Thymalin Is a Calf Thymus Extract, Not a Defined Peptide — And That Breaks Every Identity Test

Thymalin's Russian registration names its active substance as "тимуса экстракт" — thymus extract, 10 mg per vial, from calves and cattle under one year old. No sequence, no molecular weight, no CAS number. So what is a certificate reading 99.2% purity measuring?

That question has a practical answer, and it decides everything else on this page. Thymalin is registered in the bioregulator peptides family alongside compounds that are genuine single molecules, and it is not one. Vendor listings and per-milligram pricing sit on the thymalin compound page.

Is thymalin a peptide?

Not a single peptide. Thymalin's Russian registration names the active substance as "thymus extract," 10 mg per vial, obtained from the thymus glands of calves and cattle under one year of age. The manufacturer, Samson-Med, describes it as a polypeptide complex. No amino acid sequence, no molecular weight and no CAS number is declared in the registration or on the manufacturer's own product page.

The manufacturer's own phrase is "полипептидный комплекс" — a polypeptide complex. That is an accurate description and also a complete one: thymalin is a mixture of peptides extracted from bovine thymus tissue, not a single defined molecule.

This is a category difference, not a detail. Every other compound on this platform is a synthetic peptide with one sequence, one formula and one target mass. Thymosin alpha-1, the compound thymalin is most often confused with, is a defined 28-residue peptide of 3,108.3 Da with a CAS number and a PubChem record. Thymalin has none of those things because there is nothing singular to assign them to.

Thymalin, thymulin and thymogen are three unrelated substances

Thymalin, thymulin and thymogen are routinely conflated in vendor listings, and they are chemically unrelated. Thymalin is an undefined bovine thymus polypeptide extract with no PubChem CID and no formula. Thymulin is a defined nonapeptide, the zinc-dependent serum thymic factor, PubChem CID 71300623. Thymogen is the dipeptide Glu-Trp, CID 100094. Thymosin alpha-1, the fourth name in the cluster, is a defined N-acetylated 28-mer, CID 16130571.

The rule that follows is simple. If a vendor page gives you a "thymalin sequence" or a "thymalin molecular weight," one of two things is happening: they have substituted one of the other three compounds, or they have made it up. Neither figure exists in the product's own registration or in its manufacturer's literature.

Where does thymalin actually come from?

From the thymus glands of calves and cattle under one year of age, processed by a route the manufacturer does not disclose. Thymalin's registration specifies no fractionation procedure, no molecular weight range and no purification specification. A synthetic peptide has a synthesis route that can be described; a bovine tissue extract has a herd, an abattoir and a purification process, and none of those appears in anything a buyer can see.

The finished product is a lyophilisate for intramuscular injection, classified under ATC code L03AX with the other immunostimulants. That is the entire public specification.

For a synthetic peptide, provenance questions have answers a buyer can chase: which facility, which synthesis route, which certificate covers which batch. For animal-derived material the same questions run into biology rather than chemistry, and the documentation stops well before it reaches anything checkable. This is the reason the testing section below reorders the usual priorities.

What can a thymalin purity certificate actually tell you?

Considerably less than the same figure tells you for a defined peptide. HPLC purity is the percentage of total peak area attributable to one analyte, and thymalin has no declared analyte; mass spectrometry needs a target mass, and thymalin has none. A vial labelled thymalin could contain a genuine bovine thymus fraction, a different animal-tissue extract, or a synthetic peptide entirely, and routine HPLC and MS would not distinguish them.

For a defined peptide, verification is straightforward in principle. HPLC establishes that a sample is homogeneous — one peak. Mass spectrometry establishes that the peak sits at the expected mass. Together they tell you the vial contains the molecule on the label. Neither test can do that here, and the reason is structural rather than technical.

A "99% purity" figure on a thymalin certificate is either measuring something that should not be a single peak in a genuine extract, or it is a number produced by an assay that was never designed for this material. Either way it does not mean what the same number means on a thymosin alpha-1 certificate. Mass spectrometry has the same problem in reverse: without a reference sequence there is no target mass to confirm, so MS on a thymalin sample produces a spectrum of many masses and nothing to compare it against.

The practical consequence is that routine testing cannot rule out substitution, and there is no authenticated reference standard that would let it — none that we can establish exists in this market.

That is a different and larger problem than the ones affecting defined peptides. With SS-31 or FOXO4-DRI, one specific attribute — chirality — escapes routine testing. With thymalin, the entire concept of identity verification does not apply. See what HPLC testing can and cannot tell you and red flags in peptide certificates of analysis.

Which tests still matter for thymalin?

Endotoxin and sterility, ahead of purity. Thymalin is an injectable derived from animal tissue, where pyrogen contamination is the realistic failure mode, and purity testing cannot perform its usual identity function because there is no declared analyte to measure against. Net peptide content still works — it separates peptide from salts and water. On our platform, only 2 of 12 displayed thymalin tests include an endotoxin result, and sterility is rarely performed.

If you take one practical point from this article, make it that one. For thymalin, endotoxin and sterility testing carry more weight than purity testing, because purity testing cannot do its usual job and pyrogen contamination is the realistic failure mode for material derived from animal tissue. See endotoxin testing and LAL assay interpretation and peptide sterility testing under USP <71>.

Ask a vendor for an LAL result on the specific batch before you ask about purity. If only one document is available, the endotoxin result is the one worth having.

What is thymalin approved for in Russia?

Immunodeficiency states in adults and children from six months to fourteen years — not anti-aging. Registration ЛП-№(005867)-(РГ-RU), dated 21 June 2024 with indefinite validity, is held by Samson-Med under ATC code L03AX. The approved indications are infectious, purulent and septic processes, thymus dysfunction, acute and chronic viral and bacterial infections, impaired regeneration, and immune or haematopoietic suppression after chemotherapy or radiotherapy. Geroprotection and life extension are not among them.

Thymalin is a genuinely registered medicine in Russia, and the registration is worth reading rather than summarising. The prior registration number was ЛС-000267; the current one carries indefinite validity.

Geroprotection is not an approved indication. Neither is life extension, anti-aging, or immune enhancement in healthy adults. The registered use is treatment of documented immunodeficiency in sick people, mostly children. That is a meaningful gap from what thymalin is sold for in the West, and it is a gap the registration itself makes visible.

Did thymalin double survival in elderly patients?

One 2003 paper claims it did, and the paper cannot support the claim. Khavinson and Morozov reported 2.0–2.1-fold lower mortality with thymalin alone in 266 elderly and older persons observed for 6–8 years, with bioregulators given during the first 2–3 years only. The abstract does not state that the study was randomised, placebo-controlled or blinded, and reports no n per arm, no event counts, no confidence intervals and no p-values.

Thymalin's Western reputation rests almost entirely on that one publication: Khavinson VKh and Morozov VG, "Peptides of pineal gland and thymus prolong human life," Neuro Endocrinology Letters, 2003 (PMID 14523363), published in English.

Those numbers are striking, and the reasons to treat them cautiously are structural rather than a matter of opinion.

The design is not what it is usually described as. The abstract describes clinical assessment of an observed cohort against "controls." How participants were allocated, how the controls were selected, and whether anyone was blinded are not stated in the record. Describing this as a randomised controlled trial — as much content does — is unsupported.

The results are fold-changes without denominators. No n per arm, no absolute event counts, no confidence intervals, no p-values. A 4.1-fold mortality reduction with no denominator is not a result you can evaluate.

And the duration is 6–8 years, not the 6–12 years frequently quoted.

Has any independent group replicated thymalin's results?

We found none. A Europe PMC search for thymalin work by Khavinson returns 92 records, and every clinical or geroprotective thymalin paper we retrieved was authored by Khavinson, Morozov, Kuznik, Linkova or Anisimov — the same St Petersburg group. We can state that we found no independent replication; we cannot state that none exists, because our search was not exhaustive. ClinicalTrials.gov returns totalCount = 0 for thymalin: not one registered study.

That second figure is the more remarkable one. Not one study of this compound has ever been registered on ClinicalTrials.gov — not a completed trial, not a terminated trial, not a recruiting trial. For a substance that has been a registered medicine in Russia for decades and is sold internationally as a longevity intervention, a registry count of zero is a complete answer to the question "what trials are running?"

The single-lineage pattern is the wider context, and it applies across this family rather than to thymalin alone — see bioregulators and the Khavinson peptides. Unconfirmed is a different claim from either proven or debunked, and this article makes the first claim only.

Which thymalin claims survive the evidence?

One of the ten claims below is true without qualification: thymalin is a registered medicine in Russia. Two are fabrications — any stated thymalin sequence or molecular weight, because neither exists in the registration. The anti-aging approval claim is false, the mortality study is not a randomised controlled trial, independent replication was not found, registered clinical trials number zero, and identity confirmation by purity testing is not possible.

Two of those verdicts are worth separating from the rest. "Not found" and "Not listed" are statements about our searching, not about the world; "Fabricated" and "Not possible" are statements about the product's own registration, which is a document anyone can read.

Where does thymalin stand with FDA and WADA?

Nowhere on either. Thymalin does not appear on FDA's active Category 2 list, in the "nominated but withdrawn" table, on the 503A bulks list or on the 503B list — it was never nominated, so FDA has never evaluated it. That absence is not clearance: with no USP monograph and no place in an approved drug, thymalin is an unapproved new drug in the United States. WADA's 2026 Prohibited List does not name it.

Never having been evaluated is a different status from having been evaluated and cleared, and it is frequently presented as the second. Thymalin satisfies none of the three statutory routes for 503A compounding, because all three require something — a listing, a monograph, or a place in an approved drug — that does not exist for it.

On WADA: thymalin is not named on the 2026 Prohibited List. Neither is "thymus." Note that thymosin beta-4 is named at S2.3, a different molecule entirely. We verified name-absence only and did not evaluate the S0 catch-all, so this is not a statement that thymalin is permitted.

Notably, Semax and Epitalon — both from the same Russian bioregulator research tradition — were reviewed at FDA's July 2026 advisory committee meeting. Thymalin was not on the agenda. The full sequence of determinations is in our FDA peptide regulation timeline.

What does Peptigrity's platform data show for thymalin?

The Purity Index records thymalin at 97.89% average across 46 tests from Janoshik, Freedom Diagnostics and Chromate, against 219 verified vendors (verified August 2026), with displayed individual results running from 99.20% to 99.94%. Quantity variance runs −10.4% to +16.5%. Price data shows 14 shops in stock, a median of $4.30/mg and a low of $2.50/mg on a 20 mg vial (verified 10 August 2026). None of those purity figures means what it would mean for a defined peptide.

Two things about the purity numbers. First, we flag an inconsistency on our own compound page: the stated average of 97.89% is lower than the stated lowest recorded test of 99.20%. Either the average is computed over a different test set than the one displayed, or one of the figures is wrong. We are correcting it.

Second, and more importantly — for the reasons set out above, none of these numbers carries the meaning it would carry for a defined peptide. A purity percentage on an undefined extract is measuring homogeneity against no declared standard. We publish the figures because they are what the labs reported. We would not want anyone reading them as identity verification. The Purity Index draws on 11,852 independent lab tests across 118 peptides and 530 tracked shops (verified August 2026), and this is one of the few entries in it where we would tell you to weight the number at close to zero.

Only 2 of the 12 displayed tests include endotoxin results — a notable gap on an injectable animal-derived product, where pyrogen risk is not theoretical. Every result behind these figures is browsable in the independent lab tests database.

Thymalin price data shows vial prices from $25.00 to $138.00 across in-stock vendors. Those figures exclude shipping, taxes and customs, coupon codes, bulk tiers, multi-vial kits and account-gated pricing.

How does thymalin compare with thymosin alpha-1, epithalon and semax?

Thymalin is the only one of the four that is not a defined molecule and the only one that cannot be verified by mass spectrometry. Thymosin alpha-1 is 3,108.3 Da and went through TESTS, a 1,106-patient double-blind trial that came back null in sepsis. Epithalon is 390.3 Da, from the same research group, with no placebo-controlled trial. Semax is 813.93 Da, holds a Russian registration, and FDA found its evidence insufficient.

Thymosin alpha-1 is the instructive comparison. Same organ of origin, same therapeutic rationale, same immune-restoration framing — and a defined molecule that could be, and was, put through a 1,106-patient double-blind trial. That trial came back null, which is disappointing but is also knowledge. Thymalin cannot generate that kind of knowledge, because you cannot run a controlled trial of a substance whose composition is not specified.

The comparison is not an argument that thymalin does nothing. It is an argument that nobody can find out, on the current specification.

Frequently Asked Questions

Is thymalin a peptide?

Not a single peptide. Its Russian registration names the active substance as "thymus extract," 10 mg per vial, obtained from the thymus glands of calves and cattle under one year old. The manufacturer describes it as a polypeptide complex. No sequence, molecular weight or CAS number is declared anywhere.

Then what does a thymalin purity certificate mean?

Considerably less than it does for a defined peptide. HPLC purity measures peak area attributable to one analyte, and thymalin has no declared single analyte. Mass spectrometry needs a target mass, and thymalin has none. Without an authenticated reference standard, routine testing cannot distinguish genuine thymus extract from a different extract or a synthetic peptide.

Is thymalin approved anywhere?

Yes, in Russia — registration ЛП-№(005867)-(РГ-RU), held by Samson-Med, for immunodeficiency states in adults and children from six months to fourteen years. Anti-aging and geroprotection are not registered indications.

Did a study show thymalin halves mortality?

Khavinson and Morozov reported roughly two-fold lower mortality over 6–8 years in 266 elderly participants. The paper's abstract does not state that the study was randomised, placebo-controlled or blinded, and reports no sample sizes per arm, no event counts, no confidence intervals and no p-values. We found no independent replication.

Are there clinical trials of thymalin?

ClinicalTrials.gov returns zero registered studies of thymalin. Not one study of this compound has ever been registered there, which means there is no ongoing trial to wait for and no completed trial to look up.

What should I check before buying?

Endotoxin and sterility, ahead of purity. This is an injectable derived from animal tissue, where pyrogen contamination is the realistic failure mode, and where purity testing cannot perform its usual identity function. On our platform, only 2 of 12 displayed thymalin tests include endotoxin results.

The trial that would settle this

No trial can settle anything about thymalin until the composition is published. A randomised, placebo-controlled, blinded study in a defined immunodeficiency population, reporting n per arm, event counts, confidence intervals and p-values, would answer the question the 2003 paper only gestured at — but it needs a characterised product and an authenticated reference standard first, and nobody is working on either. Replication by any group outside St Petersburg would help as much.

The first row blocks all the others, and it is the one nobody is working on.

Where this leaves thymalin

Thymalin sits in a category of its own on this platform, and the reason is not the strength of its evidence — it is that the compound is not a compound. Everything this site does rests on a chain: identify the molecule, verify the vial contains it, then ask what the evidence says the molecule does. For thymalin the chain breaks at the first link, because the registered product is an extract from calf thymus glands.

There is no declared sequence, no target mass, no CAS number and no reference standard, because the manufacturer specifies the product no further than "thymus extract." Downstream of that, the evidence is one 2003 paper from a single research group reporting fold-changes without denominators, zero registered trials anywhere, and a Russian approval covering paediatric immunodeficiency rather than anything it is sold for here.

The 99.2% on the certificate is not a lie. It is an answer to a question nobody can ask of this material.

Browse the bioregulator peptides category, or our complete peptide guide with 118 compounds (verified August 2026). Compare shops through independent lab tests and community-verified shop reviews.

This article is for educational and informational purposes only and does not constitute medical advice. Peptides discussed may be investigational compounds not approved by the FDA (or equivalent regulators in your jurisdiction) for human use. Always consult a qualified healthcare provider before using any peptide or research compound. Peptigrity is an independent review platform and does not sell, endorse, or recommend specific products or vendors.