Thymalin

What it is. Thymalin is a polypeptide complex extracted from calf thymus - one of the first two products of Vladimir Khavinson's organ-extract programme in Leningrad, alongside the pineal extract Epithalamin that later gave rise to Epitalon [3]. It is a hydrolysate: a mixture of peptides and amino acids defined by how it is made rather than by a structure.

The mortality claim. The 2003 paper in Neuroendocrinology Letters reports that in elderly subjects, mortality fell 2.0-2.1-fold in those treated with Thymalin, 1.6-1.8-fold with Epithalamin, and 2.5-fold with both, compared with control. In a separate group given the combination annually for six years, mortality fell 4.1-fold [1]. A companion review covers the geroprotective claims for both preparations [4].

Take that at face value and it would be the most effective life-extending intervention ever tested in humans. Three things should temper it: the work comes from the institute that developed and sells the preparations; it has never been independently replicated anywhere; and the reporting detail available in English is thin - the abstract gives mortality ratios rather than absolute numbers, group sizes or confidence intervals.

This is not a claim that the result is wrong. It is a statement that the evidence as published cannot distinguish a real effect of this size from the many ways an unreplicated single-centre result can mislead.

The modern work. Rather than characterising the extract as a whole, the group's recent effort has been to identify defined dipeptides within it and study those - KE and EW have been identified in Thymalin and examined for effects on gene expression relevant to COVID-19 pathogenesis [2]. KE is also sold separately as Vilon. This is the same move that produced Epitalon from Epithalamin.

The older clinical literature is Russian-language and mostly from the 1980s: ophthalmic herpes [5], multiple sclerosis [6], and immunofluorescent detection of immunomodulating polypeptides in human thymus [7]. These are reports rather than controlled trials.

Thymalin is presented as restoring thymus-dependent immune function, on the reasoning that the thymus involutes with age and that supplying its peptide products should compensate [3]. That is a coherent hypothesis and it is the same one behind Thymosin Alpha-1, which took the defined-molecule route instead.

The difficulty is that a hydrolysate has no single mechanism to characterise. Its composition depends on the source tissue and the digestion process, and until recently no component had been identified and tested individually. The KE and EW dipeptide work is the attempt to close that gap [2], and it places Thymalin's proposed mechanism inside the same framework as the rest of the Khavinson short peptides: small peptides entering the nucleus and altering gene expression [8][9].

Whether the dipeptides account for the extract's claimed effects, or whether the extract's claimed effects are real, are two separate open questions.

A lyophilised polypeptide complex from calf thymus, reconstituted for intramuscular injection. Because it is defined by process rather than structure, batch composition is a real variable and there is no published specification in the English-language literature.

This distinguishes it sharply from Thymosin Alpha-1, a defined 28-residue synthetic peptide licensed in around thirty countries [10]. The two are sometimes conflated and should not be.

No adverse effects are reported in the available literature, and the preparation has been in clinical use in Russia for decades.

That record comes with the same limits as the efficacy record: it is largely Russian-language, largely uncontrolled, and comes from the institution that produces the compound. There is no post-marketing surveillance data available in English, no toxicology publication, and no pharmacokinetic study.

A specific point about hydrolysates: an animal tissue extract carries risks that a synthetic peptide does not, including batch-to-batch variation and the theoretical transmissible-agent concerns that apply to any bovine tissue product. Nothing in the available literature addresses how the preparation is screened for these.

No interaction studies exist. The combination that has been studied is with Epithalamin, the pineal extract, which in the mortality report produced a larger effect than either alone [1] - though with the same caveats as the rest of that paper.