What is thymulin? What it does, benefits and what the evidence shows

Thymulin is a nine-amino-acid hormone made by the epithelial cells of the thymus, and it is biologically active only when it is bound to zinc. It is studied for what it does to inflammation, pain and immune function, almost entirely in mice and rats. We found no approval for it as a drug in the places we looked, and no controlled human trial of thymulin as a treatment. The human record is mostly measurements of how much thymulin people have in their blood, plus one small 1982 report in three children. If you came here from a hair-loss claim, we searched PubMed and ClinicalTrials.gov for one and found nothing.

What thymulin is and how it works

Thymulin's sequence, pyroglutamyl-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn, was worked out in 1977 from a peptide isolated from pig serum that was then called the serum thymic factor, or FTS, and a synthetic copy showed the same biological activity as the natural one (Pleau et al., Journal of Biological Chemistry, 1977). The zinc piece came later. In 1982 the same French group showed that FTS lost its activity in their assay when metal ions were stripped out, that adding zinc restored it, and that the peptide and zinc bind at a one-to-one ratio. They proposed the name "thymulin" for the zinc-containing, active form, and called the zinc-free form biologically inactive (Dardenne et al., Proceedings of the National Academy of Sciences, 1982).

A 2014 review describes it as a hormone produced only by thymic epithelial cells, whose production and release are shaped by the neuroendocrine system, and which also acts as a signal to the pituitary and as an anti-inflammatory and pain-modulating peptide in the nervous system (Reggiani et al., Current Pharmaceutical Design, 2014). Levels change across life. In 93 healthy people from newborns to old age, plasma thymulin was detectable at birth, peaked in children aged 5 to 10, fell from adolescence to its lowest value around age 36, and then stayed flat until 80, the oldest person tested (Consolini et al., Clinical & Experimental Immunology, 2000). A falling level is an observation, not proof that putting thymulin back would help.

Approval status

We found no approval for thymulin as a drug. A search of DailyMed on September 29, 2026 returned one product, a pellet labeled "Thymulinum 9C" (9C is a potency notation used for homeopathic remedies), and nothing else. ClinicalTrials.gov returned one record that mentions thymulin, a zinc supplementation trial in infants given oral polio vaccine, not a trial of thymulin as a drug. Thymulin does not appear on FDA's page of bulk drug substances that may present significant safety risks for compounding, which was current as of April 22, 2026 (FDA). That absence means FDA has not listed it there, not that FDA has reviewed it and found it safe. We did not search other regulators' databases, but New Zealand's Medsafe said in a June 2025 classification submission that thymulin does not appear to have entered clinical trials and is not currently scheduled in New Zealand or Australia (Medsafe, June 2025).

What people use it for

What the research actually shows

What has been measured in people

Most human work asks how much thymulin activity people have, not what happens when they are given it. A 1993 trial in 27 patients with Crohn's disease in remission, randomized to two zinc sulfate doses or placebo for 3 months, found that plasma zinc and thymulin activity rose only in the higher-dose zinc group (Brignola et al., Alimentary Pharmacology & Therapeutics, 1993). What was given there was zinc, and thymulin was the readout. It fits the biology (no zinc, no active thymulin) but says nothing about injecting the peptide.

The only report we found of people receiving the thymic factor itself is a 1982 Lancet case series of three children with IgA and IgE deficiency and T-cell defects. Given synthetic FTS intravenously, they had fewer and milder infections, and serum IgA appeared or rose. In two of them, interrupting treatment was followed by a regression of the improvements, which reversed when treatment restarted (Bordigoni et al., The Lancet, 1982). Three children, no control group, more than 40 years ago, and the abstract does not say whether the preparation was the zinc-bound form. It is a lead, not evidence that this works. We found no larger human treatment trial.

Inflammation and sepsis models

In mice given gradually increasing doses of bacterial endotoxin to produce chronic inflammation, thymulin reduced fever, cell death and inflammatory signaling, and a nanoparticle-bound form did better on several measures. The authors concluded it suggests thymulin might be worth testing alongside sepsis treatment (Novoselova et al., PLoS ONE, 2018).

Aging and cancer immunotherapy

The newest paper is the most ambitious. A July 2026 Nature Communications study found pro-inflammatory myeloid cells more common in aged mice and in the blood of older people, and traced the calming signal in young animals to thymulin, which suppressed inflammatory cytokine production through NF-kB signaling. In aged mice with breast tumors, thymulin improved tumor control and survival and sensitized the tumors to an anti-PD-L1 drug (Kanemaru et al., Nature Communications, 2026). The human data in that paper is blood-cell measurement, not treatment. It is one new study, in mouse tumor models, and we found no replication.

Pain

Rat studies point in two directions. Thymulin given into the brain ahead of endotoxin reduced the resulting pain hypersensitivity and shifted brain cytokine levels (Safieh-Garabedian et al., Neuroscience, 2003), and a synthetic thymulin-related analog reduced nerve-injury pain in rats, matching or beating morphine and meloxicam in that model (Saadé et al., Neuroscience, 2003). But the group's own review reports that very small local or systemic amounts of thymulin itself caused hyperalgesia, the opposite of pain relief, and describes the analog as lacking that effect (Dardenne, Saadé and Safieh-Garabedian, Annals of the New York Academy of Sciences, 2006). So the pain findings mostly belong to an analog, not to thymulin, and the dose matters in rats.

Lung disease and gene therapy

In rats given a toxin that causes pulmonary hypertension, injected thymulin prevented the heart and lung changes and the inflammatory profile. The zinc-containing vehicle alone produced part of the same effects, which is a reminder that zinc is doing something (Henriques-Coelho et al., Endocrinology, 2008). In mice with established allergic asthma, treatment with nanoparticles carrying a thymulin-expressing gene reversed inflammation and scarring (da Silva et al., Science Advances, 2020). That is gene therapy, where the body makes the peptide, not an injected vial. A separate line of work built a gene for a thymulin analog and showed an injected viral vector restored circulating thymulin in thymus-removed mice and rats for months (Reggiani et al., Gene Therapy, 2006). Again, this is a research tool, not a description of what a vial does.

A narrow research base

A handful of teams account for the animal papers we opened: Reggiani's group on neuroendocrine and gene therapy work, Novoselova's on inflammation models, and Dardenne, Saadé and Safieh-Garabedian on pain. We did not find independent replication of the main findings. We found no controlled human trial of thymulin for hair growth, skin, longevity, or general immune boosting.

Side effects and risks

No dedicated human safety study of thymulin exists that we could find. The 1982 case series does not report side effects in its abstract, and it involved three children. What the record gives us:

• Pain signaling is dose-sensitive in rats. Very small amounts caused hyperalgesia in the research group's own review (Dardenne et al., 2006). Nobody has tested whether that carries over to people.
• Zinc confounds the results. The pulmonary hypertension study saw part of the benefit from the zinc-containing vehicle alone (Henriques-Coelho et al., 2008), so some effects credited to thymulin may partly be zinc.
• No approved product. None turned up in our search, so we found no regulator-reviewed safety profile.
• Unknown long-term effects. Every study above was short, in animals, or in a tiny number of patients.

Two grey-market-specific risks apply on top: purity and amount in the vial, covered next, and the zinc question. The 1982 work found the zinc-free peptide inactive, so ask whether a seller's product is described as the zinc-bound form at all, and what the lab report actually measured.

What the lab tests show

As of September 29, 2026, VendorVerify's database holds one thymulin vial, from May 2025. It measured 99.68% pure and came in about 25% over its labeled amount, which is under our failure line of more than 50% over. One vial cannot tell you about any vendor or batch, and a purity figure describes the peptide, not whether it is in a zinc-bound form. If you have had a thymulin vial tested, submitting the report is the fastest way to make this section useful.

Because we don't have enough lab data on this compound to rank vendors for it, here are the highest-ranked vendors across all compounds right now. A vendor's overall record is a signal, not a guarantee for a compound they have never had tested.

Buying smarter

Check our thymulin results page for anything new, then look at each vendor's full record and how many reports sit behind the score. Treat a vendor-posted COA as a starting point (how to read a peptide COA, fake peptide COAs). With one vial in our data, an independent test of your own vial is the only way to know what you have; how to get a peptide tested walks through it, and endotoxin in research peptides covers when to add that test.

If a report comes back a fail, stop using that batch, tell anyone who bought from the same run, bring the report to the vendor, and submit it to VendorVerify. Do not mix it up with thymosin alpha-1, a different peptide with human data, or with TB-500. Our peptide hub lists every compound we track, and what are grey market peptides explains the market itself.

Database figures are from VendorVerify as of September 29, 2026. This isn't medical advice; thymulin is sold for research use only, and we found no approval for it as a drug.