gave thymulin to aged mice as a peptide and also examined its endogenous levels ^[9].

Because activity depends on zinc, a dose figure for synthetic thymulin without zinc may be meaningless ^[2]. Suppliers typically sell 10 mg vials; to convert vial contents to a concentration, use the thymulin calculator or the general peptide calculator.

Every human study gave thymulin by injection ^{[4] [5]}. Animal studies have used intraperitoneal, subcutaneous, local intraplantar and intracerebroventricular injection, nanoparticle-bound peptide and inhaled or intramuscular gene therapy ^{[6] [10] [11] [13]}. There are no published data on oral or nasal thymulin in people. Research suppliers sell the peptide as a lyophilised powder for reconstitution with bacteriostatic water; listings do not usually state whether the product is the zinc complex.

In the two double-blind trials, adverse effects were described as minimal in rheumatoid arthritis ^[4] and no significant side effects were recorded over six months in multiple sclerosis ^[5]. Bach wrote in 1989 that the peptide is not toxic ^[2], and the 2010 lung review said it showed no toxicity even at high doses in animals ^[8].

Two findings deserve attention. First, at low local doses thymulin is pro-inflammatory and causes pain through prostaglandin E2, so its effect is not simply anti-inflammatory ^[6]. Second, thymulin stimulates pituitary gonadotropin release in cell and animal studies ^{[17] [13]}, so an endocrine effect in people cannot be ruled out. There are no data on long-term use, on use with immunosuppressants or immunotherapies, on pregnancy, or on the research-grade product, and the 2026 finding that thymulin alters antitumour immunity in an age-dependent way ^[9] is a reason for caution, not a reason to use it.

Thymulin is not an approved medicine and its safety has not been assessed by any regulator. We have not seen it named on the FDA’s compounding lists or on the WADA Prohibited List. For rules on possession and sale, see our legal status overview.

Thymulin has never been approved as a medicine in any country we are aware of. Its clinical development as nonathymulin stopped after the 1980s trials ^{[4] [5]}, and current work is preclinical, including gene-therapy approaches that would not involve the peptide itself ^{[11] [7]}. Products sold as thymulin by research suppliers are unlicensed and labelled for laboratory use.

See the UK, US, Canada and Australia pages for what that means in practice, and our guide to what research peptides are.

Thymulin is supplied as a freeze-dried powder and is generally stored refrigerated, dry and away from light, with reconstituted solutions kept cold and used within a limited period. Because biological activity depends on zinc binding, buffers or additives that chelate metals could in principle inactivate it ^[2]. See how to store peptides for general guidance.

Thymulin is a nine-residue peptide with a pyroglutamate at one end, and a certificate of analysis should show a measured mass close to 859 g/mol and purity by HPLC; a product missing the pyroglutamate or supplied as a different salt would show a different mass. Learn how to read a peptide COA and what third-party testing covers, and ask the seller whether the product is the zinc complex.

Compare thymulin prices across suppliers, including listings in the UK and US, and see our list of third-party tested suppliers. Thymulin is sometimes marketed next to the Khavinson peptides thymogen, vilon and epitalon as an immune or anti-ageing peptide; it is a different kind of molecule with a different evidence base, and none of the four has human evidence for anti-ageing use. Our guide to spotting a fake peptide supplier covers the warning signs.