At a Glance
| Feature | Detail |
|---|---|
| Name / structure | Thymulin, zinc-thymulin (FTS-Zn); nonapeptide pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn bound to one zinc ion |
| Origin | Described by Jean-François Bach and Mireille Dardenne (Paris) as “facteur thymique sérique” |
| Mechanism | Thymic hormone that promotes T-cell differentiation and function; anti-inflammatory and neuroendocrine effects in animals; inactive without zinc |
| Used for | Immune “rejuvenation”, inflammation and pain (animal data), hair loss (topical) |
| Route | Subcutaneous injection (grey market); topical scalp spray or foam |
| Typical dose range | No validated dose. Practice: 1–60 mcg or 1–5 mg SC daily, ~20-day courses; topical 0.0005 % |
| Evidence level | Limited: solid physiology and animal data, one tiny 1980s human report, one uncontrolled topical study |
| Regulatory status | Not approved anywhere; FDA 503A category 3 (thymulin acetate, nominated without adequate support); WADA 2026: S0 (non-approved substance), prohibited at all times |
Thymulin is one of the best-characterised thymic hormones and one of the least tested as a treatment. Its biology is elegant. The thymus secretes it, zinc switches it on, and its decline tracks the shrinking of the thymus with age. That makes it an obvious candidate for anyone thinking about immune ageing.
My verdict: thymulin is a fascinating biomarker with a thin treatment record. If your interest is immune ageing, the most evidence-based move is to check zinc status, because thymulin activity depends on it. Injected thymulin has almost no human data, and topical thymulin for hair has one uncontrolled study.
How it works
Thymulin is produced by thymic epithelial cells. It binds zinc in a 1:1 ratio, and only the zinc-bound form is biologically active; antibodies raised against the active hormone recognise only the zinc-coupled molecule [2]. In T-cell biology it promotes the maturation of T-cell precursors and influences several T-cell subsets, with the effect on suppressor (regulatory) function described as the most striking in early work [1].
Thymulin also talks to the nervous and endocrine systems. In animals it influences pituitary hormones [9] and has dose-dependent effects on pain: very low doses increase pain sensitivity, while higher doses, or an analogue without that effect, reduce inflammatory pain and cytokine levels after endotoxin [8]. A 2026 study found that thymulin suppressed age-associated inflammatory activity in myeloid cells via NF-kB and improved the response to checkpoint immunotherapy in aged mice [6]. These are animal and cell findings.
In people, plasma thymulin is detectable at birth, peaks at ages 5 to 10, falls through adolescence and reaches a low plateau by the mid-thirties [3]. Low thymulin activity is found in zinc deficiency and several diseases, and it rises when zinc is replaced [7].
What the evidence shows
Human data
| Study | Design | n | Intervention | Finding |
|---|---|---|---|---|
| Consolini 2000 [3] | Cross-sectional, healthy people from birth to 80 years | 93 | None (measurement) | Thymulin peaks at 5–10 years, falls from adolescence, low plateau from about 36 years |
| Dokhelar 1983 [5] | Laboratory study plus 4 cancer patients | 4 treated | Synthetic FTS 10 mcg/kg IV every 3 days | NK-cell activity rose in 2 patients with low baseline values and fell in 2 with normal or high values |
| Brignola 1993 [7] | Randomised, placebo-controlled, Crohn’s disease in remission | 27 | Zinc sulphate 60 or 200 mg/day for 3 months | Plasma zinc and thymulin activity rose only at 200 mg/day |
| Vickers 2017 [10] | Uncontrolled, androgenetic alopecia | 18 | 0.0005 % zinc-thymulin spray, 1–2 mL twice daily, 4–10 months | Global improvement significant only after at least 6 months; the author directs the company that makes the product |
That is close to the full human treatment record. There are no modern controlled trials of injected thymulin, and the hair study has no placebo arm.
Animal data
Thymulin gene therapy corrected hormonal abnormalities in thymus-deficient mice, and thymulin and an analogue reduced inflammatory pain in rodents [4][8]. The review by the La Plata group presents these findings as a basis for therapy, not as evidence of it [4].
Dosing
For informational purposes only — this summarises doses used in research and practice; it is not a prescription or individual medical advice.
| Goal | Dose | Route | Frequency / timing | Cycle length | Basis |
|---|---|---|---|---|---|
| Immune modulation (research) | 10 mcg/kg (about 0.7 mg at 70 kg) | IV | Every 3 days | Short course | Trial (4-patient report) [5] |
| Raising low thymulin via zinc | Zinc sulphate 200 mg | Oral | Daily | 3 months | Trial [7] |
| Hair loss | 0.0005 % zinc-thymulin solution, 1–2 mL | Topical spray to scalp | Twice daily | At least 6 months | Uncontrolled study [10] |
| Immune support, microgram protocol | 1–60 mcg | SC | Daily (one clinic: 20 days on, 10 off, zinc checked first) | About 20 days, repeated | Practice protocol (peptide-db, HealthRx clinic page) |
| Immune support, milligram protocol | 1–2 mg (sources up to 5 mg) | SC | Daily | About 20 days, 2–3 times a year | Practice protocol (Peptide Catalog, OnePin) |
| Hair stacks | Topical thymulin plus GHK-Cu, minoxidil or finasteride | Topical | Daily | Months | Anecdotal (r/tressless) |
The two injection protocols differ by a factor of more than 1,000, and neither comes from a trial. One protocol site argues that milligram doses are thymalin doses applied to the wrong compound (Jacked Forums). The only human injection data used about 0.7 mg IV every third day in four patients [5]. Given that very low doses increased pain sensitivity in animals [8], the dose question is not academic. Many practitioners pair thymulin with zinc, and checking zinc status first is the one step that rests on human data [7].
For injection technique, see the peptide injection guide.
What people report: what works and what doesn’t
Reported to work
- Topical use for hair: some users report less shedding or new fine hairs after 8 to 12 months, almost always alongside minoxidil, finasteride or GHK-Cu (r/tressless).
Mixed or unclear
- Because it is used in stacks, users cannot say which product did what.
- Doubts about whether the peptide penetrates the scalp, and complaints that solutions are unstable and expensive.
Reported not to work, or disappointing
- No dramatic regrowth in any report I found.
- Injected thymulin in long COVID: reports of no benefit, and one of daily diarrhoea after about two months at 15 mg per day, a dose far above anything studied (r/vaccinelonghauler).
What a proper trial would need to show: that injected thymulin at a defined dose improves a clinical immune outcome (vaccine response, infection rate) in older adults compared with placebo and with zinc repletion alone; and for hair, a placebo-controlled study with hair counts.
Safety and side effects
No systematic human safety data exist for injected thymulin. Early human use did not report toxicity, and its discoverers considered it non-toxic [1], but that rests on very little exposure. Points of concern:
- Pain sensitivity: low doses caused hyperalgesia in animals [8].
- Immune modulation cuts both ways: in the 1983 report, NK activity fell in patients whose baseline was normal or high [5]. Effects in autoimmune disease are unknown.
- Neuroendocrine effects: thymulin influences pituitary hormones in animals [9]; the human relevance is unknown.
- Dose confusion with thymalin, and unknown purity, content and sterility of grey-market vials.
- Zinc: high-dose zinc over months can cause copper deficiency, so zinc repletion should follow measured levels.
Pregnancy, breastfeeding, active cancer, transplant recipients and people on immunosuppressants: no data, so avoid it outside a trial.
Legal and regulatory status
- United States. Not approved. FDA’s 503A bulk-substance nominations list places thymulin acetate in category 3 (nominated without adequate support), so it has no legitimate compounding route (FDA list). It does not appear on FDA’s significant-safety-risk list.
- EU and Germany. No marketing authorisation. Cosmetic topical products containing thymulin exist; injectable thymulin for human use would be an unauthorised medicine.
- Sport. As a non-approved substance, thymulin falls under WADA 2026 class S0, prohibited at all times [11].
How it fits
Thymulin sits next to two better-studied thymic peptides on this site. Thymosin alpha-1 is licensed in some countries and has randomised trials in hepatitis B and sepsis. Thymalin and the Khavinson thymus bioregulators are covered under peptide bioregulators. For thymic shrinkage and what can be done about it, see thymic involution and immune ageing. Of these, thymulin has the most elegant biology and the least clinical evidence.
Related Articles
- Thymic Involution and Immune Aging
- Thymosin Alpha-1: Overview
- Thymus Function and T-Cell Health
- Zinc Supplement Guide: Immune Function and Wound Healing
- Peptides for Hair Loss
Frequently asked questions
What is thymulin?
Thymulin (formerly facteur thymique sérique, FTS) is a nonapeptide hormone secreted by thymic epithelial cells. It needs zinc to be biologically active and helps T cells differentiate. Its levels rise in childhood and fall from adolescence onward.
Is thymulin the same as thymalin?
No. Thymulin is a single defined nine-amino-acid peptide. Thymalin is a Russian calf-thymus extract (a mixture of peptides) used at milligram doses. Many online protocols mix up the two, which is one reason thymulin doses quoted online range from micrograms to milligrams.
What dose of thymulin do people use?
There is no validated human dose. Practice sources quote anything from 1–60 mcg daily to 1–5 mg daily under the skin, usually in courses of about 20 days. A topical scalp spray at 0.0005% (1–2 mL twice daily) was used in a small uncontrolled hair-loss study.
Does thymulin help hair loss?
An uncontrolled study of 18 people using a 0.0005% zinc-thymulin spray reported improvement only after at least 6 months, and its author directs the company behind the product. There is no placebo-controlled trial.
Can zinc raise thymulin?
In zinc-deficient people, yes. In a randomised study in Crohn's disease, 200 mg per day of zinc sulphate for 3 months restored low plasma zinc and thymulin activity, while 60 mg did not. Checking and correcting zinc status is the evidence-based first step.
References
- Bach JF, Dardenne M. Thymulin, a zinc-dependent hormone. Med Oncol Tumor Pharmacother. 1989. PMID: 2657247. https://pubmed.ncbi.nlm.nih.gov/2657247/
- Dardenne M, Savino W, Berrih S, et al. A zinc-dependent epitope on the molecule of thymulin, a thymic hormone. Proc Natl Acad Sci U S A. 1985. PMID: 2413455. https://pubmed.ncbi.nlm.nih.gov/2413455/
- Consolini R, Legitimo A, Calleri A, et al. Distribution of age-related thymulin titres in normal subjects through the course of life. Clin Exp Immunol. 2000. PMID: 10971509. https://pubmed.ncbi.nlm.nih.gov/10971509/
- Reggiani PC, Schwerdt JI, Console GM, et al. Physiology and therapeutic potential of the thymic peptide thymulin. Curr Pharm Des. 2014. PMID: 24588820. https://pubmed.ncbi.nlm.nih.gov/24588820/
- Dokhelar MC, Tursz T, Dardenne M, et al. Effect of a synthetic thymic factor (facteur thymique serique) on natural killer cell activity in humans. Int J Immunopharmacol. 1983. PMID: 6195118. https://pubmed.ncbi.nlm.nih.gov/6195118/
- Kanemaru H, Luong S, Yamamoto Y, et al. Thymulin restrains age-associated myeloid inflammation and enhances cancer immunotherapy. Nat Commun. 2026. PMID: 42481458. https://pubmed.ncbi.nlm.nih.gov/42481458/
- 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. PMID: 8364132. https://pubmed.ncbi.nlm.nih.gov/8364132/
- Dardenne M, Saade N, Safieh-Garabedian B. Role of thymulin or its analogue as a new analgesic molecule. Ann N Y Acad Sci. 2006. PMID: 17192563. https://pubmed.ncbi.nlm.nih.gov/17192563/
- Goya RG, Brown OA, Pléau JM, et al. Thymulin and the neuroendocrine system. Peptides. 2004. PMID: 15003367. https://pubmed.ncbi.nlm.nih.gov/15003367/
- Vickers ER. An Analysis of the Safety and Efficacy of Topical Zinc-Thymulin to Treat Androgenetic Alopecia. Hair Ther Transplant. 2017 (not indexed in PubMed). https://www.longdom.org/open-access-pdfs/an-analysis-of-the-safety-and-efficacy-of-topical-zincthymulin-to-treat-androgenetic-alopecia-2167-0951-1000147.pdf
- World Anti-Doping Agency. The 2026 Prohibited List (S0), as published in Tractatenblad 2026, 25. https://zoek.officielebekendmakingen.nl/trb-2026-25.html
Disclaimer: This article is for information and education only and is not a prescription or individual medical advice. Thymulin is not an approved medicine.
