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Natural thymus peptideMostly animalNot FDA approved

Thymulin

Thymulin (zinc bound serum thymic factor)

Last reviewed October 27, 2026 · 24 sources · Written for general readers · Compare with another compound →

The bottom line

Thymulin is a tiny hormone made by the thymus gland, and it only works when it holds a zinc atom.[1][2] It is promoted for hair growth, but the only hair evidence is one study of human hair follicles kept alive in a lab dish, and no trial has tested it on anyone's scalp.[3] Its immune, pain and anti inflammatory effects come from animal and lab studies, so what happens when a person takes it, good or bad, is basically unknown.[1][4]

Where the evidence stands

What it is

Thymulin is a hormone made only by the lining cells of the thymus, a gland behind the breastbone that trains immune cells called T cells. It was first described in the 1970s.[1]

It is a small peptide of 9 amino acids. The peptide by itself is called nonathymulin.[5] It only works when bound to zinc, and scientists named the zinc bound, active form thymulin.[2]

Blood levels change with age. In 93 healthy people from newborns to age 80, levels peaked in children aged 5 to 10, fell from the teen years to a low around age 36, and then stayed steady.[6] This natural decline is part of why it is marketed as an anti aging peptide.

It is also promoted for hair growth, but the only hair research we found was done on hair follicles in a lab dish. The authors of that study noted that thymus products have long been claimed to grow hair without convincing proof.[3]

Name
Thymulin (Thymulin (zinc bound serum thymic factor))
Other names
FTS-Zn, serum thymic factor, facteur thymique sérique, nonathymulin, thymulin acetate
Type
Natural thymus peptide
Sequence
pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn
CAS number
63958-90-7
Formula
C33H54N12O15
Molecular weight
About 858.9 g/mol (peptide without zinc)

What it does in the body

Thymulin is a natural hormone released by the thymus into the blood. Its main known job is to help immature T cells, a type of white blood cell, develop and work properly, and it needs a zinc atom to be active.[1][2] It also talks to the brain and hormone glands, which researchers call the thymus and neuroendocrine link.[7]

This is the biology, area by area. A change measured in the body, like a higher blood level, does not always mean a person feels a benefit. The claims check below covers that.

Immune system

Measured in people

Thymulin helps T cells mature and acts on other immune cells in animal and lab studies.[1] In people, its own activity depends on zinc: in 14 people with mild zinc shortage, thymulin activity fell and returned to normal with zinc pills.[8] In 27 people with Crohn's disease, zinc pills raised blood thymulin activity in the higher zinc group.[9] In 18 children with Down syndrome, two rounds of zinc pills sharply raised active thymulin, raised T cell counts and were linked to fewer infections.[10] These people were given zinc, not thymulin.

Aging immune system

Seen in animals

Natural blood levels fall from childhood to a low by the mid thirties.[6] In old mice, giving thymulin calmed age related inflammation from immune cells called myeloid cells and helped the immune system attack tumors, and in immune cells taken from old mice it lowered inflammatory signals.[4]

Inflammation and pain

Seen in animals

In rats with inflamed paws, thymulin given for 21 days reduced pain sensitivity and swelling and lowered inflammatory signals such as TNF alpha and IL-6 in the spinal cord.[11] In mice with repeated bacterial toxin exposure, it reduced fever and inflammatory signals in the blood.[12] Reviews note that very low amounts made pain worse in rats while higher amounts reduced it.[13]

Hormones and brain

Seen in animals

Thymulin appears to act on the pituitary gland and other hormone glands, and growth hormone in turn raises thymulin. In aged dogs given growth hormone for a month, blood thymulin rose in every treated dog.[7][14] In mice born without a thymus, gene therapy to restore thymulin helped prevent some hormone and reproductive problems.[1]

Lungs

Seen in animals

In animal models of allergic asthma, delivering the thymulin gene with tiny particles reversed key lung changes.[15] Reviews describe similar calming effects in other experimental lung disease models.[16]

Blood sugar

Seen in animals

In mice with chemically induced type 1 diabetes, long term thymulin treatment reduced some of the damage and lowered inflammatory signals.[17] No human study has looked at this.

Skin and hair

Lab finding

In human scalp hair follicles kept alive in a dish, thymulin kept follicles in their growth phase longer, increased dividing cells and reduced dying cells.[3] No one has tested this on a living scalp.

How it works

Thymulin's main known role is as a signal from the thymus to the immune system.

  • It needs zinc. When zinc was stripped out, the hormone stopped working, and adding zinc back turned it on again, best at one zinc atom per peptide.[2]
  • In a 2026 study, thymulin calmed inflammatory immune cells called myeloid cells by blocking a key inflammation switch inside them called NF kappa B.[4]
  • In rats, thymulin and a thymulin related peptide lowered several inflammatory signals, including IL-1 beta, IL-6 and TNF alpha.[18][11]
  • It seems to interact with the hormone system, and researchers think it may act on the pituitary gland.[1][7]
  • In human scalp hair follicles grown in a dish, it kept follicles in their growth phase longer, increased dividing cells and reduced dying cells.[3]

Almost all of this comes from animal and lab work, not from people taking thymulin.

What the research shows

We keep animal and human evidence apart. A result in animals is a reason to study something in people, not proof that it works in people.

Animal and lab studies

Animal and lab dish results only

  • In rats with inflammation caused by bacterial toxin, a thymulin related peptide reduced pain sensitivity in a dose dependent way, prevented fever and lowered inflammatory signals in the liver.[18]
  • In rats with long lasting paw inflammation, thymulin given into the belly cavity for 21 days reduced pain and swelling and calmed immune cells in the spinal cord.[11]
  • In mice given repeated bacterial toxin, free thymulin and thymulin carried on tiny particles both reduced fever, cell death and inflammatory signals in the blood.[12]
  • In old mice, thymulin boosted immune attack on breast tumors, improved tumor control and survival, and helped tumors respond to an immunotherapy drug. The effects were small in young mice.[4]
  • In mice born without a thymus, gene therapy to restore thymulin helped prevent some hormone and reproductive problems, and in animal models of allergic asthma, thymulin gene therapy reversed key features of the disease.[1][15]
  • Hair: scalp follicles from three human donors were kept alive in a dish. Thymulin made hair shafts grow longer than untreated follicles, but responses varied a lot. Thymosin beta 4 and thymosin alpha 1 did not help hair growth in the same test.[3]

Limit: The hair finding comes from follicles kept alive in a dish for about nine days, and the other results come from rodents, which often do not predict effects in people.

Human studies

Almost no human data, and none for hair

  • We found no study that gave thymulin to people for hair loss or hair growth.[3]
  • Two brief one page reports from 1982 and 1985 describe giving thymulin to people with immune deficiency. We could not access their results, and they were not large controlled trials.[19][20]
  • In a study of 14 people, mild zinc shortage lowered the activity of their own thymulin, and zinc supplements brought it back to normal along with several immune cell measures. These people were given zinc, not thymulin.[8]
  • In a randomized, placebo controlled study of 27 people with Crohn's disease in remission, three months of zinc pills raised blood thymulin activity only in the higher zinc group. Immune cell counts did not change. Again, no one was given thymulin.[9]
  • In 13 older adults found to be low in zinc, zinc supplements significantly raised blood thymulin activity and restored some immune measures.[21]
  • In a before and after study of 18 children with Down syndrome, two 2 month rounds of zinc pills sharply raised active thymulin in the blood and raised T cell counts, and repeat infections became less common. There was no comparison group, and no one was given thymulin.[10]
  • In 93 healthy people tested from birth to age 80, natural thymulin levels peaked in childhood and fell to a low by the mid thirties.[6]
  • In a 2026 study, thymulin was added to immune cells taken from old mice in a dish and reduced inflammatory signals. The human blood samples in that study were only measured, not treated, so no person was given the peptide.[4]

Limit: No controlled trial has tested thymulin in people for any use, so its effects and side effects in people are unknown.

Claims check

The most common claims about this compound, and what studies actually found. Verdicts rate the evidence, not whether you should use it.

Regrows hair

Only in animals

Scalp hair follicles from three human donors were kept alive in a dish for about nine days. Thymulin made hair shafts grow longer than untreated follicles, but responses varied a lot from donor to donor.[3] No study has applied thymulin to a living scalp or given it to people with hair loss.

Boosts the immune system

Only in animals

Thymulin acts on immune cells in animal and lab studies, and a review describes human use as a future goal rather than something already tested.[1] Two brief reports from 1982 and 1985 describe giving it to people with immune deficiency, but they were not controlled trials and their results could not be checked.[19][20]

Reduces inflammation and pain

Only in animals

In rats with inflamed paws, three weeks of thymulin reduced pain and swelling.[11] In other rat work, a thymulin related peptide reduced pain from inflammation about as well as a steroid or an anti inflammatory drug.[18] A review notes that very low amounts increased pain in rats.[13] No human study has tested this.

Reverses immune aging

Only in animals

In old mice, thymulin calmed age related inflammation and helped the immune system fight breast tumors, with small effects in young mice. In immune cells taken from old mice, it reduced inflammatory signals.[4] Lower levels with age are well documented in people, but no one has shown that giving thymulin reverses aging.[6]

Helps asthma and lung inflammation

Only in animals

In animal models of allergic asthma, delivering the thymulin gene with tiny particles reversed key lung changes.[15] This used gene therapy, not the peptide sold online, and has not been tested in people.

Protects against sepsis and diabetes

Only in animals

In mice exposed again and again to bacterial toxin, thymulin reduced fever, cell death and inflammatory signals.[12] In mice with chemically induced diabetes, it reduced several signs of damage.[17] Neither has been tested in people.

Known risks and side effects

  • Unknown human safety. No controlled human trial has reported side effects, and a 2014 review described human use as a future goal rather than something already tested.[1]
  • Effects can flip with amount. In rats, very low amounts of thymulin made pain worse while higher amounts eased it, so effects in people cannot be predicted.[13]
  • Acts on the immune and hormone systems. Thymulin changes how immune cells behave and interacts with hormone glands. How that plays out in people with immune, autoimmune or hormone conditions has not been studied.[1][4][7]
  • Unregulated online products. Thymulin acetate sits in FDA's Category 3, substances nominated for compounding without enough supporting information, so there is no FDA check on products sold online for content, purity or sterility.[22]
  • Homeopathic versions. A homeopathic pellet labeled with nonathymulin appears in the federal DailyMed label database as an unapproved homeopathic product that FDA has not evaluated for safety or effectiveness.[23]

Regulatory status

Today: Thymulin is not an approved drug in the United States. Thymulin acetate is in Category 3 of FDA's compounding nomination lists, meaning it was nominated without adequate support.[22] WADA's 2027 list does not name thymulin, but its S0 rule bans any substance with no current government approval for human use.[24]

  1. FDA's updated compounding category lists placed thymulin acetate in Category 3, nominated without adequate support.[22]
  2. WADA's 2027 Prohibited List takes effect, keeping its S0 ban on unapproved substances.[24]

Sources

  1. Reggiani PC, Schwerdt JI, Console GM, Roggero EA, Dardenne M, Goya RG. Physiology and therapeutic potential of the thymic peptide thymulin. Curr Pharm Des. 2014;20(29):4690-4696. PMID 24588820
  2. Dardenne M, Pléau JM, Nabarra B, Lefrancier P, Derrien M, Choay J, Bach JF. Contribution of zinc and other metals to the biological activity of the serum thymic factor. Proc Natl Acad Sci U S A. 1982;79(17):5370-5373. PNAS 1982
  3. Meier N, Langan D, Hilbig H, Bodó E, Farjo NP, Farjo B, Armbruster FP, Paus R. Thymic peptides differentially modulate human hair follicle growth. J Invest Dermatol. 2012;132(5):1516-1519. PMID 22402437
  4. Kanemaru H, Luong S, Yamamoto Y, Mizukami Y, et al. Thymulin restrains age-associated myeloid inflammation and enhances cancer immunotherapy. Nat Commun. 2026;17(1):6534. PMID 42481458
  5. U.S. Food and Drug Administration and NCATS. Global Substance Registration System: nonathymulin (UNII 9H198D04WL). FDA GSRS
  6. Consolini R, Legitimo A, Calleri A, Milani M. Distribution of age-related thymulin titres in normal subjects through the course of life. Clin Exp Immunol. 2000;121(3):444-447. DOI 10.1046/j.1365-2249.2000.01315.x
  7. Goya RG, Brown OA, Pléau JM, Dardenne M. Thymulin and the neuroendocrine system. Peptides. 2004;25(1):139-142. PMID 15003367
  8. Prasad AS, Meftah S, Abdallah J, Kaplan J, Brewer GJ, Bach JF, Dardenne M. Serum thymulin in human zinc deficiency. J Clin Invest. 1988;82(4):1202-1210. J Clin Invest 1988
  9. Brignola C, Belloli C, De Simone G, et al. Zinc supplementation restores plasma concentrations of zinc and thymulin in patients with Crohn's disease. Aliment Pharmacol Ther. 1993;7(3):275-280. DOI 10.1111/j.1365-2036.1993.tb00098.x
  10. Franceschi C, Chiricolo M, Licastro F, Zannotti M, Masi M, Mocchegiani E, et al. Oral zinc supplementation in Down's syndrome: restoration of thymic endocrine activity and of some immune defects. J Ment Defic Res. 1988;32(Pt 3):169-181. PMID 2971113
  11. Nasseri B, Zaringhalam J, Daniali S, et al. Thymulin treatment attenuates inflammatory pain by modulating spinal cellular and molecular signaling pathways. Int Immunopharmacol. 2019;70:225-234. PMID 30851702
  12. Novoselova EG, Lunin SM, Glushkova OV, et al. Thymulin, free or bound to PBCA nanoparticles, protects mice against chronic septic inflammation. PLoS One. 2018;13(5):e0197601. PMID 29795607
  13. Dardenne M, Saade N, Safieh-Garabedian B. Role of thymulin or its analogue as a new analgesic molecule. Ann N Y Acad Sci. 2006;1088:153-163. PMID 17192563
  14. Goff BL, Roth JA, Arp LH, et al. Growth hormone treatment stimulates thymulin production in aged dogs. Clin Exp Immunol. 1987;68(3):580-587. PMID 3652525
  15. da Silva AL, de Oliveira GP, Kim N, et al. Nanoparticle-based thymulin gene therapy therapeutically reverses key pathology of experimental allergic asthma. Sci Adv. 2020;6(24):eaay7973. DOI 10.1126/sciadv.aay7973
  16. Santos M, Henriques-Coelho T, Leite-Moreira A. Immunomodulatory role of thymulin in lung diseases. Expert Opin Ther Targets. 2010;14(2):131-141. PMID 20055713
  17. Novoselova EG, Glushkova OV, Lunin SM, et al. Thymulin and peroxiredoxin 6 have protective effects against streptozotocin-induced type 1 diabetes in mice. Int J Immunopathol Pharmacol. 2021;35:20587384211005645. PMID 33779346
  18. Safieh-Garabedian B, Dardenne M, Pléau JM, Saadé NE. Potent analgesic and anti-inflammatory actions of a novel thymulin-related peptide in the rat. Br J Pharmacol. 2002;136(6):947-955. DOI 10.1038/sj.bjp.0704793
  19. Dardenne M, Bordigoni F, Bene MC, Bach JF. Clinical use of thymulin (FTS-Zn) in immunodeficiency syndromes. Int J Immunopharmacol. 1982;4(4):368. DOI 10.1016/0192-0561(82)90396-4
  20. Faure G, Béné MC, Caranzan F, Gérard A, Braun D, Conroy T. Immunopharmacokinetics of a single dose of thymulin in immunodeficient adults. Int J Immunopharmacol. 1985;7(3):312. DOI 10.1016/0192-0561(85)90214-0
  21. Prasad AS, Fitzgerald JT, Hess JW, Kaplan J, Pelen F, Dardenne M. Zinc deficiency in elderly patients. Nutrition. 1993;9(3):218-224. PMID 8353362
  22. U.S. Food and Drug Administration. Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the FD&C Act (category lists). Updated May 14, 2026. FDA 503A category lists
  23. U.S. National Library of Medicine. DailyMed search results for nonathymulin (unapproved homeopathic human OTC label). DailyMed
  24. World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2027. In force January 1, 2027. WADA 2027 List, S0
Medical disclaimer

This page is educational information only. It is not medical advice and does not replace care from a licensed medical provider. Do not use this page to decide whether to take any substance. Talk to a licensed medical provider first.

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