Thymalin

Thymalin is a polypeptide complex extracted from calf thymus, developed in the Soviet Union by the group of Vladimir Khavinson and Vyacheslav Morozov. It has been studied in immune-function models and Russian clinical reports and is not approved by the FDA.

Last reviewed 2026-10-25 by the PeptideWiki editorial team. Editorial policy.

Overview

Thymalin is a preparation of polypeptides isolated from the thymus glands of calves. It was developed in Leningrad in the 1970s and 1980s by researchers led by Vladimir Khavinson and Vyacheslav Morozov, who were working on peptide extracts from organs such as the thymus and pineal gland as potential regulators of immune and age-related functions. Thymalin belongs to the same research tradition as epitalamin, the pineal extract from which the synthetic tetrapeptide epitalon was later derived.

Most of the published work on thymalin comes from Russian institutions and appears in Russian-language journals. It includes animal studies on immune parameters and lifespan, and clinical reports in patients with immune deficiencies, infections, and after surgery or radiation, where thymalin was used as an immunomodulator. These clinical studies are largely small, older and difficult to assess by current standards. Independent international research on thymalin is very limited, and its evidence base is regarded as weak outside its country of origin.

Structure

Thymalin is not a single defined peptide. It is a complex mixture of water-soluble polypeptides obtained from calf thymus by extraction and purification, and its exact composition is not fully specified in the international literature. Researchers from the same group reported that short peptides can be identified in the preparation, and the synthetic dipeptide Glu-Trp (thymogen) was described as derived from work on thymalin. Because it is a biological extract, batch-to-batch composition and the absence of animal-derived contaminants are central quality questions, and molecular weight cannot be computed from a single sequence.

Mechanism

The mechanism of thymalin has not been defined at the molecular level. Studies from the originating group describe effects on T-lymphocyte numbers and differentiation, on the balance of lymphocyte subsets, and on other immune and blood-clotting parameters in animals and patients. Later work by the same school proposed that short peptides in such extracts act as regulators of gene expression, a hypothesis that has not been widely tested by independent laboratories. Because thymalin is a mixture, effects cannot be attributed confidently to any particular component.

Research

Immune function

The core of the thymalin literature examines immune parameters in animals and in patients with conditions associated with reduced immune function. Reports describe changes in T-cell counts, lymphocyte proliferation and related measures after treatment. Most of these studies are small, frequently lack modern randomization and blinding, and were published in journals with limited international visibility. They show that the preparation was used clinically in the Soviet Union and Russia, but they do not meet current standards for establishing efficacy.

Aging and lifespan studies

The Khavinson group has reported studies in rodents and in elderly human cohorts suggesting associations between thymalin or combined thymalin and epitalamin treatment and measures of survival and physiological function. These studies are uncommon in design, often long-term and observational in character, and have not been replicated by independent groups. They are frequently cited in discussions of peptide bioregulators, but the evidence should be interpreted with considerable caution.

Clinical use in Russia

Thymalin has been used in Russia as an immunomodulating medicine in settings such as recovery from infection, surgery and radiation exposure. Published accounts of this use come largely from the developing institutions. The clinical literature is extensive in number but heterogeneous, and it is not readily accessible in English. Systematic reviews meeting international standards are lacking, so it is difficult to judge which clinical effects, if any, are robust. Researchers should also note that manufacturing methods may have changed over the decades of use.

Evidence quality

Thymalin illustrates the challenges of evaluating older organ-extract preparations: undefined composition, a literature concentrated in one research school, and few rigorous controlled trials. It is distinct from thymosin alpha 1 (thymalfasin), a single defined peptide originally isolated from a different thymus extract. Researchers should avoid treating findings for one thymus-derived product as applicable to another. Its composition, sourcing and evidence record each need separate evaluation.

Regulatory status

Thymalin is not approved by the FDA for any use and is not on the Section 503A bulk drug substances list. It has been used as a medicine in Russia; its status in other countries should be checked locally. As a bovine-derived extract, it would also raise questions about animal-tissue sourcing in many jurisdictions. For sport, check the current WADA Prohibited List.

Status changes often. See the regulatory tracker for dated updates.

Quality and identity testing

Because thymalin is a polypeptide mixture rather than a single peptide, a standard identity test against one expected mass is not possible. Meaningful characterization would include an HPLC or electrophoretic profile compared with a reference standard, mass spectrometric profiling of major components, total protein or peptide content, and tests for bioburden and endotoxin. Information on the animal source and on screening for transmissible agents is relevant for a bovine tissue extract. Material sold under this name that consists of a single short synthetic peptide is not equivalent to the original extract and should be labeled accordingly.

For a walkthrough of each section of a certificate, see how to read a COA.

Storage and stability

Store lyophilized thymalin sealed at -20 °C or in refrigerated conditions as specified by the supplier's documentation, protected from light and moisture. As a mixture of polypeptides, it may be susceptible to proteolysis and microbial growth once in solution, so solutions should be prepared aseptically in sterile buffer, kept cold, used promptly, and aliquoted for any longer storage at -20 °C or below. Avoid repeated freeze-thaw cycles.

Download the Thymalin data sheet (PDF): sequence, masses, expected MS ions and handling on one printable page.

Latest research

Frequently asked questions

Related compounds

• Thymosin α1

  Thymosin α1 is a 28-amino-acid N-acetylated peptide derived from prothymosin α. Its synthetic form, thymalfasin (Zadaxin), is approved in several countries outside the US and has been studied as an immune modulator in clinical trials.

• Epitalon

  Epitalon is a synthetic tetrapeptide (Ala-Glu-Asp-Gly) developed by Vladimir Khavinson's group in St. Petersburg, based on a pineal gland extract. It is studied in aging and telomere research, with evidence coming mostly from that group.

• Pinealon

  Pinealon is a synthetic tripeptide (Glu-Asp-Arg) from Vladimir Khavinson's group in St. Petersburg, one of their short peptide bioregulators. It has been studied mainly in cell and animal models of neural aging and stress, with evidence mostly from that group.

• Thymosin β4

  Thymosin β4 is a naturally occurring 43-amino-acid peptide that binds monomeric actin and is abundant in many cell types. It has been studied in animal models of tissue repair and in human trials of ophthalmic and topical formulations, and is not approved.

References

1. PubMed: all indexed literature on Thymalin
2. ClinicalTrials.gov: registered studies mentioning Thymalin