Thymulin
Thymic immune peptide
Also Facteur thymique serique, FTS, Serum thymic factor, Thymulin peptide, Zinc-thymulin, Zn-FTS
- Evidence
- CAnimal and cell studies
- FDA status
- Not approvedas of 2026-10-26
- Route
- Injection
- Studies cited
- 0 human2 animal or cell
Sold to rebuild the immune system as people age. It is a real body hormone, but no one has tested it as a drug in people.
Sold for
Thymulin is sold as an anti-aging immune peptide that restores a shrinking thymus and rebalances T cells.
Studies say
Thymulin is a real thymic hormone whose biology is well described in animals, but no human trial has tested giving it as a drug, which puts it at C.
Why grade C. The literature on thymulin is physiological: how the thymus makes it, how zinc activates it, and what it does in rodent models of aging, inflammation and pain. Human data are limited to measurements of thymulin activity in blood as a marker of zinc status; there are no interventional trials of giving thymulin to people. Grade C for the immune-restoration use it is sold for. 12
FDA. Thymulin is not approved by the FDA for any use and is sold as a research chemical. No pharmaceutical company has brought it through clinical development. 1
Written from 2 cited sources. Fact-checked 2026-10-27: 9 claims checked, 2 corrected. Last refreshed 2026-10-27. Not physician reviewed.
What this means for you
- What people take it for
- Anti-aging and immune support.
- Can a US doctor prescribe it?
- No. It is not approved and is sold as a research chemical.
- Properly tested in people?
- Not properly: animal or lab studies, or small uncontrolled human reports. No human trial has given it as a drug.
Evidence checklist
- Randomised controlled trial No trial has given it to peopleno
- Human study over 100 people No interventional human studyno
- More than one research group Animal and lab work onlyno
- Clinical outcomes, not surrogate markers Blood activity levels as zinc marker onlyno
- Human safety data beyond case reports No human safety datano
Drawn from the cited studies below. A dash means the sources give no information.
What it is
Thymulin, originally called facteur thymique serique (FTS), is a nine-amino-acid hormone produced only by the epithelial cells of the thymus. It circulates bound to a zinc ion, and the zinc is required: without it the peptide has a floppy shape and no biological activity. It was characterized in the 1970s by Jean-Francois Bach's group in Paris. 12
Thymulin production falls with age as the thymus shrinks, and also falls in zinc deficiency. Blood thymulin activity has been used in research as a sensitive marker of mild zinc deficiency in humans, recovering when zinc is replaced. The injectable product sold online is a synthetic copy of the peptide, usually without the zinc. 2
How it works
Thymulin promotes the differentiation of T cells inside and outside the thymus and modulates their function. Its secretion is under control of the pituitary and the hormones it releases (growth hormone, prolactin, thyroid hormone), and in turn thymulin appears to act back on the pituitary, so it sits in a loop between the immune and endocrine systems. In rodents, thymulin and a synthetic analog also reduce inflammatory pain and brain inflammation, and gene therapy with a synthetic thymulin gene has been proposed to prevent some of the endocrine and metabolic changes seen in thymus-deficient animals. 1
What human research shows
There are no published trials in which thymulin was administered to humans for any indication. The human literature consists of measuring thymulin activity in blood, where it tracks zinc status and declines with age and in some immune deficiencies. Claims about restoring immunity in older adults come from mouse experiments, mostly involving gene therapy with a synthetic thymulin gene and not injected peptide. 12
| Study | Model | Finding |
|---|---|---|
| Reggiani 2009 review (Ann N Y Acad Sci) | Review of rodent and in vitro studies | Summarizes thymulin's zinc dependence, its two-way link with the pituitary, anti-inflammatory and analgesic effects in the rodent brain, and thymulin gene therapy in thymus-deficient animals. 1 |
| Prasad 2007, zinc and host defense (J Nutr) | Review of human and animal studies | Thymulin activity depends on zinc and falls in human zinc deficiency, recovering with repletion. 2 |
Safety
No human safety data exist. Because thymulin is an endogenous hormone with low activity in the absence of zinc, acute toxicity in animals has not been a concern in the published work, but nothing is known about repeated injection in people, dose, immunogenicity, or interaction with autoimmune disease. 1
Questions for your clinician
- Is there any controlled human trial of thymulin?
- Would a zinc status check be more useful than the peptide?
- How does it interact with an autoimmune condition?
Questions people ask
Is thymulin FDA-approved?
No. It has never been studied in a registered clinical trial, and products sold online are labeled for research use. 1
Has thymulin been tested in humans?
Not as a treatment. Human studies measured thymulin levels in blood, mainly as a marker of zinc deficiency and aging. Experiments on restoring immune function used rodents. 12
Why does zinc matter for thymulin?
The peptide is only active when a zinc ion is bound to it, which fixes its three-dimensional shape. In people with mild zinc deficiency, thymulin activity in blood drops and comes back with zinc supplementation. 2
Is thymulin the same as thymalin or thymosin?
No. Thymulin is a single defined nine-amino-acid hormone. Thymalin is a crude extract of calf thymus containing many peptides. Thymosin alpha-1 and thymosin beta-4 are separate, larger peptides that were also first isolated from thymus extract. 1