Thymulin Peptide: Zinc, T-Cells and What the Evidence Shows

Research use only. Nothing on this page is medical advice. Thymulin isn’t approved for human use.

Thymulin is a nine-amino-acid hormone made by the thymus, and it only works when it carries one zinc ion. In mice it calms inflammation, and a 2026 Nature Communications study found it restored antitumor T-cell responses in aged mice. No clinical trial of thymulin has been published, and no regulator has approved it.

Also called

Serum thymic factor, FTS, facteur thymique sérique

Sequence

pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn, 9 amino acids

Made by

Epithelial cells of the thymus

Needs

One zinc ion per molecule. Without zinc it has no activity

Serum half-life

About 10.3 minutes, as reported in a 2024 review

Human trials

None. Human data are observational

FDA status

Not approved

WADA 2026

S0 catch-all: bans any substance with no regulatory approval

What is thymulin?

Thymulin is a nonapeptide hormone made only by the epithelial cells of the thymus, the organ where T-cells mature (12, 13). French researchers isolated it from pig serum and sequenced it in 1977, which is why older papers call it FTS or facteur thymique sérique (14). The thymus sits behind the breastbone, between the lungs and in front of the heart. It isn’t the thyroid, which is the butterfly-shaped gland in your neck.

Thymulin levels peak in early life and fall with age (12, 2). The gland itself shrinks too. In a CT study of 2,540 people with a mean age of 58.9, 74% showed complete fatty replacement of the thymus. Women had less fatty change than men between ages 40 and 69, and smoking and a high BMI went with more (15).

Thymulin vs thymalin, thymosin and thymopoietin

The names blur together in forums and product copy. Thymulin is a single defined peptide. Thymalin is a calf thymus extract, and the thymosins are different molecules.

Why does thymulin need zinc?

Thymulin has no biological activity without a zinc ion bound to it, at one zinc per molecule (12). That makes its activity depend on how much zinc you have. Two human studies show it.

• Zinc depletion, 1988. Prasad’s group studied mildly zinc-deficient people: two volunteers on a zinc-restricted diet, six adults with sickle cell anemia and six without. Serum thymulin activity fell with mild zinc deficiency even though plasma zinc was normal, and zinc supplementation corrected it. In the depleted volunteers the T4/T8 ratio fell, and it recovered with zinc (16).
• Older adults, 1993. Boukaïba’s group gave low-dose zinc to 44 institutionalized older adults in a 16-week crossover study. Serum thymulin activity partly recovered (17).

Plasma zinc is a poor marker of mild deficiency. The 1988 study diagnosed it from zinc in lymphocytes, granulocytes and platelets. More zinc isn’t better, because high intake can cause copper deficiency, and the NIH sets an upper limit of 40 mg a day for adults from all sources (18). A clinician can test your status. Neither study gave people thymulin itself.

What does thymulin do in the body?

• It shapes T-cells. It drives T-cell differentiation inside and outside the thymus and changes the surface markers CD3, CD4 and CD8 (12, 13).
• It talks to the pituitary. In a rat pituitary preparation, thymulin with zinc stimulated ACTH release at picomolar levels (19). Reviews describe it as a hypophysiotropic peptide, one that acts on the pituitary (20).
• It calms inflammation in animals. The table below lists the models.

What did the 2026 Nature Communications study find?

Kanemaru and colleagues found more pro-inflammatory myeloid cells in aged mice and aged humans, cells that make IL-1α, IL-1β, IL-6 and TNF-α and sit in breast tumors. Parabiosis experiments showed that a circulating, non-bone-marrow factor from young mice suppressed them. The factor was thymulin, which acts by inhibiting NF-κB signaling (2).

Given to aged tumor-bearing mice, thymulin restored antitumor T-cell responses, improved tumor control and survival, and sensitized tumors to anti-PD-L1 therapy in an age-dependent manner (2). It’s a mouse result. No one has given thymulin to a patient with cancer.

What does thymulin research show, model by model?

Every row except the last is animal work. Thymulin breaks down fast, so labs use nanoparticles, regulatable adenoviral gene delivery that secretes it over the long term (21), or analogs such as PAT, which matched dexamethasone and indomethacin against inflammatory pain in rats (22).

Is thymulin proven in humans?

No. A 2024 review says thymulin preparations have not advanced into approved clinical trials, and the human literature is observational: biomarker associations in immunodeficiency, acute lymphoblastic leukemia and Crohn’s disease (12, 13). ClinicalTrials.gov lists no thymulin trial.

Three problems hold it back. The peptide’s serum half-life is about 10.3 minutes, it is structurally unstable and breaks down enzymatically, and the cell-surface receptors that carry its signal remain largely uncharacterized (12).

Thymulin peptide dosage: is there one?

There is no human dose. No trial has tested thymulin in people, and the animal studies use different routes, from injections to nanoparticles to gene delivery, so their numbers don’t translate.

The pain studies show why more isn’t better. In rats, low doses caused hyperalgesia through prostaglandin E2 and cytokines (9), and high doses reduced it (8). The only intervention with human data is correcting zinc deficiency, covered above.

Thymulin and cancer, aging, hair and autoimmune disease

Does thymulin help with cancer?

Only in mice so far, where it sensitized tumors to anti-PD-L1 therapy (2). A 2023 review says the evidence on how thymic function shapes patients’ responses to cancer therapy remains unsatisfactory (13).

Does thymulin slow aging?

No human data say so. Thymulin declines with age, and the 2026 mouse study ties that decline to age-related inflammation (2). Nobody has tested whether replacing it helps older people.

Is thymulin good for hair growth?

No hair-growth study of thymulin turned up in PubMed or Europe PMC. The claim comes from seller copy, not from research.

Does thymulin help autoimmune disease?

In a mouse model of relapsing-remitting multiple sclerosis and in mouse type 1 diabetes it reduced symptoms and cytokines (5, 6). Both are animal results.

Thymulin safety and side effects

No human safety data exist. The animal papers report no serious toxicity, and one review calls the safety of thymic peptides consistent even at high concentrations (12). Two findings give pause. In rats, 3 days of thymulin injections lowered intrinsic-pathway clotting factors (11), and in the pain studies low doses made animals more sensitive (9). Neither has been tested in people.

Anyone with a clotting disorder, on anticoagulants, pregnant or breastfeeding, or with an immune condition should talk to a clinician before using any unapproved peptide.

Is thymulin approved or banned in sport?

FDA has not approved thymulin, and it doesn’t appear on FDA’s list of bulk substances that may present significant safety risks (23). On WADA’s 2026 List, S0 bans any substance with no regulatory approval for human therapeutic use, which covers thymulin (24).

Can you buy thymulin?

Laboratory catalog suppliers such as Cayman Chemical list thymulin acetate hydrate for research. Two things matter on any certificate. A purity figure doesn’t show whether the peptide carries zinc, and without zinc it’s inactive. So look for identity confirmed by mass spectrometry and a lot number that matches your vial. Our guide to verifying a peptide COA explains each step, and best peptide vendors compares sellers.

Thymulin FAQ

Keep researching: the full list of peptides, Khavinson peptides, the Wolverine stack and the best peptides by goal.

References