Identity
Thymulin — historically FTS (facteur thymique sérique, serum thymic factor) — is a thymic hormone, a nonapeptide with one defining peculiarity: it is biologically active only when bound to zinc. The zinc-free peptide is inactive. It is produced by thymic epithelial cells and is involved in T-lymphocyte differentiation and immune regulation.
A naming firewall matters here, because three similar-sounding substances are routinely confused:
- Thymulin (this entry) — the natural zinc-dependent thymic hormone (FTS).
- Thymalin — a thymic extract (a mixture of peptides), a separate entry.
- Thymogen / Thymagen — a synthetic Khavinson cytogen, covered by the bioregulators entry.
These are different substances and should not be treated as synonyms.
Mechanism (as proposed)
Thymulin's endocrinology is genuinely well characterised. As a zinc-dependent thymic peptide, it participates in the maturation and differentiation of T-lymphocytes and in immune regulation. Two facts are consistently reported and central: thymulin activity declines with age (tracking the thymus's own involution), and it depends on zinc — in zinc deficiency, circulating thymulin loses activity, which is one of the links between zinc status and immune function. This is a real mechanism in the literature — but it is biology, not a demonstrated human therapy.
Reading the evidence honestly
The decisive gap is clinical: there is essentially no controlled human trial evidence that administering thymulin — as an injected or "research-peptide" supplement — improves immunity, reverses age-related immune decline, or produces any outcome in healthy people. Real thymic biology is being used to sell an unvalidated product. That is why the marketed use is graded D and the "anti-aging / immune-boost / thymus-regeneration" framing F: the hormone is real, the human evidence for dosing it is not. Thymulin is a research chemical, not a cosmetic, approved drug or proven supplement, and age-related immune concerns are a matter for a doctor.