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 was first called facteur thymique serique (FTS). It is a hormone of nine amino acids. Only the epithelial cells of the thymus make it. It circulates bound to a zinc ion. The zinc is required. Without it, the peptide has a floppy shape and no biological activity. Jean-Francois Bach's group in Paris characterized it in the 1970s. 12
Thymulin production falls with age as the thymus shrinks. It also falls in zinc deficiency. Researchers have used blood thymulin activity as a sensitive marker of mild zinc deficiency in humans. It recovers when zinc is replaced. The injectable product sold online is a lab-made copy of the peptide. It is usually without the zinc. 2
How it works
Thymulin helps T cells mature inside and outside the thymus. It also modulates their function. The pituitary and the hormones it releases control its secretion. These are growth hormone, prolactin and thyroid hormone. 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 lab-made version also reduce inflammatory pain and brain inflammation. Researchers have proposed gene therapy with a synthetic thymulin gene. It might 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 people were given thymulin for any use. The human literature consists of measuring thymulin activity in blood. There it tracks zinc status. It declines with age and in some immune deficiencies. Claims about restoring immunity in older adults come from mouse experiments. These mostly used gene therapy with a synthetic thymulin gene, 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. Thymulin is a hormone the body makes. It has low activity without zinc. So short-term toxicity in animals has not been a concern in the published work. But no one knows what repeated injection does in people. Dose, immunogenicity and interaction with autoimmune disease are also unknown. 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. 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. The zinc fixes its three-dimensional shape. In people with mild zinc deficiency, thymulin activity in blood drops. It comes back with zinc supplements. 2
Is thymulin the same as thymalin or thymosin?
No. Thymulin is a single defined hormone of nine amino acids. Thymalin is a crude extract of calf thymus. It holds many peptides. Thymosin alpha-1 and thymosin beta-4 are separate, larger peptides. They were also first isolated from thymus extract. 1