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Thymulin

Also known as Facteur Thymique Sérique, FTS, Zn-thymulin, Serum Thymic Factor

Zinc-dependent nine-amino-acid thymic hormone; well-described physiology, almost no modern clinical research.

preclinical Immune & longevity research chemical

At a glance

Category
Immune & longevity
Status
research chemical
Route
subcutaneous or intramuscular in research settings
Half-life
very short; on the order of minutes in plasma
Onset
unknown — no reliable clinical data
Molecular weight
approximately 858.9 g/mol (peptide without zinc)
Sequence
pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn (nonapeptide, biologically active only in complex with Zn2+, in an equimolar ratio)

Not registered as a medicine anywhere. Thymulin has been studied extensively as an endogenous hormone and as a laboratory marker of zinc status 12, but no pharmaceutical development was pursued. What is sold online as 'thymulin' is a research chemical without pharmaceutical quality control.

Doping status: Not listed by WADA

Checked against the WADA 2026 Prohibited List. For a specific product and country, Global DRO is the lookup athletes are expected to use — the List names substances, not brand names.

Mechanism of action

Thymulin is produced by thymic epithelial cells and is the only known thymic hormone whose biological activity depends entirely on an equimolar bound zinc ion. Without zinc the peptide does not adopt the correct spatial conformation and is inactive — which is why measured thymulin activity falls in zinc deficiency and recovers after zinc supplementation 12.

Functionally, thymulin induces the differentiation of immature T cells, both inside and outside the thymus, and influences the function of various T cell subsets, including cytotoxic T cells and NK cells. No specific thymulin receptor has been identified; the exact target on the T cell is unknown.

A neuroendocrine role has also been described: thymulin interacts with the hypothalamic-pituitary axis, and antinociceptive and anti-inflammatory effects via inhibition of pro-inflammatory cytokines have been reported in animal models.

The plasma concentration of thymulin falls sharply with age, in parallel with involution of the thymus. That is the basis for the theoretical assumption that supplementation might counter immune ageing — an assumption that has not been tested in humans.

What the research shows

Thymulin is physiologically well described but therapeutically almost unexplored. The clinical literature consists of a few small, old studies in children with immunodeficiency 4; these have not been replicated in more than forty years. Virtually all current evidence comes from cell culture and animal models. For use as an immune booster or anti-ageing agent in healthy adults there is no clinical evidence.

Research in humans

There are no modern randomised trials. From the 1980s there are small, uncontrolled series in which synthetic FTS was administered to children with primary immunodeficiency, with reported improvement in cellular immunity and IgA production. The most-cited of these is Bordigoni and colleagues (Lancet, 1982), who gave intravenous synthetic FTS to three children — two related patients with ataxia telangiectasia and one with common variable immunodeficiency — and reported improved cell-mediated immunity tests, the appearance of serum IgA within four weeks in two children who had none, and regression of the improvement when dosing was briefly interrupted 4. Three children, no control group, no blinding. By far the greater part of human research is observational and concerns measured thymulin activity as a biomarker — for example in zinc deficiency, old age or malnutrition — not administration 12. There are no published placebo-controlled studies of thymulin supplementation in adults.

Animal and lab research

In mouse and rat models thymulin restores T cell function after thymectomy or ageing, and — in work from groups independent of the original discoverers — anti-inflammatory and analgesic effects have been demonstrated: a thymulin-related peptide reduced inflammatory pain and inflammation in rats, with a potency the authors compared to dexamethasone and indomethacin 5, a thymulin analogue reduced neuropathic pain behaviour after nerve injury 6, and inhaled thymulin gene therapy reversed key pathology in a model of experimental allergic asthma 7. The doses, routes of administration and timescales in these studies do not translate straightforwardly to humans.

Caveats. The only human intervention data are decades old, unblinded, in very small numbers — three children in the principal report — and in a very specific patient group 4. Because of the extremely short half-life it is unclear how an injection could ever produce a sustained effect. The zinc dependence moreover means the effect can disappear entirely with suboptimal zinc status 12, something user protocols rarely take into account. There is no modern safety dossier at all.

What it is used for

  • Research into T cell differentiation and immune ageing (primarily a laboratory application) 12
  • Measurement of thymulin activity as a sensitive indicator of zinc status (diagnostic research) 12
  • Outside research: use as an 'immune booster' and anti-ageing agent, without clinical substantiation
  • Animal models: inflammation suppression, allergy and neuropathic pain

Dosing

Dose
No established dose. Values of approximately 0.5-2 mg per day circulate in user protocols, usually in courses of 10-20 days.
Frequency
Once daily in those protocols
Route
subcutaneous
Duration
Courses of 10-20 days, sometimes repeated a few times a year
  • These doses come solely from user protocols and supplier documentation, not from published clinical studies. There is no dose-response research in humans.
  • The old studies in immunodeficient children gave FTS intravenously, not subcutaneously, on schedules tied to individual patients rather than to a validated dose 4; they are not comparable with the protocols mentioned above.
  • Because activity depends entirely on bound zinc in an equimolar ratio, and measured thymulin activity falls in zinc deficiency and is restored by zinc supplementation 12, administration without adequate zinc status is theoretically pointless; this has never been systematically tested in humans.
  • The very short half-life makes the rationale for once-daily administration unclear.

These figures describe what the literature and published protocols report. They are not advice and not a dosing instruction.

Reconstitution

Vial sizes
10 mg, 20 mg
Solvent
bacteriostatic water (0.9% benzyl alcohol)
Storage
Reconstituted at 2-8 °C, in practice around 3-4 weeks. Powder in the freezer at -20 °C, protected from light and moisture.

Worked example

10 mg vial + 2 ml bacteriostatic water = 5 mg/ml. 1 mg corresponds to 0.2 ml, that is 20 units on a U100 insulin syringe.

Do not shake; let the water run down the wall of the vial. Bear in mind that the stability of thymulin in solution is not publicly documented.

Work it out for Thymulin

Safety

Side effects

  • No systematically collected side effect profile in humans — the absence of reported side effects here mainly means that there is hardly any research
  • Injection site reaction (expected with any injectable peptide)
  • Theoretical: exacerbation of autoimmune processes through T cell stimulation
  • Unknown risks with long-term use

Do not use if

  • Autoimmune disease (theoretical risk of exacerbation)
  • Immunosuppression after organ transplantation
  • Pregnancy and breastfeeding: no data
  • Lymphoproliferative disorders: no safety data

Interactions

Not studied. Biological activity depends on an equimolar bound zinc ion 12, which makes zinc status and agents affecting zinc absorption theoretically relevant. Interaction with immunosuppressants is plausible but has not been studied.

Sources