Immune and thymic

Thymalin

The registered active substance is the words thymus extract

8 sections

Top of article
What it actually is
What it is supposed to do
What people take it for
The dose question
How to check you have the right molecule
What people get wrong
What is known about harm
The arithmetic

What circulates: 10 mg a day for 5 to 10 days, injected under the skin
What was studied: 10 mg a day for 5 to 10 days, injected into a muscle
The gap: Convention lands on a studied dose
How long it lasts: I could not find one, in any species. My searches returned no pharmacokinetic study of thymalin by any route, which is the kind of study that measures where a dose goes and how fast it disappears, and for an extract with no defined molecule there is no single analyte to measure anyway.

What it actually is

Open the Russian marketing authorisation and read the composition line. The active substance is thymus extract, 10 mg, and the only other ingredient is 20 mg of glycine, with a footnote saying the extract comes from the thymus glands of calves and young cattle up to one year old. That is the registered identity of a licensed medicine. Cerebrolysin at least prints a mass for its fraction. This label prints a quantity of a noun. It is a real prescription medicine in Russia, marketing authorisation dated 21 June 2024, held by Samson-Med of St Petersburg, supplied as a freeze dried powder for a solution injected into a muscle.

What it is supposed to do

The research group behind it describes it in English as a complex of peptides isolated from calf thymus with none heavier than 10 kilodaltons, the unit molecules are weighed in, and as a polypeptide extract of thymus. What is new, and what makes this compound different from the other extracts in this reference, is the direction the evidence is travelling. Nothing has taken Thymalin's record. Thymalin's record is being handed forward: the same group now says the mechanism is due to the short peptides KE, EW and EDP in its composition, and that KE and EW dipeptides are active substances of Thymalin. Both of those are sold as separate products, Vilon and Thymogen, and both can be weighed and confirmed on a certificate, which the extract cannot. That is the trade on offer: an argument built out of calf glands, attached to a molecule a buyer can verify.

What people take it for

Thymic rejuvenation and longevity in healthy adults. The indications section, as both Russian drug references transcribe it, covers immunodeficiency states with depressed cellular immunity: septic processes with bone destruction, infection, suppressed immunity after chemotherapy. Only one of those has a document behind it. Every published human use I could open was in patients rather than healthy adults, and I found no measurement of thymic output in a person given thymalin, either by the blood test that counts newly made T cells or by imaging.

The dose question

What circulates: 10 mg a day for 5 to 10 days, injected under the skin
What was studied: 10 mg a day for 5 to 10 days, injected into a muscle; The Russian label, and every published human use I could open across 25 years

Lands on a studied dose

Nothing drifted on quantity and everything drifted on route. Ten milligrams sits inside the label's own 5 to 20 mg range, is one whole vial, and is the dose in all five published human uses I could open, with the course arithmetic landing inside the label's 30 to 100 mg range too. The label lists injection into a muscle and no other route, every human dose I found in a paper went that way, and I found no published human study giving thymalin under the skin. One vendor protocol page prints 30 units and calls it about 30 micrograms; thirty units is 0.3 mL, and a 10 mg vial made up in the 1 to 2 mL the label specifies holds 3 mg or 1.5 mg in that volume.

Reported because it is what people use. Nothing here recommends any amount.

How long it lasts

I could not find one, in any species. My searches returned no pharmacokinetic study of thymalin by any route, which is the kind of study that measures where a dose goes and how fast it disappears, and for an extract with no defined molecule there is no single analyte to measure anyway.

Route studied

Into a muscle, in every human study I could open: 10 mg daily for 10 days in the geroprotection cohort and in the Chita COVID-19 trial, and 10 mg daily for 5 days in the St Petersburg COVID-19 study. I searched PubMed for thymalin and subcutaneous and got 8 records; one 1998 paper gives thymalin under the skin to CBA mice and broiler chickens and reports it stimulated the immune response only at the injection site.

Route used

Under the skin, at home. The label lists injection into a muscle and no other route, and I found no published human study giving thymalin under the skin.

How to check you have the right molecule

Read the composition line the seller printed, because three different products sell under this name. One vendor page says thymalin has no single defined molecular formula or weight because of its composite nature, then lower down says purity is confirmed by chromatography, and a percentage needs a reference standard to be a percentage of. Another claims at least 99 percent purity and calls its thymalin synthesized, and a synthesised calf thymus extract cannot exist. A third sells thymulin under the name outright, printing a nine residue sequence and a molecular weight of 858.86. The databases carry the same collision: ask PubChem for substances called thymalin and four deposits come back with no structure, ask it for a compound and it hands over thymulin, fully drawn, with the word Thymalin in that record's own synonym list. So the check is one question. Does the label say thymus extract, or does it give you a sequence and a molecular weight? Those are two different products, and one of them is thymulin.

Walked through on two real certificates in how to read a certificate of analysis.

What people get wrong

Two numbers get repeated and both need reading carefully. The first is 266, which is not a trial. Khavinson and Morozov 2003 pooled three cohorts at two institutions: 94 women at a St Petersburg war veterans home randomised four ways, a separate 20 given two agents every year for six years, and 152 people in Kiev randomised three ways on a different schedule. Twenty four people received Thymalin on its own, and in that arm 10 of 24 died over six years against 18 of 22 on placebo. The second is that Thymalin halved hospital mortality, which comes from one trial in Chita and from a secondary endpoint in it. That trial met one of its three primary endpoints and missed the other two, and the treated group took slightly longer to improve.

What is known about harm

The label's entire adverse effects entry, on both Russian drug references I could open, is two words: allergic reactions. Contraindications are hypersensitivity, pregnancy and breastfeeding. That is the whole safety text, and my searches did not fill it in: thymalin with toxicity, safety, adverse or side effect returns 21 records, and reading the titles I found no repeat dose toxicology, carcinogenicity, genotoxicity or pharmacokinetic study among them. It is also a tissue extract from cattle, and I found no statement in either label transcription about source herd status or about transmissible spongiform encephalopathy, the family that includes BSE. That is a gap in what I could read rather than a finding. The animal work that might supply a milligram per kilogram figure does not print one: a 2018 rat sarcoma study calls its doses lower than the therapeutic ones and never states them, and a 2024 rat study of a jaw defect prints no dose anywhere.

The arithmetic

Thymalin is sold in 10 mg vials. Mixing errors put people an order of magnitude off using a perfectly good vial, and the arithmetic is simple enough to check yourself.

Vial	Water	Concentration	In 10 units
10 mg	1 mL	10 mg/mL	1 mg
10 mg	2 mL	5 mg/mL	500 mcg
10 mg	3 mL	3.33 mg/mL	333 mcg

10 units is 0.1 mL on a U-100 insulin syringe, whatever is in it. For any other combination, or to see the arithmetic worked out, use the calculator.

To run your own numbers, use the reconstitution calculator.

Others in Immune and thymic

Everything on this page is a summary. The citations, the studies and the reasoning live in the full entry.

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