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Peptides, proteins & enzymes

Thymulin

Thymulin (serum thymic factor)

Thymulin is a defined zinc-dependent thymic peptide, also called serum thymic factor. Healthy-user memory or focus benefits and an oral nootropic dose are not established. Before comparing offers, distinguish purified thymulin from Thymalin thymus extract and Thymogen; similar names do not establish the same active ingredient.

Endogenous CompoundBioavailability SensitiveClinical ResearchMostly Animal EvidenceInsufficient EvidenceForm Dependent EvidenceLong Term Safety Unknown
Updated October 2026/6 min read/13 citations
Reviewed by the NootropicsIndex editorial team.Method: prioritize cited human research and official safety or regulatory sources; compare retailer-listed prices without endorsing products.Affiliate disclosure
01

What is it?

Thymulin and serum thymic factor

3

Thymulin is a nine-amino-acid hormone produced by thymic epithelial cells. Zinc binding is required for its biological activity. A peptide’s sequence alone therefore does not establish the zinc-bound active preparation studied in thymulin research.

Thymalin extract is a separate product identity7
Manufacturer-labelled Thymalin contains thymus extract, a mixture of peptides, rather than a declared amount of purified zinc-bound thymulin. Thymogen is another distinct peptide. A retailer using these names together does not demonstrate interchangeable ingredients, doses or routes.
02

Names, aliases and forms

Common NameSerum thymic factor
AcronymFTS
Regional NameFacteur thymique serique
03

Mechanisms of action

What the human biomarker studies show

4

In a small human zinc-deficiency study, zinc supplementation restored reduced activity of endogenous thymulin. Participants received zinc, not thymulin; the finding is not evidence for memory enhancement from thymulin products or for adding zinc to a peptide regimen.

04

Potential effects and evidence map

Human zinc studies measured the body’s own thymulin rather than giving thymulin. Historical trials administered synthetic nonathymulin to patient groups, with mixed clinical findings. Animal, cell and gene-transfer research does not establish cognitive benefit in healthy supplement users.

Effect domainMagnitudeGrade
Memory / learning5
UnknownConfidence: Low

A memory or learning benefit in healthy adults is not established by the available thymulin research.

Note No healthy-adult cognitive effect size is available; this rating denotes unestablished benefit rather than a measured zero-effect trial.

0/5
E
05

Typical dosages and timing

Synthetic nonathymulin in patients91-10 mg/day

No oral nootropic regimen is established for healthy adults. Historical nonathymulin trials in rheumatoid-arthritis patients compared 1, 5 and 10 mg/day of a synthetic thymic peptide. Those patient-specific study amounts are not a consumer dose and cannot be derived from Thymalin extract vial mass or Thymogen spray concentration.

06

Timing & effect horizon

Effect horizonUnknown
Unknown
Human duration and cycling remain uncertain11

The sources reviewed do not establish human cognitive onset, benefit duration, The time for blood levels to fall by half during the final elimination phase.Source or a validated cycle. A reported rapid blood-clearance measurement came from one injected sheep. That animal result cannot set a human dosing interval, and the length of a patient study is not the duration of an effect.

07

Safety, side effects and risk profile

Evidence uncertainty10
Confidence: High

The evidence does not support a numerical risk estimate for healthy-adult supplement use.

Note Small historical patient studies of injected synthetic nonathymulin cannot establish oral, long-term, pregnancy, lactation or combination safety.

Unscored
E
Why the safety rating is unscored10

Safety is unknown for typical healthy-adult supplement use. A small six-month patient trial of injected synthetic nonathymulin reported no significant side effects, but it cannot determine the safety of oral or retail peptide products, uncommon harms, long-term exposure, pregnancy or breastfeeding. Unknown is an evidence gap, not a low-risk finding.

Quality hazards are separate from intrinsic peptide risk13

Injection products require quality controls beyond a sequence or purity claim. FDA guidance on compounded drugs identifies contamination and incorrect active content as causes of serious harm. This is a route and manufacturing concern, not a measured thymulin-specific adverse-event rate; a research label or certificate alone does not establish suitability for human use.

08

Interactions and cautions

Interaction data do not establish safe stacks5

The reviewed thymulin physiology literature describes immune and endocrine signalling, largely in experimental settings. It does not establish safe combinations with immune-active medicines, hormones, zinc supplements or other peptides. Biological plausibility should not be presented as a proven clinical interaction or a co-dosing protocol.

09

Legal and regulatory status

United States: product category matters12

As of October 2026, FDA describes US dietary supplements as ingested products and does not preapprove them for safety and effectiveness. A peptide vial intended for injection should not be assumed to have dietary-supplement status. Classification and lawful sale depend on the exact product, route and claims; this US framework does not determine authorisation or import rules in other countries.

10

How it compares

Thymogen is not a thymulin formulation8

Thymogen’s official leaflet identifies alpha-glutamyl-tryptophan as its active ingredient. It is a separate peptide, not a nasal, topical or injectable version of the nine-amino-acid thymulin molecule. Compare it under its own ingredient identity.

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Practical buying and quality notes

  • For a defined thymulin preparation, compare documented peptide identity, zinc-bound form, amount and intended route. For Thymalin, the labelled amount refers to thymus extract. A milligram of that mixture is not a verified milligram of thymulin, so the two cannot share a meaningful price-per-milligram ranking.7
12

FAQ

What is a supported thymulin dosage?

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Healthy-user dosage evidence does not establish a validated amount or oral regimen. Manufacturer directions for a similarly named extract and retail vial sizes cannot fill that gap. The dosage section explains the limited historical patient-study context.

How long does thymulin last, and should it be cycled?

10

No reliable human benefit-duration or cycling protocol was identified. The historical multiple-sclerosis trial observed patients for six months of injections and six months afterward; it found no significant difference from placebo on its clinical scales. Those observation windows are not an effect-duration claim or a recommended cycle.

13

References

  1. PubChem. Thymulin, CID 71300623. Accessed 19 October 2026.
  2. Bach JF, Dardenne M. Thymulin, a zinc-dependent hormone. Med Oncol Tumor Pharmacother. 1989;6(1):25-29.
  3. Dardenne M, Savino W, Berrih S, Bach JF. A zinc-dependent epitope on the molecule of thymulin, a thymic hormone. Proc Natl Acad Sci U S A. 1985;82(20):7035-7038.
  4. Prasad AS, et al. Serum thymulin in human zinc deficiency. J Clin Invest. 1988;82(4):1202-1210.
  5. Reggiani PC, et al. Physiology and therapeutic potential of the thymic peptide thymulin. Curr Pharm Des. 2014;20(29):4690-4696.
  6. The Influence of KE and EW Dipeptides in the Composition of the Thymalin Drug on Gene Expression and Protein Synthesis Involved in the Pathogenesis of COVID-19. Int J Mol Sci. 2023;24(17):13377.
  7. Samson-Med. Thymalin: active substance and product information. Accessed 19 October 2026.
  8. Cytomed. Thymogen intramuscular solution: patient information leaflet. Accessed 19 October 2026.
  9. Amor B, Dougados M, Mery C, Dardenne M, Bach JF. Nonathymulin in rheumatoid arthritis: two double blind, placebo controlled trials. Ann Rheum Dis. 1987;46(7):549-554.
  10. Roullet E, et al. Nonathymulin treatment of multiple sclerosis: double-blind pilot study. Acta Neurol Scand. 1989;80(6):575-578.
  11. Davis SL, Safieh-Garabedian B, Khosraviani M. Concentrations of thymulin in unextracted serum from pigs, sheep and cattle as measured by ELISA. J Immunoassay. 1994;15(2):191-211.
  12. US Food and Drug Administration. FDA 101: Dietary Supplements. Accessed 19 October 2026.
  13. US Food and Drug Administration. Understanding the Risks of Compounded Drugs. Accessed 19 October 2026.
Note

This page is informational and summarizes available evidence. It is not medical advice, a recommendation, or a substitute for guidance from a qualified clinician.