What it is
Thymalin is not a single molecule. It is a purified extract from the thymus glands of calves, containing many small protein fragments (peptides). The thymus is an organ in the chest where a type of white blood cell, the T cell, matures. The idea behind thymalin was that peptides from a young animal’s thymus might influence immune function in people whose own thymus has shrunk with age or illness.
In Russia it is a registered medicine, given as an injection into muscle, and described there as an immune modulator. It is not approved in the United States, and because it is a mixture, 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 created in the Soviet Union in the 1970s by two researchers, Vladimir Morozov and Vladimir Khavinson, at the S.M. Kirov Military Medical Academy in Leningrad (now St Petersburg). It was one of the first of a family of animal-organ peptide extracts they developed, alongside epithalamin from the pineal gland, the parent of the synthetic peptide epithalon. According to the developers, health authorities approved thymalin for medical use in 1982, and it remains registered in Russia. Khavinson later headed the St Petersburg Institute of Bioregulation and Gerontology, which continues to publish 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 data on thymalin come from Khavinson’s group and its collaborators in Russia. The best-known report followed 266 elderly people for six to eight years and described fewer deaths among those given thymalin, epithalamin or both; its abstract does not describe blinding or how participants were assigned to groups.
During the COVID-19 pandemic, two small Russian hospital studies added thymalin injections to standard care. One, with 92 patients, reported faster improvement in blood markers of inflammation and clotting. Another reported fewer hospital deaths, but its English and Russian summaries give different figures. No thymalin trial is registered on ClinicalTrials.gov, and 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 apply in the United States. Compounding: thymalin does not appear on any of the FDA’s lists for pharmacy compounding. It does not appear on the FDA’s list of substances nominated for pharmacy compounding, and it is not in the FDA’s “Category 2” of risky substances either. Enforcement: in February 2024 the FDA sent a warning letter to an online seller of “Thymalin”, calling it an unapproved new drug despite its “research” labelling and raising particular concern that it was being marketed for 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.
