Thymulin is a naturally occurring nine-amino-acid hormone made mainly by cells in the thymus gland. It only works when bound to zinc, which is unusual among hormones and central to its biology. Researchers have studied it since the 1970s for its role in T-cell development and immune regulation. It is a distinct substance from “Thymalin,” a differently-sourced Russian thymic peptide product that is sometimes confused with it due to similar naming.
Research snapshot
| Category | Current information |
|---|---|
| Peptide category | Naturally occurring zinc-dependent thymic nonapeptide hormone |
| Primary research interest | T-cell development and immune regulation; zinc-deficiency-related immune effects |
| Highest available evidence | Published human observational research (endogenous serum thymulin bioactivity, not administered-dose trials) |
| Human research available | No administered-dose human clinical trials identified; human data concerns measurement of endogenous serum thymulin bioactivity |
| Development status | Not developed into a pharmaceutical drug candidate; exists as a research reagent and endogenous-hormone research subject |
| Regulatory status | Not an approved pharmaceutical product in the jurisdictions reviewed |
| Last reviewed | September 27, 2026 |
Technical identity
| Technical property | Information |
|---|---|
| Primary name | Thymulin |
| Alternative names | FTS (Facteur Thymique Serique), Zinc-thymulin, Zn-FTS; frequently but incorrectly confused online with “Thymalin,” a separate Russian thymic-extract bioregulator product |
| Peptide sequence | pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn (nonapeptide; active form requires a bound zinc ion, “zinc-thymulin”) |
| Amino-acid length | 9 residues |
| Molecular formula | C33H54N12O15 — from a chemical-supplier database listing (ChemicalBook), not independently confirmed against a peer-reviewed or regulatory source |
| Molecular weight | Approximately 858.85 g/mol — same supplier-only sourcing |
| CAS Registry Number | 63958-90-7 (from chemical-database sources). Note: “Thymalin,” a distinct substance, is reported by some peptide-vendor sources under a different CAS (79621-14-0, lower-reliability vendor source) — the two should not be confused. |
| PubChem CID | Not reliably established |
| Chemical modifications | N-terminal pyroglutamate; requires a bound zinc ion for biological activity |
| Peptide class | Zinc-dependent thymic hormone nonapeptide |
| Primary biological target | T-lymphocyte maturation pathways; biological activity is zinc-dependent |
| Developer or originator | Naturally occurring human/mammalian hormone, first described by Bach in 1977 |
| Development status | Not developed as an administered pharmaceutical; research reagent only |
What it is
Thymulin, also called “facteur thymique serique” (FTS) in the original French literature, is a nonapeptide hormone with the sequence pyroglutamyl-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn (commonly written pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn). It was first described by Jean-Francois Bach and colleagues in 1977 as a serum factor with thymic hormone-like activity, and was later shown to require a bound zinc ion for its biological effects — the active form is often written as “zinc-thymulin” or Zn-FTS. It is produced primarily by thymic epithelial cells and circulates in serum, with levels that change with age (declining with thymic involution), zinc status, and health state.
Thymulin is a genuine, well-characterized research peptide from the mainstream international immunology literature, distinct from synthetic drug candidates developed for market approval. It has not been developed into an approved pharmaceutical product in the way thymosin alpha-1 (Zadaxin) or thymalfasin has; the bulk of research on it is preclinical (cell and animal) and observational human research examining its serum levels in various conditions, rather than large interventional human drug trials.
Because zinc is required for thymulin activity, researchers have long been interested in the peptide as one explanation for the immune effects of zinc deficiency, since low zinc status correlates with reduced biologically active thymulin even when total thymulin peptide (including its inactive, zinc-free form) is unchanged. Thymulin has also been examined for effects beyond straightforward immune modulation, including neuroendocrine and circadian interactions with the hypothalamic-pituitary axis, and more recent laboratory work on thymulin analogs designed for anti-inflammatory, neuroprotective applications.
How does it work?
Plain-English explanation
Thymulin helps young immune cells called T cells mature properly in the thymus and supports the activity of mature T cells and natural killer cells elsewhere in the body. Because it needs zinc to function, having enough zinc in the diet or body is part of what keeps this system working normally.
Technical explanation
Thymulin promotes T-lymphocyte differentiation and expression of T-cell surface markers, and modulates cytokine production and NK-cell cytotoxic activity. Its biological activity strictly depends on zinc coordination, which is thought to stabilize a conformation of the peptide required for receptor interaction; the free (non-zinc-bound) peptide is largely inactive. Thymulin also participates in bidirectional signaling with the neuroendocrine system, with reported effects on and from corticotropin-releasing hormone/ACTH pathways, and circulating levels follow age-related thymic involution.
Potential benefits and research applications
T-cell development and immune regulation
What is being investigated: thymulin’s role in normal T-cell maturation and how declining thymulin with age or zinc deficiency may contribute to immune decline. How the effect might occur: direct promotion of T-cell differentiation markers and support of NK-cell function. Evidence: primarily animal and in vitro research plus human observational studies correlating serum thymulin activity with age, zinc status, and immune parameters. Strength: Tier 3-4 for mechanism, Tier 2 for human correlational data. Limitation: observational human data show correlation, not proof that raising thymulin activity therapeutically improves immune outcomes.
Neuroprotective and anti-inflammatory research (thymulin analogs)
What is being investigated: engineered thymulin-related analogs for central nervous system anti-inflammatory and neuroprotective effects. How the effect might occur: proposed modulation of neuroinflammatory signaling. Evidence: laboratory and animal-model research only. Strength: Tier 3-4. Limitation: this is early-stage, mechanism-focused research; no human clinical trials of thymulin or its analogs for neurological indications were identified.
Zinc-deficiency-related immune effects
What is being investigated: whether restoring zinc status normalizes thymulin activity and associated immune function in zinc-deficient states. How the effect might occur: zinc is required to activate the peptide, so correcting deficiency may restore active thymulin levels. Evidence: human observational and some interventional studies of zinc status and thymulin activity. Strength: Tier 2. Limitation: this evidence supports a zinc-nutrition relationship rather than thymulin itself as an administered therapeutic.
What dosage information circulates?
Figures in this section summarize amounts and schedules reported in published research or circulating online. Their inclusion documents what is reported and does not establish that a regimen is verified, safe, effective, or appropriate.
| Reported use or research objective | Route reported | Amount reported | Frequency reported | Reported duration | Evidence or source category |
|---|---|---|---|---|---|
| Any administered human use | Not applicable | No established or reliably sourced dosing information was identified | Not applicable | Not applicable | Not established — human literature is dominated by measurement of endogenous serum thymulin activity, not dose-ranging administration trials |
| Immune and neuroinflammatory models | Injection (route as used in various animal studies) | A single representative, consistently reported dose figure could not be confidently traced to a primary source | Varies by study | Varies by study | Published animal research |
| General “research compound” framing | Subcutaneous injection | Informally suggested protocols, not derived from published human dosing studies | Not established | Not established | Community / vendor reported; widely repeated but original source could not be verified |
Amounts studied in human research
No established or reliably sourced dosing information was identified for thymulin as an administered human therapeutic. The human literature on thymulin is dominated by measurement of endogenous serum thymulin activity (a biomarker), not by dose-ranging administration trials of exogenous thymulin.
Amounts studied in animal research
Animal studies of thymulin and zinc-thymulin have used a range of injected doses in immune and neuroinflammatory models, but a single representative, consistently reported dose figure could not be confidently traced to a primary source for this entry. Readers researching a specific study should consult the primary paper directly rather than a secondary dosage summary.
Practitioner and community-reported protocols
Thymulin is offered by some research-peptide vendors and discussed in peptide-community forums with informally suggested subcutaneous protocols. These figures are widely repeated online, but their original source could not be verified, and they do not derive from published human dosing studies (community/vendor reported).
What circulates E5
Thymulin is offered by some research-peptide vendors and discussed in peptide-community forums with informally suggested subcutaneous protocols. These figures are widely repeated online, but their original source could not be verified, and they do not derive from any published human dosing study.
No specific amount, frequency, or duration was consistent enough across the sources reviewed for this entry to responsibly present as a single reported figure.
Recorded as an observation about what is published elsewhere. No figure here is a dose, a protocol, or a recommendation, and nothing in this section is evidence that any amount is safe or effective.
Side effects, risks, and limitations
Because thymulin has not been developed as an administered pharmaceutical with completed human trials, there is no well-characterized human side-effect profile for exogenous thymulin administration. As with other unregulated research peptides, material sold as “thymulin” carries risks of mislabeling, incorrect concentration, and contamination, since it is not manufactured or tested under pharmaceutical regulatory oversight. Its zinc dependency also means that interpreting or attempting to influence “thymulin levels” outside a clinical/laboratory context is not straightforward and should not be equated with simply taking a zinc supplement or the peptide itself.
Regulatory and developmental status
Thymulin is not an approved drug and is not marketed as a pharmaceutical product in the United States or, based on the sources reviewed, in other major regulatory jurisdictions. It exists primarily as a research reagent and a subject of endogenous-hormone research rather than as a developed drug candidate. Status verified as of the date below based on the absence of any identified regulatory approval or active late-stage development program in the literature reviewed.
Frequently asked questions
What is thymulin?
It is a naturally occurring nine-amino-acid, zinc-dependent thymic hormone (pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn) involved in T-cell development and immune regulation, first described in 1977.
Is thymulin the same as Thymalin?
No. Thymulin (FTS) is a specific, defined nonapeptide from international immunology research. “Thymalin” is a differently-sourced peptide product associated with Russian thymic-extract bioregulator research (linked to Vladimir Khavinson’s work). The two have different chemical identities and, based on the sources reviewed, different reported CAS numbers (thymulin is commonly listed as CAS 63958-90-7; Thymalin is reported by some vendor sources under a different CAS, such as 79621-14-0). Because these numbers come from different types of sources with different reliability, and because naming confusion between the two compounds is common online, readers should regard any single-source CAS claim for either substance with caution and verify against an authoritative chemical registry before relying on it.
What dosage has been studied in humans?
No established or reliably sourced human dosing information for administered thymulin was identified; human research has focused on measuring natural serum thymulin activity rather than dosing an administered peptide.
Does thymulin require zinc to work?
Yes. Thymulin is biologically inactive without a bound zinc ion; the active form is often specifically referred to as zinc-thymulin or Zn-FTS.
Has thymulin been studied in clinical trials?
Not as an administered therapeutic in the way a drug candidate typically is. Most human data involves observational measurement of endogenous thymulin activity in relation to age, zinc status, or disease states.
Is thymulin approved as a drug?
No. It is not an approved pharmaceutical product in the jurisdictions reviewed for this entry.
What remains unknown?
Whether administering exogenous thymulin (as opposed to correcting zinc status) produces meaningful clinical benefit in humans has not been established, and the precise relationship between the “Thymulin” and “Thymalin” naming confusion and any shared or separate CAS registry history has not been fully resolved from the sources available for this review.
Bottom line
Thymulin is a real, well-described zinc-dependent thymic nonapeptide with a solid foundation in basic immunology research, but it has not been developed into an approved human drug, and there is no established human dosing regimen for it as an administered therapeutic. It is frequently and incorrectly conflated online with “Thymalin,” a separate Russian thymic bioregulator product; the two should not be treated as interchangeable, and any CAS number or dosing claim for either one should be checked against its own, correctly attributed source.