What it is
Thymalin is not one single substance. It is a cleaned-up extract from the thymus glands of calves. It contains many short chains of amino acids (peptides). The thymus is an organ in the chest. A type of white blood cell, the T cell, matures there. In some people the thymus has shrunk with age or illness. The idea was that peptides from a young animal’s thymus might affect the immune system in these people.
In Russia it is a registered medicine. It is given as a shot into a muscle. There it is described as a medicine that adjusts the immune system. It is not approved in the United States. It is a mix of many parts. So its exact makeup cannot be written as one chemical formula.
Thymalin is a complex of polypeptides extracted from calf thymus, with components up to about 10 kDa according to Khavinson et al. (2021). Because it is a biological mixture, it has no single formula, molecular weight, CAS number or PubChem entry; PubChem’s “Thymalin” synonym is attached to nonathymulin (CID 3085284), a different, defined nonapeptide, and the two should not be confused.
The developer group has proposed several mechanisms. In cultured human haematopoietic stem cells, thymalin lowered expression of CD44 and CD117 two- to threefold and raised expression of the mature T-cell marker CD28 6.8-fold, which the authors interpret as promoting T-cell differentiation (Khavinson et al. 2020). Linkova et al. (2023) identify the dipeptides Lys-Glu and Glu-Trp as active components and propose, from molecular docking and cell studies, that they regulate genes involved in inflammation. These are in-vitro and computational findings from the developing institute. No receptor has been identified, and no pharmacokinetic study of the extract in humans or animals was found for this article.
Who made it and when
Thymalin was made in the Soviet Union in the 1970s. Two researchers created it: Vladimir Morozov and Vladimir Khavinson. They worked at the S.M. Kirov Military Medical Academy in Leningrad (now St Petersburg). They made a family of peptide extracts from animal organs. Thymalin was one of the first. Another was epithalamin, from the pineal gland (a small gland in the brain). Epithalamin led to the lab-made peptide epithalon. The developers say health officials approved thymalin for medical use in 1982. It is still registered in Russia. Khavinson later ran the St Petersburg Institute of Bioregulation and Gerontology. That institute still publishes research on it.
Khavinson and colleagues trace the organ-extract (“peptide bioregulator”) programme to work by V.G. Morozov and V.Kh. Khavinson at the S.M. Kirov Military Medical Academy beginning in the 1970s. Thymalin (thymus) and epithalamin (pineal) were the first preparations; others followed for retina, prostate and brain tissue. The programme rested on the hypothesis that low-molecular-weight organ peptides restore function in ageing or damaged tissue of the same organ.
Khavinson et al. (2021) state that thymalin has been approved by the Ministry of Health of the Russian Federation for medical use since 1982 and is now manufactured by Samson-Med LLC, St Petersburg, under registration certificate 82/1108/8. An earlier review from the same group (Khavinson, Kuznik and Ryzhak 2013) dates the thymus-extraction method to 1974 and the registration to USSR Ministry of Health Order No. 1108 of 10 November 1982. These dates come from the developers and were not checked against the Russian State Register for this article. No patent or regulatory filing outside Russia was found.
What the data say
Almost all published human studies of thymalin come from Khavinson’s group and the people they work with in Russia. The best-known report followed 266 older people for six to eight years. It said fewer people died among those given thymalin, epithalamin or both. Its summary does not say how people were put into groups. It also does not say whether people knew which treatment they got.
During the COVID-19 pandemic, two small Russian hospital studies added thymalin shots to usual care. One study had 92 patients. It reported that blood tests for inflammation and clotting got better faster. The other study reported fewer deaths in hospital. But its English and Russian summaries give different numbers. No thymalin trial is listed on ClinicalTrials.gov. No independent controlled trial outside Russia was found.
Ageing cohort: Khavinson and Morozov (2003) reported on 266 elderly people followed for 6–8 years at institutes in St Petersburg and Kiev, with peptide courses in the first 2–3 years. Mortality was reported as 2.0–2.1-fold lower with thymalin, 1.6–1.8-fold with epithalamin and 2.5-fold with both, against controls; an annually treated subgroup showed a 4.1-fold reduction. The abstract gives no randomisation, blinding or confidence intervals.
COVID-19: Khavinson et al. (2021) describe a single-centre, open-label trial in St Petersburg (April–July 2020), randomised by envelope, in 92 hospitalised adults with lymphopenia and bilateral pneumonia: 42 received thymalin 10 mg intramuscularly once daily for 5 days plus standard care and 50 received standard care alone. The authors report faster falls in IL-6, C-reactive protein and D-dimer and recovery of T-cell indices, and state that no deaths occurred in either group. Kuznik et al. (2022, Chita) compared basic therapy, tocilizumab and thymalin in severe COVID-19 and reported hospital mortality of 40.9%, 28.4% and 20.6% in the English abstract but 40.9%, 28.8% and 16.2% in the Russian abstract; group sizes and allocation are not given. The evidence is small, unblinded and developer-linked.
Regulatory picture
Approval: thymalin is not approved by the FDA. Its approval in Russia does not count in the United States.
Compounding (pharmacies mixing their own versions): thymalin is not on any FDA list for this. It is not on the list of substances put forward for pharmacy mixing. It is also not on the FDA’s “Category 2” list of risky substances.
Enforcement: in February 2024 the FDA sent a warning letter to an online seller of “Thymalin”. The FDA said it was an unapproved new drug, even though it was labelled “research” only. The FDA was especially worried that it was being sold for use in children.
Approval: none in the US. No US development programme for thymalin was found.
Compounding: thymalin does not appear in any category of FDA’s 503A nominations list (updated 2026-05-14), on FDA’s page of Category 2 and withdrawn substances (updated 2026-04-22), or on the 503A bulks list (21 CFR 216.23). This article records compounding status as unknown. No FDA review of thymalin was found.
Enforcement: FDA’s warning letter to US Chem Labs (2024-02-07) found its “Thymalin” to be an unapproved new drug and misbranded under sections 505(a) and 502(f)(1), noting that “research” statements on the labelling did not change that conclusion.
Russia: approved for medical use since 1982 and manufactured by Samson-Med LLC under registration certificate 82/1108/8, according to the developer group. National registration outside the US is not FDA approval.
