Thymulin (serum thymic factor)

What thymulin is, and what it is not

Thymulin is a small hormone made only by the epithelial cells of the thymus, the organ in which T cells mature. In 1973 Jean-François Bach and Mireille Dardenne in Paris described a factor in mouse serum that disappeared within hours of removing the thymus and returned after a thymus graft. Their group purified this serum thymic factor, facteur thymique sérique (FTS) in French, from 1,000 litres of pig serum and by 1977 had published its sequence: nine amino acids, pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn. Its formula is C33H54N12O15 and its molar mass about 859 g/mol.

In 1982 the Paris group reported that the peptide is biologically active only when zinc is bound to it, one zinc ion per peptide working best; without zinc it is inactive. They proposed the name thymulin for the zinc-bound form, also written FTS-Zn or zinc-thymulin. The synthetic peptide tested in patients in the 1980s carried the international non-proprietary name nonathymulin; the substance nominated for US pharmacy compounding is thymulin acetate.

Despite the similar names, thymulin is neither thymalin nor thymosin alpha-1, two thymus products with their own articles on this wiki. Thymalin is a polypeptide extract of calf thymus, developed in the Soviet Union and registered as a medicine in Russia and Belarus; it is a mixture rather than one peptide. Thymosin alpha-1 (thymalfasin, sold as Zadaxin) is a different single peptide of 28 amino acids, approved in Italy, China and other countries. Thymulin shares neither the sequence nor the approvals of either.

How it is thought to work

In laboratory studies thymulin pushes immature cells towards becoming T cells: it makes precursor cells from mouse bone marrow and spleen take on T-cell features, it did the same in blood cells from four of five immune-deficient children, and some human T-cell lines carry high-affinity binding sites for it. In mice it acts on several stages of T-cell development, inside and outside the thymus. Once injected it is cleared quickly; the authors of the 1987 arthritis trials give a half-life of 30 to 60 minutes.

Thymulin is also part of a two-way link between the thymus and the hormone system. Hormones such as prolactin, growth hormone and thyroid hormone influence how much of it the thymus makes, and blood levels rise at night, an effect that rat studies trace to melatonin. In return, rodent studies suggest that thymulin acts on the pituitary: neutralising it with antibodies from birth in normal mice altered the hormone-producing cells of the pituitary and, by puberty, lowered the reproductive hormones LH and FSH; and in athymic 'nude' mice, which lack it, a thymulin gene given at birth largely prevented the ovarian damage these mice develop by ten weeks of age.

Active thymulin in the blood falls with age and with zinc shortage. In people, levels were found to be stable until about age 20 and lower after that; Italian researchers later showed that in people over 50 much of the peptide in the blood is inactive, because adding zinc to their plasma in the test tube brought activity back to the level seen in young people. In volunteers put on a zinc-poor diet, thymulin activity dropped and recovered with zinc, which is why it has been used as a sensitive marker of mild zinc deficiency.

In animals thymulin also has anti-inflammatory effects. In rats with inflammation caused by bacterial endotoxin, relatively high doses of thymulin or of a synthetic analogue called PAT reduced pain and inflammatory cytokines, whereas very low doses made the animals more sensitive to pain. None of these effects has been shown to bring a clinical benefit in people.

Is thymulin approved?

No. No medicine containing thymulin is authorised by the EMA or the FDA, the EMA has never given it an orphan designation, and the CBG's Geneesmiddeleninformatiebank, the Dutch medicines register, lists no product with it. We found no country where it is an approved medicine: as nonathymulin it was tested in small trials in the 1980s, and we found no record of later development.

In the US, thymulin acetate appears on the FDA's list of bulk substances nominated for pharmacy compounding, in category 3: substances nominated without adequate support (May 2026 edition). It is not in category 1, the substances the FDA is evaluating for use in compounding.

In sport, thymulin is not named on the WADA Prohibited List for 2026 or 2027. Class S0 bans, at all times, any substance not covered elsewhere on the list that has no current approval from a government health authority for human use. Because thymulin is not approved anywhere we know of, it would fall under S0; that is our reading of the rules, not a WADA decision. The Dopingautoriteit applies the same list in the Netherlands.

Thymulin sold online as a research peptide, and the 'zinc thymulin' sprays and serums marketed for hair loss, are not authorised medicines. No medicines regulator has approved thymulin for hair loss or for any other use.

What the research shows

PubMed lists about 550 papers with thymulin or one of its older names in the title or abstract; nearly three-quarters appeared before 2000, and about half report animal work only. Many human papers only measure thymulin in blood, as a marker of thymus function or zinc status. Thymulin itself has been given to people in a handful of small published studies, and ClinicalTrials.gov lists no trial in which it is given. The main results:

• Immune deficiency in children (Lancet 1982): three children with IgA and IgE deficiency and T-cell defects, two of them related and with ataxia telangiectasia, were given synthetic FTS intravenously. The authors reported fewer and milder infections, better cellular-immunity tests and, within four weeks, IgA appearing in the two children who had none. There was no control group.
• Rheumatoid arthritis (Ann Rheum Dis 1987): two double-blind, placebo-controlled six-month trials at Cochin Hospital in Paris, with the drug supplied by the French company Choay. In the first, 49 patients received 1 mg or 5 mg nonathymulin or a zinc-containing placebo; at least moderate improvement in the overall assessment was seen in 62.5% on 5 mg against 17.6% on placebo (the paper's summary gives 56% against 17%), and grip strength, a function score and a joint-tenderness score improved more, while steroid use fell. The groups were unequal at the start, though: 10 of 16 patients on 5 mg had normal suppressor T-cell function, against 3 of 16 on 1 mg and 4 in the placebo group, and normal function went with a better response. In the second trial, 30 patients received 10 mg daily or placebo; 53.3% improved at least moderately on nonathymulin, not significantly more than on placebo.
• Multiple sclerosis (Acta Neurol Scand 1989): 40 patients with active multiple sclerosis and moderate disability received nonathymulin or placebo under the skin for six months, double-blind, and were followed for six months more. Disability scores did not differ, and the authors concluded that it was not effective.
• Zinc studies: in two volunteers on a zinc-poor diet and in 12 adults with mild zinc deficiency, blood thymulin activity was low and returned to normal with zinc (J Clin Invest 1988); a placebo-controlled zinc trial in 27 people with Crohn's disease found the same at the higher of two zinc doses. These studies gave zinc, not thymulin, and measured thymulin as a marker.
• Animal studies: in old mice with a lupus-like disease, thymulin treatment sharply lowered anti-DNA antibodies and kidney deposits; in rats with collagen-induced arthritis it reduced paw swelling; and in mice with chronic chemically induced colitis it reduced weight loss and deaths, although it did not change acute colitis. In mice with established allergic asthma, a single dose of a thymulin gene delivered into the airways by nanoparticles normalised inflammation, fibrosis and lung mechanics within 20 days (Sci Adv 2020). None of these uses has been tested in people.

Thymulin and hair growth

Thymulin is now marketed online, often as 'zinc thymulin', in sprays and serums for hair loss. The evidence behind those claims consists of one set of laboratory experiments and one small human study, and no randomised trial of thymulin for hair loss has been published or registered:

• Scalp follicles in culture: hair researchers working with the German diagnostics company Immundiagnostik kept hair follicles from the scalps of three women who had face-lift surgery alive in culture for nine days. Thymulin did not make the hair shafts grow longer; in one of the experiments, growth at 100 picograms per millilitre was lower than in untreated follicles. Treated follicles did stay longer in the growth phase (anagen) and held more melanin. The company described the work in a patent application first filed in 2007, and the group later published a short research letter on thymic peptides and hair growth (J Invest Dermatol 2012).
• Topical pilot (Hair Ther Transplant 2017): an Australian maxillofacial surgeon gave 18 adults with pattern hair loss (17 men, aged 35 to 90) a spray containing 0.0005% zinc-thymulin for 4 to 10 months, without a control group. Blinded assessors scoring photographs found no significant change in the whole group (P = 0.07), but did find one in the 11 who used it for at least six months (P = 0.045); in the 10 people whose photos could be magnified, the share of intermediate hairs rose. The author declared a financial interest and had filed a patent application on zinc-thymulin, and the article is not indexed in PubMed.

Side effects and warnings

Almost all safety data come from the 1987 arthritis trials, in which 47 patients were assigned to thymulin injections for up to six months. Pain at the injection site was the most common complaint: nine patients in the first trial had it, and in the second, with daily injections, all patients did, on placebo as well; the authors blamed the zinc salt that both preparations contained.

One patient on 10 mg had low blood pressure and swelling of the larynx a few minutes after the first injection, which settled within 30 minutes after an intravenous corticosteroid. In the 5 mg group one patient developed a very low platelet count and another vasculitis; the authors considered both more likely to be complications of the arthritis, because they recurred long after treatment had stopped.

The multiple sclerosis trial recorded no significant side effects. In the topical hair pilot one person had an hour of redness on the forehead, which the author put down to the citric-acid buffer, and no one reported scalp irritation. Long-term use, use in pregnancy and the products sold online have never been studied; for research peptides, identity, purity and zinc content are only what the supplier's own analysis states.

Frequently asked questions

Is thymulin the same as thymalin or thymosin alpha-1?

No. Thymulin is a single peptide of nine amino acids that the thymus makes itself and that only works with zinc bound to it. Thymalin is a whole extract of calf thymus containing many peptides, registered as a medicine in Russia and Belarus. Thymosin alpha-1 is another single peptide, of 28 amino acids, approved as Zadaxin in Italy, China and other countries. They differ in structure, evidence and legal status.

Does thymulin help against hair loss?

That has not been shown. In scalp hair follicles kept alive in the laboratory, thymulin kept follicles in the growth phase longer and raised their melanin, but it did not make the hair grow longer. The only human study is an uncontrolled pilot in 18 people with pattern hair loss, run by an author with a financial interest; its main photo score improved only in those who used the spray for six months or more. No randomised trial has been published or registered.

Is thymulin legal in the Netherlands?

Thymulin is not a registered medicine in the Netherlands or elsewhere in the EU, so it may not be sold, advertised or supplied as a medicine for use in people. In a cosmetic it falls under the EU Cosmetics Regulation, which requires a safety assessment of the finished product. Buying and selling it as research material is a different status, which our guide on research-use-only products in the Netherlands explains.

Is thymulin banned in sport?

It is not named on the WADA Prohibited List for 2026 or 2027. Class S0 bans, at all times, substances that no government health authority has approved for human use, and we found no country where thymulin is approved, so S0 would appear to apply. That is a reading of the rules, not a ruling. The Dopingautoriteit applies the same list in the Netherlands.

Why does thymulin need zinc?

The peptide binds one zinc ion, and only that zinc-bound form is biologically active; without zinc it does nothing in laboratory tests. As a result, active thymulin in the blood falls when people are short of zinc and rises again when zinc is restored, which has made it a sensitive marker of mild zinc deficiency. Those studies gave zinc, not thymulin.

Does thymulin boost the immune system or slow ageing?

That has not been shown in people. Blood levels of active thymulin fall with age, partly because less of it carries zinc, but no trial has tested whether giving thymulin improves immunity or slows ageing in healthy or older people. The human trials treated rheumatoid arthritis, multiple sclerosis and three children with immune deficiency.

Storage and handling

Store according to product-label instructions and batch handling notes. Lyophilized research peptides are commonly kept dry, protected from light, and handled with clean laboratory technique.

References

Checked against these sources on 28 October 2026.

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