Thymulin

What thymulin is

Thymulin is produced by the epithelial cells of the thymus, the organ behind the breastbone in which T cells mature. It was first described as serum thymic factor, in French “Facteur thymique sérique”, FTS for short. In 1982 the group around Dardenne and Bach showed that the peptide is only active with a bound zinc ion and proposed the name thymulin for this active form. In clinical studies the synthetic form was called nonathymulin.

Thymulin is not the same as thymalin, a thymus extract from Russian bioregulator research, nor is it the same as thymosin alpha-1, another thymic peptide with approvals outside Germany.

What is rated is the state of knowledge. As an endogenous hormone, thymulin is well described; as an active substance it has barely been studied: the few studies in humans date from the 1980s.

How it works

Thymulin promotes the maturation and function of T cells. Because it needs zinc, its activity in the blood also reflects zinc status: in people with mild zinc deficiency, thymulin activity was reduced and rose again after zinc supplementation; in an experiment with deliberately induced zinc deficiency, T-cell subsets and IL-2 activity shifted at the same time and normalized with zinc (Prasad 1988).

The level declines with age. In 93 healthy people from birth to age 80, thymulin rose until the age of 5 to 10 years, fell from puberty onward, reached its lowest point at around 36 years and then remained stable until 80 (Consolini 2000). The idea of replacing thymulin to counter immune aging builds on this course.

In 2026 a new mechanism was added: old mice and humans had more inflammation-active macrophages. Thymulin dampened their inflammatory messengers by inhibiting NF-κB and, in old mice, improved tumor control and the response to immunotherapy (Kanemaru 2026). Mice were treated.

What the studies show

Bordigoni 1982: three children with immune deficiency

Three children with IgA and IgE deficiency and a T-cell defect, two of them with ataxia telangiectasia, received synthetic serum thymic factor intravenously (Lancet). Infections became less frequent and milder, tests of cellular immunity improved, IgA appeared for the first time in two children, and vaccine antibodies rose. In two children the improvement regressed after an interruption and returned when the substance was given again. A case series without a control group.

Amor 1987: rheumatoid arthritis

Two randomized, double-blind trials (Ann Rheum Dis) compared three dose levels of nonathymulin with placebo. The middle level performed best: in the overall assessment of all participants, 56 percent improved compared with 17 percent on placebo, p less than 0.02. Side effects were few; no clear changes in immune parameters were seen. The abstract does not state the number of participants; larger follow-up studies were not found.

Roullet 1989: multiple sclerosis

40 people with progressive multiple sclerosis and moderate disability received nonathymulin under the skin or placebo for six months and were observed for a further six months (Acta Neurol Scand). There was no difference in degree of disability, walking ability or functional scale; no notable side effects occurred. The authors concluded that nonathymulin does not work in this disease.

Kanemaru 2026: inflammation in aging, in mice

The paper in Nature Communications links declining thymulin with age-related inflammation: thymulin inhibited the inflammatory switch NF-κB in macrophages, strengthened T-cell defense against tumors in old mice, prolonged survival and made tumors more sensitive to anti-PD-L1 immunotherapy, depending on the age of the animals. An indication of a pathway, not an application in humans.

Where the data stop

• Immune rejuvenation in humans. No one has treated healthy older people with thymulin and measured whether their immune defense becomes younger. The human studies concerned rheumatism, multiple sclerosis and congenital immune defects.
• Hair growth. No study with thymulin was found for hair growth or hair loss.
• From level to replacement. The fact that the thymulin level declines from puberty onward does not mean that supplying it from outside has any effect. The 2026 mouse data describe a pathway, not proof in humans.
• Replication and approval. The signal in rheumatoid arthritis was not confirmed in larger studies, and no approval followed. No study with thymulin as the active substance is registered in the ClinicalTrials.gov registry.

Status, approval and legal

Thymulin is not approved as a medicine in Germany, the EU or the US. The synthetic form nonathymulin was clinically tested in the 1980s; no approval followed. Today thymulin is offered as a research peptide on the gray market.

In sport, as a non-approved substance, it falls under class S0 of the WADA Prohibited List and is prohibited at all times. We do not give dosage information for non-approved substances. What is known about zinc itself is on the page on zinc.

Safety

Safety data in humans exist only from the short studies of the 1980s. In the rheumatism trials the side effects were few; in the MS study no notable ones occurred over six months. Long-term data are missing, as are data on older people, on autoimmune diseases, on the period after a transplant or on ongoing immunotherapies.

Thymulin intervenes in T-cell maturation, and how this plays out in an overactive immune system has not been studied. With gray-market products it is also not assured that purity and content are correct, nor that the peptide is loaded with zinc and is therefore in the active form at all.

Sources

• Dardenne M et al., Proc Natl Acad Sci USA 1982 – only bound zinc makes the serum thymic factor active (thymulin)
• Consolini R et al., Clin Exp Immunol 2000 – thymulin levels in 93 healthy people from birth to age 80
• Prasad AS et al., J Clin Invest 1988 – thymulin in mild zinc deficiency in humans
• Brignola C et al., Aliment Pharmacol Ther 1993 – zinc supplementation raises thymulin in Crohn’s disease, randomized with 27 people
• Bordigoni P et al., Lancet 1982 – synthetic serum thymic factor in three immunodeficient children
• Amor B et al., Ann Rheum Dis 1987 – nonathymulin in rheumatoid arthritis, two placebo-controlled trials
• Roullet E et al., Acta Neurol Scand 1989 – nonathymulin in multiple sclerosis, double-blind pilot study with 40 people
• Kanemaru H et al., Nat Commun 2026 – thymulin, inflammation in aging and cancer immunotherapy (mouse)
• ClinicalTrials.gov – search for thymulin, no study with thymulin as the active substance
• WADA Prohibited List – class S0, non-approved substances