Thymulin

FTS (facteur thymique sérique), serum thymic factor, thymulin-zinc, FTS-Zn, Zn-FTS

Immune & bioregulators

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Summary

Class: Naturally occurring nonapeptide (9 amino acids: pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn) produced by thymic epithelial cells; biologically active only when bound to a zinc ion
Mechanism: A genuine thymic hormone that helps T cells mature and keeps immune signalling balanced; in rodents it also damps inflammation and pain
Routes studied: Subcutaneous and intraperitoneal injection (human 1980s studies, rodents); intracerebroventricular (rodent); gene therapy (rodent); community: subcutaneous
Dose range reported: Rodent anti-inflammatory studies: nanogram-to-low-microgram amounts per animal (e.g. 1–5 µg/kg range in some papers; as low as 5–50 ng locally). Early human studies: microgram doses by injection, details vary by study. Community: 1–5 mg "courses" are sometimes described, which is orders of magnitude above anything studied. No validated human dose
Half-life: Minutes in plasma; endogenous levels are picomolar
Storage: Lyophilised: freeze or refrigerate, protect from light. Reconstituted: refrigerate, use within days to ~2 weeks; zinc must be present for activity
Regulatory status: Not approved anywhere

Doses are as reported in studies or by the community — never recommendations.

1What it is

Thymulin is one of the few compounds on this site that is a true hormone in the classical sense: it is made by one organ (the thymus), travels in the blood and acts on distant cells. It was isolated in the 1970s by Jean-François Bach and Mireille Dardenne in Paris as "facteur thymique sérique" (Bach 1977), and shown a few years later to be inactive unless bound to zinc (Dardenne 1982, PNAS). Its blood level falls with age as the thymus shrinks, and falls further in zinc deficiency; giving zinc to zinc-deficient elderly people restores measurable thymulin activity (Prasad 1988; Mocchegiani 1995).

Synthetic thymulin exists and was studied clinically in small numbers in the 1980s, mainly in France, in immunodeficiency and autoimmune settings. Development stalled. In the last two decades the main work has been from a Lebanese group studying its anti-inflammatory and analgesic effects in rodents, and from an Argentine group using thymulin gene therapy in mice. Human interest in the peptide community is modest and mostly framed around "thymic rejuvenation".

2How it's thought to work

T-cell maturation. promotes differentiation of thymocytes and expression of T-cell markers; supports both helper and suppressor/regulatory populations.

Cytokine balance. in rodents it lowers pro-inflammatory cytokines (IL-1β, IL-6, TNF-α) and raises IL-10 in models of exposure and inflammatory pain.

Neuro-immune link. acts within the brain in rodents to reduce inflammation and hyperalgesia, and is itself regulated by growth hormone, prolactin and thyroid hormone.

Zinc dependence. the peptide alone is inactive; the zinc complex is the hormone. This is why zinc status and thymulin levels track each other.

Proposed: a thymic nonapeptide that is only active with a zinc ion bound — the zinc in the figure is part of the molecule, not a cofactor added to it. Falls with age and with zinc deficiency.Schematic — not to scale

3What the research shows

Thymulin as a marker of thymic function and zinc status in humans

Multiple clinical studies have measured thymulin activity in elderly people, in zinc deficiency, in Down syndrome and in HIV, and shown that zinc supplementation restores activity in zinc-deficient groups (Prasad 1988, Am J Med; Mocchegiani 1995, Int J Immunopharmacol; Mocchegiani 1998, Mech Ageing Dev). These are measurement studies, not treatment with thymulin. [4][5]

Graded B (small, dated)

Synthetic thymulin given to humans

Small open and a few blinded studies in the 1980s administered synthetic FTS-Zn to patients with immunodeficiencies, recurrent infections or rheumatoid arthritis and reported modest immune or clinical changes (Bach 1983, Clin Immunol Allergy review; Amor 1987, Rev Rhum †). Sample sizes were small and results were not compelling enough to continue development. [3]

Anti-inflammatory and analgesic effects

In rats and mice, thymulin or its stabilised analogue PAT reduced endotoxin-induced hyperalgesia, lowered inflammatory cytokines in the brain and periphery, and protected against lung injury (Safieh-Garabedian 2002 and later, Neuroimmunomodulation / Brain Behav Immun; Haddad 2011). [6]

Thymulin gene therapy and ageing

In thymus-deficient (nude) and old mice, a single injection of a thymulin-expressing vector produced long-term circulating thymulin and partly restored some immune and endocrine parameters (Reggiani 2009, 2012, Neuroimmunomodulation; Goya group). [7]

"Thymic rejuvenation" in healthy adults

No data. Community claims are extrapolated from the hormone's physiology.

4Reported side effects and interactions

Literature-reported

the early human studies described thymulin as well tolerated at microgram doses; no serious adverse effects reported in the limited data. Rodent work shows no toxicity at effective doses.

Community-reported

few reports; occasional injection-site reaction or transient fatigue.

Theoretical. immune modulation in either direction carries caution in autoimmune disease, transplant recipients and active malignancy; because thymulin is zinc-dependent, excess zinc co-administered "to activate it" can itself cause nausea and copper deficiency.

Interactions. zinc (required for activity); glucocorticoids and ageing lower endogenous thymulin; growth hormone and thyroid hormone raise it. No clinical drug interaction data.

Markers researchers commonly monitor

From the human measurement literature and rodent mechanisms:

Marker	Why it's watched
Serum zinc (and copper)	thymulin is zinc-dependent and low zinc is the most common correctable reason for low thymulin activity; copper falls if zinc is over-supplemented.
CBC with differential, lymphocyte subsets (CD4/CD8, naive T cells if available)	the hormone's target is T-cell maturation.
hs-CRP, IL-6	anti-inflammatory claims in rodents.
TSH, free T4, IGF-1	thyroid hormone and GH regulate thymulin production; context for interpreting any change.
Thymulin activity itself	measured by a rosette-inhibition bioassay in research labs only; not clinically available.

Free for everyone. Safety information is never behind a paywall.

5Reconstitution and handling

Sold as a nonapeptide, sometimes already complexed with zinc and sometimes not; the label should say. with and swirl gently. If the product is zinc-free, it is inactive by definition — adding zinc to a vial without pharmaceutical knowledge of stoichiometry is a community improvisation with no data behind it. Community dose descriptions in milligrams exceed studied amounts by roughly a thousand-fold.

Open in calculator, pre-loaded →

6Commonly studied alongside

Thymosin alpha-1 (set 2) and Thymalin/Thymogen (profile 76) as other thymic products; zinc; GH secretagogues in community "thymic regeneration" protocols (no study basis).

Informational cross-links. Not stack recommendations.

7Regulatory status by region

Region	Status (checked —)
United States	Not FDA-approved; not known to be on the Category 2 compounding list †
European Union	Not authorised
United Kingdom	Not licensed
Australia	Not approved
South Africa	Not registered
Sport	Not named by WADA; non-approved substances fall under S0 †

8Open questions

Would restoring thymulin in older adults do anything that zinc repletion does not already achieve?
Is PAT or another stabilised analogue a better candidate than the native peptide?
No modern controlled human trial of thymulin administration exists; the 1980s data are too small to judge.

9References

1Bach JF, Dardenne M, Pleau JM, Rosa J (1977). Biochemical characterisation of a serum thymic factor. Nature. PubMed · DOI
2Dardenne M et al. (1982). Contribution of zinc and other metals to the biological activity of the serum thymic factor. Proc Natl Acad Sci USA. PubMed · DOI
3Bach JF (1983). Thymulin (FTS-Zn). Clin Immunol Allergy. DOI
4Prasad AS et al. (1988). Serum thymulin in human zinc deficiency. J Clin Invest. PubMed · DOI
5Mocchegiani E, Muzzioli M, Giacconi R (1998). Zinc, metallothioneins, immune responses, survival and ageing. Biogerontology / Mech Ageing Dev [verify]. PubMed
6Safieh-Garabedian B et al. (2002). Thymulin reverses inflammatory hyperalgesia and modulates the increased concentration of proinflammatory cytokines induced by i.c.v. endotoxin injection. Neuroscience. PubMed · DOI
7Reggiani PC et al. (2009). Thymulin gene therapy prevents the reduction in circulating gonadotropins induced by thymulin deficiency in mice. Am J Physiol Endocrinol Metab. PubMed
8Dardenne M, Savino W (1994). Control of thymus physiology by peptidic hormones and neuropeptides. Immunol Today. PubMed · DOI

References are being resolved to PubMed/DOI identifiers; links search PubMed for the citation until then.

† Being confirmed by our reviewers against current sources.

10Community

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11Page history

26 Oct 2026Profile published — awaiting medical review

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