Thymalin

Origin and structure

Thymalin (Russian: Тималин, sometimes spelt timalin) was the first of the so-called peptide bioregulators developed by Vyacheslav Morozov and Vladimir Khavinson in the Soviet Union: polypeptide complexes extracted from the organs of young animals. It was first described in 1981. Thymalin is made from calf thymus by mild acid extraction, and the medicine is the resulting mixture of polypeptides as a whole. It therefore has no single amino-acid sequence, molecular formula or molar mass.

Khavinson's group later isolated the dipeptide Glu-Trp (EW) from the mixture by liquid chromatography; made synthetically, it became a separate medicine, Thymogen. A 2020 analysis by the same circle, using mass spectrometry and chromatography, reported two further short peptides in thymalin: the dipeptide Lys-Glu (KE) and the tripeptide Glu-Asp-Pro (EDP). The group regards these short peptides as the active part of thymalin; that view comes from its own work.

The registered product is a white or yellowish freeze-dried powder in 10 mg vials for intramuscular injection; in the Belarusian version the only other ingredient is 20 mg of glycine per vial. In Belarus it is made by Belmedpreparaty in Minsk; in Russia it carries registration number LS-000267, dated February 2010.

How it is thought to work

The thymus is the organ in which T cells, the white blood cells that steer cellular immunity, mature, and it shrinks with age. According to its Belarusian product information, injected thymalin helps lymphoid cells mature, shifts the number and ratio of helper and suppressor T cells, regulates antibody-based immunity and stimulates phagocytosis, the uptake of microbes by scavenger cells. The same text says that its use rests on many years of practical experience rather than on controlled trials.

How thymalin is absorbed, distributed and cleared after an injection has never been studied, the label adds, and when swallowed it is rapidly inactivated in the gut. Khavinson's group proposes that the short peptides in the mixture enter cell nuclei, bind to particular DNA sequences or histone proteins and so change which genes are active. That idea rests on the group's own molecular modelling and cell-culture experiments; it has not been tested in people.

Is thymalin approved?

Not in the EU or the US. No medicine containing thymalin has been authorised by the EMA or the FDA, and none is registered in the Netherlands, so it may not be sold or promoted here for human use.

It is an authorised medicine in Russia and Belarus. In Belarus it was first registered in 1995; the current registration dates from November 2019, has no end date, was brought in line with the rules of the Eurasian Economic Union in December 2025, and makes thymalin prescription-only. The label lists add-on treatment of conditions with suppressed cellular immunity: in adults, acute and chronic purulent and inflammatory infections, suppressed immunity after radiotherapy or chemotherapy for cancer, and prevention of infections after those treatments; in children, the infections only. The same label says that, for now, bovine thymus preparations should be used only where there is clear immunodeficiency.

In the US, thymalin does not appear on the FDA's list of substances nominated for pharmacy compounding (May 2026 edition). The similar-sounding thymulin acetate does, among the substances nominated without adequate support, but it is a different molecule.

Vials sold online as 'Thymalin' for research are not the Russian or Belarusian medicine. Because thymalin is defined by how it is extracted rather than by a sequence, the name on a vial does not by itself establish what the vial contains.

What the research shows

Europe PMC lists about 250 papers with thymalin in the title or abstract. More than 200 are in Russian, three-quarters appeared before 2000, and every clinical study among them was carried out in Russia or another former Soviet state. Typical reports describe a few dozen patients and measure immune or clotting markers in blood rather than infections, hospital stays or deaths. The Belarusian product information, approved in 2019, states plainly that thymalin has not been studied in controlled clinical trials; one small randomised trial has been published since. The studies cited most often:

• Older people (Khavinson and Morozov, Neuro Endocrinol Lett 2003): institutes in St Petersburg and Kyiv followed 266 older people for six to eight years; thymalin, the pineal extract epithalamin or both were given in the first two to three years. Mortality was reported as 2.0 to 2.1 times lower with thymalin than in the control group, and 4.1 times lower in a group given both extracts every year for six years. The abstract gives no group sizes and does not describe how people were assigned or whether anyone was blinded, and the study was run by thymalin's developers.
• Severe COVID-19 (Kuznik et al., Adv Gerontol 2021): a single-hospital trial in Chita, Russia, randomised 80 patients (mean age 62) to standard care plus 10 days of thymalin (36 patients) or standard care plus saline injections (44), in a design described as single-blind. Clinical improvement was more frequent with thymalin (80.5% versus 59%), and 19.4% died in hospital against 40.9% (p = 0.039 for both), but time to improvement and the follow-up lung scans did not differ. The thymalin group started with lower lymphocyte counts and higher CRP, adverse events were not reported, no trial registration is given, and Khavinson was a co-author.
• Severe COVID-19, retrospective (Kuznik et al., Russ J Immunol 2022): the same Chita group looked back at the records of 87 patients and reported that immune-cell counts had largely normalised by day six with thymalin added to standard care, but not with standard care alone. A look back at existing records cannot show cause and effect.
• Earlier clinical reports: from the 1980s onwards, small studies added thymalin to standard treatment in conditions as varied as peritonitis, burns, tuberculosis, influenza, psoriasis and schizophrenia, and generally reported that immune markers moved back towards normal; some also reported shorter hospital stays. The abstracts rarely describe randomisation or blinding, and none of these studies has been repeated outside the former Soviet Union.

Thymalin, thymulin and other thymus products

The names are easily confused. Thymulin is a different substance: a single small peptide made by the thymus, the zinc-bound and active form of what was first called serum thymic factor, named in the early 1980s by Mireille Dardenne, Jean-François Bach and colleagues. Thymulin acetate, not thymalin, is the name on the FDA's compounding nomination list. Thymosin alpha-1 (thymalfasin) and TB-500, a derivative of thymosin beta-4, are single defined peptides with their own articles on this wiki, and Thymogen is the synthetic dipeptide Glu-Trp first isolated from thymalin. Thymalin is the whole extract.

Thymus products made outside the Soviet Union were tested in randomised trials. A Cochrane review of 26 trials in 2,736 people with cancer, 20 of them testing the extracts thymostimulin and thymosin fraction 5 and six testing synthetic thymic peptides, found that adding an extract to chemotherapy or radiotherapy did not improve survival or tumour response, although it did reduce severe infections. Thymalin was not among the products studied, so the review shows what this class of extract achieved under trial conditions, not what thymalin does.

The Belarusian label advises against combining thymalin with other thymus products that work in a similar way, and names T-activin, thymactide, Thymogen and thymoptin.

Side effects and warnings

The Belarusian product information lists only allergic reactions to the components and itching or redness at the injection site, and gives no frequency for either. No study has collected side effects systematically: the 2021 COVID-19 trial did not report adverse events, so how often problems occur is unknown.

The label rules thymalin out in pregnancy, during breastfeeding and in children under one year, advises against it at 12 to 17 years because the thymus is most active around puberty, and asks for caution in people prone to allergies and for treatment to be monitored with immune tests. It names the days around menstruation, some endocrine conditions such as pituitary adenoma and acromegaly, and childhood up to puberty as relative contraindications, and warns that side effects may be more frequent with severe endocrine disorders and in the second half of the menstrual cycle. According to the label, thymalin may act in synergy with growth hormone, luteinising hormone and oestrogens, and on the lymphatic system and bone marrow it counters the effects of progestins, androgens and adrenal hormones. The label specifies deep intramuscular injection and warns against intravenous use, and in animal experiments long-term high doses made the thymus shrink.

Frequently asked questions

Is thymalin the same as thymulin?

No. Thymulin is a single small peptide made by the thymus that is only active with zinc bound to it; thymalin is a whole extract of calf thymus containing many peptides. Thymosin alpha-1 and Thymogen are different substances again. In the US, the name on the FDA's compounding nomination list is thymulin acetate, not thymalin.

Is thymalin legal in the Netherlands?

Thymalin is not a registered medicine in the Netherlands or anywhere else in the EU, so it may not be sold, advertised or supplied for human use. Its status as a medicine in Russia and Belarus does not change that. Buying and selling it as research material is a different status, which our guide on research-use-only products in the Netherlands explains.

Is thymalin banned in sport?

It is not named on the 2026 WADA Prohibited List, and WADA has not ruled on it publicly. Class S0 covers substances that no government health authority has approved for human use; thymalin is approved in Russia and Belarus, so it does not plainly fall there, but that is a reading of the rules, not a ruling. The Dopingautoriteit applies the same list in the Netherlands.

Does thymalin slow ageing?

That claim rests mainly on one study by its developers, in which 266 older people were followed for six to eight years and mortality was reported as 2.0 to 2.1 times lower with thymalin than in controls. The abstract gives no group sizes and no details of allocation or blinding, and no group outside the former Soviet Union has repeated it. Ageing is not an indication on the Belarusian label.

Did thymalin work against COVID-19?

One small trial points that way, but it is far from proof. In a single hospital in Chita, 80 patients with severe COVID-19 were randomised to thymalin or saline injections on top of standard care; 19.4% died on thymalin against 40.9% on saline. Time to recovery and lung scans did not differ, the groups were unequal at the start, no trial registration is given and no larger trial has been published.

Is research-grade thymalin the same as the Russian medicine?

No. The registered medicine is made under a marketing authorisation that fixes how it is produced and tested. A vial sold as 'Thymalin' for laboratory use has no marketing authorisation, and because thymalin has no defined sequence, the name alone says little about what the vial contains; that rests on the supplier's own analysis. It may not be used in people.

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.