Thymulin

Thymulin is an endogenous hormone of the thymus, the gland behind the breastbone where T cells get their training. It is only nine amino acids long and is produced exclusively by the epithelial cells of the thymus. It was discovered in the early 1970s by the group around Bach and Dardenne in Paris, first under the name FTS (facteur thymique sérique, serum thymic factor). Only later did it become clear that the peptide on its own does nothing: it is biologically active only when it has bound a zinc ion. Hence the names zinc thymulin or FTS-Zn.

The thymus shrinks with age. Thymulin levels in the blood fall with it. They peak in children aged 5 to 10, fall from adolescence until the mid-thirties and then stay low (Consolini 2000). Zinc deficiency, immune deficiencies and autoimmune disease also go along with low levels. In a research context thymulin is therefore read as a signal that an ageing or out-of-sync immune system is missing.

It ships as a freeze-dried powder in a 20mg vial that you dissolve in bacteriostatic water and inject subcutaneously. Thymulin is not approved as a medicine anywhere. The human data come from small studies of the 1980s, including two placebo-controlled trials in rheumatoid arthritis, current research runs in animals and cells.

This information is for research and educational purposes only. No medical advice.

The classic role of thymulin is T cell maturation: it drives the differentiation of immature precursors and supports several functions of the T cell subsets, inside the thymus and beyond it. What stands out is that it does not simply turn everything up. In cell experiments the direction of the effect depended on concentration and on the starting state: in blood cells of healthy donors a low concentration raised the messenger IL-1 alpha, in cells of patients with active lupus it lowered it (Safieh-Garabedian 1993). NK cell activity rose at very low concentration and fell at higher concentration (Dokhelar 1983). Studies suggest that thymulin pushes toward balance rather than in one fixed direction.

The second pathway is anti-inflammatory. Thymulin restrains the transcription factor NF-kB, the central switch for inflammatory genes. This lowers the production of IL-1, IL-6 and TNF-alpha in immune cells. That is exactly what Kanemaru 2026 showed in ageing myeloid cells from mice and from older human donors. On top come rat data showing that microgram doses of thymulin reduce inflammatory pain and the cytokines behind it (Dardenne 2006).

The zinc dependence is not a footnote. Dardenne showed in 1982 that the synthetic peptide works in the bioassay only with bound zinc. In zinc deficiency the measurable thymulin activity in the blood therefore drops. Zinc restores it, even in the test tube: part of the peptide then circulates without zinc and inactive (Prasad 1988). In the animal studies the peptide was accordingly given as a zinc complex, usually with an equimolar amount of zinc chloride. The data suggest that an adequate zinc status is the ground on which thymulin can work at all.

There is a third strand: thymulin also acts on the hormone axis. Its production is steered by growth hormone, prolactin and thyroid hormones, among others. In turn it stimulates the release of pituitary hormones such as LH, prolactin and ACTH in animal and cell experiments. Reviews by the group around Goya and Dardenne therefore describe thymulin as a link between thymus and pituitary.

The list is the same as for the other vial peptides:

• The thymulin vial with the freeze-dried powder (20mg)
• Bacteriostatic water to dissolve it
• U-100 insulin syringes
• Alcohol swabs for the vial cap and the skin
• A sealable sharps container for used needles

Because the doses are small (0.3 to 0.5mg out of a 20mg vial), a syringe with a fine scale pays off. Then 3 or 5 units can be read cleanly. No further equipment is needed.

The powder is dissolved in bacteriostatic water. The water volume sets the concentration and thus the units you draw for your dose. With 2ml on 20mg you get 10mg per ml, so 0.3mg is 3 units and 0.5mg is 5 units on the U-100 syringe.

The calculator above does this for any water volume. Pick vial size and water, then concentration and units per dose are right there. For these doses 2ml is the best choice, because every step lands on full units (3 and 5). With 1ml the dose becomes tiny and hard to read, with 3ml 0.3 and 0.5mg fall between two marks.

Just add the bac water to the vial, it does not matter whether it hits the powder directly. Then swirl or shake until everything is clearly dissolved, both are fine. A 20mg vial lasts around 13 weeks at 0.5mg three times a week, so well beyond one phase.

The injection is subcutaneous, into the fat layer under the skin, classically the abdomen (leave two finger widths around the navel), the front of the thigh or the back of the upper arm. The early human studies in children and cancer patients ran intravenously, for self-use subcutaneous is the usual and far simpler route.

• Clean the spot with an alcohol swab and let it dry briefly
• Pinch up a small fold of skin
• Insert the needle at a 45 to 90 degree angle
• Inject, slowly or briskly is both fine, wait a moment, then withdraw
• Put the needle straight into the sharps container

Rotate the site from shot to shot. Local reactions are the most common side effect with peptides, a clean stick and rotating sites keep that small.

The foundations are old and solid: Dardenne 1982 showed in PNAS that the synthetic nonapeptide becomes biologically active only with bound zinc. The first human trials followed right away. Bordigoni 1982 in the Lancet treated three children with IgA and IgE deficiency and T cell defects intravenously with synthetic FTS: infections became rarer and milder, serum IgA appeared for the first time in two children within 4 weeks, vaccine antibodies rose. When treatment paused, the improvement regressed. Dokhelar 1983 gave four cancer patients 10 mcg per kg intravenously every three days and saw low NK cell activity rise and normal to high activity fall, a normalisation rather than a boost at any price. In rheumatoid arthritis an open study and two randomised, placebo-controlled double-blind trials followed (Amor 1987): they compared 1, 5 and 10mg per day. With 5mg, 56 percent of patients improved versus 17 percent on placebo, with minor side effects and no clear change in immune markers. It never led to an approval.

The pain and inflammation research in rats (review Dardenne 2006) added the second strand and an important nuance: tiny nanogram doses triggered hypersensitivity via prostaglandin E2, whereas systemic 1 to 25 mcg reduced inflammatory pain and cytokines. Pretreatment with thymulin was protective even in inflammation directly in the brain. An analogue without the nanogram effect (PAT) worked as strongly as common anti-inflammatory drugs or better in these models. It needed much lower doses to do so. Nasseri 2019 confirmed the anti-inflammatory effect in a 21-day rat model and found less microglial activation in the spinal cord.

Novoselova 2018 treated mice with chronic endotoxin inflammation: two doses of 1.5mg per kg lowered fever, cytokines and lymphocyte death, bound to nanoparticles it worked better in several respects, which the authors attribute to the roughly 10-minute half-life of the free peptide. The most recent work is Kanemaru 2026 in Nature Communications: thymulin was identified as one of the factors in the blood of young mice that restrain the inflammatory bias of aged myeloid cells. Daily doses of 1.5mg per kg reduced the share of inflammatory myeloid cells in old mice within one week. Cell experiments traced this to an inhibition of NF-kB. In tumour models over four weeks thymulin slowed growth, improved the T cell response and survival and sensitised tumours to anti-PD-L1, in old animals but barely in young ones. Blood cells from older human donors responded the same way in the lab. In parallel there are gene therapy experiments in which mice produce the peptide themselves, for example in an asthma model.

The read has to stay honest: the mechanisms are well documented, the human data are around 40 years old, cover few patients and come only from sick people (immunodeficiency, cancer, arthritis). What thymulin does in healthy adults has never been studied in a controlled way. The studies with links are in the source block below.

In the small human studies of the 1980s thymulin was described as well tolerated, in the arthritis trials with up to 10mg a day side effects were minor (Amor 1987). Bach and Dardenne explicitly called it non-toxic in 1989. There are, however, no extensive human safety data, let alone any for self-use in healthy people. What is realistic to expect are local reactions at the injection site such as redness or a small lump.

The animal data give two pointers you should know. First: in rats, nanogram doses triggered pain hypersensitivity, only microgram doses were anti-inflammatory (Dardenne 2006). The steps above, converted, sit clearly in the microgram-per-kg range, but the phenomenon shows that the dose response is not linear. Second: thymulin modulates, it does not blindly boost. In patients with normal to high NK activity it fell under treatment (Dokhelar 1983). Anyone with an already active immune system does not automatically get more.

Because thymulin is immune-modulating and, in animal studies, also hormonally active (influence on prolactin, LH, ACTH), restraint makes sense with autoimmune disease, a cancer history, pregnancy and anything that touches the hormone axis. Medical advice is worthwhile when in doubt. Long-term data are missing entirely.

The undissolved powder is robust, normal room temperature (around 20 to 25 degrees) is fine, ideally kept dark and dry. For longer periods it can also go in the fridge.

Once dissolved, the solution goes into the fridge (2 to 8 degrees) and stays stable there for several months with barely any loss of potency. The bacteriostatic water brings a preservative that keeps the dissolved form stable. At 0.5mg three times a week a 20mg vial lasts around 13 weeks. The solution stays usable long enough for that.

Do not freeze and do not leave it in the sun. A slightly cloudy solution is still usable, only a gel-like or lumpy solution is a real defect.