Thymulin

What is thymulin?

Thymulin is a nine-amino-acid thymic peptide with sequence pyroglutamyl-alanyl-lysyl-seryl-glutaminyl-glycyl-glycyl-seryl-asparagine. It was historically called serum thymic factor or facteur thymique sérique. Nonathymulin is the INN for the defined synthetic peptide used in historical drug research.

The classic biochemical distinction is between FTS (zinc-free nonapeptide, little or no recognized activity in the traditional bioassay) and FTS-Zn (active form when peptide binds zinc in ~1:1 molar relationship). Zinc dependence is not marketing detail — it creates a biologically recognized epitope. ([PNAS zinc-epitope study](https://pmc.ncbi.nlm.nih.gov/articles/PMC391304/))

NIH/NCATS lists free-peptide formula C33H54N12O15, mass 858.8533 Da, CAS 63958-90-7, UNII 9H198D04WL. Thymulin acetate has higher gross mass (~918.91 Da commercial certificate) — do not interchange when calculating active peptide. ([Inxight Drugs](https://drugs.ncats.io/drug/9H198D04WL))

Identity and naming checks

The most common online error is importing a 20-day thymalin regimen into a thymulin page. Thymalin ≠ thymulin. Also distinct: thymosin alpha-1, TB-500/Tβ4, thymopentin, thymopoietin, PAT analogue, and homeopathic 5CH preparations.

Before any laboratory administration, establish intact mass, sequence (including N-terminal pyroglutamate), quantitative peptide assay, counterion/water content, zinc molar ratio, bioactivity assay, sterility/endotoxin, and stability-indicating methods. An HPLC purity percentage cannot answer most of these questions.

Product, zinc, salt, and assay checks

Current animal work used thymulin acetate plus equimolar ZnCl2. “Equimolar” means one mole of zinc reagent for each mole of peptide — not equal mass. For 1 mg free peptide: ~0.001164 mmol → ~0.159 mg anhydrous ZnCl2. That example is laboratory stoichiometry, not a self-mixing instruction.

U.S. and international status

There is no U.S. prescribing label or FDA-established dosage for thymulin. The [FDA UNII record](https://precision.fda.gov/uniisearch/srs/unii/9H198D04WL) identifies the substance but notes UNII does not imply regulatory review or approval.

The [NIH/NCATS drug record](https://drugs.ncats.io/drug/9H198D04WL) describes nonathymulin as investigational and states historical development for ischemic heart disorders and rheumatoid arthritis was discontinued. No currently approved finished thymulin/nonathymulin medicine with verified national prescribing dose was identified in major accessible registries.

Historical clinical development and publication do not equal a current national label. Absence of verified current approval is not proof no historical authorization ever existed — but there is no defensible universal dose.

Dosage used in human clinical research

The table reports administered exposures from primary human literature. A historical dose is not a recommendation, and missing route, formulation, or duration should remain missing rather than filled with assumptions.

Rheumatoid arthritis: 1, 5, and 10 mg/day

The best-known human dose comparison is a 1987 report of two randomized, double-blind, placebo-controlled RA trials. Participants received nonathymulin at 1, 5, or 10 mg/day. 5 mg/day was most effective: 56% globally improved vs 17% placebo (p < 0.02). The response did not track with clear immunological changes. ([Amor et al., 1987](https://pubmed.ncbi.nlm.nih.gov/3310925/))

Limitations: nearly four decades old; abstract omits route, zinc formulation, exact duration; non-monotonic dose-response (5 mg > 1 or 10 mg); did not establish benefit for healthy aging, infection, or nonspecific immune support. Withdrawals in the 5 mg group after thrombocytopenia (month 3) and vasculitis (month 5) deserve mention — causality not established.

Single 500 mcg subcutaneous exposure

A 1984 RA experiment administered 500 mcg synthetic zinc-supplemented FTS SC once to five participants. Lymphocyte subsets measured before and one hour later. Same report exposed cells in vitro to 0.125, 1.25, and 12.5 ng/mL — in vitro concentrations are not injectable doses. ([Faure et al., 1984](https://doi.org/10.1016/0192-0561(84)90058-4))

Clearest primary evidence for a documented SC human amount — but n=5 and one-hour window cannot establish a clinical protocol.

Multiple sclerosis: six months SC with no clear benefit

A randomized study of 40 matched MS participants received nonathymulin or placebo SC for six months plus six months observation. No significant difference in Kurtzke disability, Ambulation Index, or Functional Scale outcomes; no significant side effects. Exact dose absent from abstract — must not be inferred from RA program. ([Haahr et al., 1989](https://pubmed.ncbi.nlm.nih.gov/2618585/))

Topical zinc-thymulin pilot

An uncontrolled androgenetic-alopecia pilot used 0.0005% zinc-thymulin, 1–2 mL twice daily for 4–10 months. Arithmetic reconstruction: 0.0005% w/v = 5 mcg/mL → 5–10 mcg per application → 10–20 mcg/day on scalp. Study-specific zinc oxide preparation — not interchangeable with injectable acetate. ([Topical pilot](https://doi.org/10.4172/2167-0951.1000147))

Eighteen enrolled; 11 used ≥6 months. Visual analogue score improved (p = 0.045) but no placebo, blinding, or validated hair-count endpoint.

Human cells exposed outside the body

The 2026 Nature Communications study exposed human PBMCs to 1 mcg/mL thymulin plus equimolar ZnCl2 for 24 hours before inflammatory stimulation. This was ex vivo — not a blood target, infusion concentration, or human dose. Untreated human blood/tumor datasets were analyzed without systemic thymulin administration. ([Kanemaru et al., 2026](https://www.nature.com/articles/s41467-026-75383-0))

Reported human research dosage range

There is no scientifically defensible “standard thymulin dose” selectable from this table. The human record is too old, sparse, and formulation-incomplete.

Thymulin community protocols

There is no stable community consensus on amount, frequency, zinc formulation, duration, or purpose. Schedules without zinc-state specification are not reproducible.

Clinical research versus community reports

Complete evidence-anchored research dosing protocol

Replication of thymulin's effect on tumor progression and age-associated myeloid inflammation in aged mice — a nonclinical protocol. Current primary literature provides defined molecule, zinc condition, route, dose, tumor model, duration, and endpoints in mice. It does not convert animal exposure into a human dose. Requires IACUC approval, veterinary oversight, and trained personnel.

Animal and preclinical thymulin doses

Animal / preclinical research only. These doses are not human protocols. Do not convert to human-equivalent doses — zinc complexation, species biology, route change, and product bioactivity are unresolved.

Reconstitution and U-100 syringe math

Tables show concentration and volume arithmetic for a vial whose active-peptide content and final volume are known. They do not establish sterility, zinc-complexed state, stability, or suitability for human use.

Concentration (mg/mL) = vial peptide (mg) ÷ final volume (mL) · Volume (mL) = desired amount (mg) ÷ concentration · U-100 units = volume (mL) × 100.

Cross-check whether labeled mass is free-peptide equivalent, acetate gross mass, assay-corrected peptide, or nominal fill. 10 mg/mL is arithmetic, not evidence the peptide-zinc complex remains soluble, stable, or tolerable. Treating gross salt mass as active-peptide mass is a common error.

Administration routes in the literature

Storage and handling

Record reconstitution date, final volume, concentration, zinc condition, lot, and appearance. Do not assume bacteriostatic water creates a 28-day stability period.

What can research reasonably measure?

Common dosing claims vs evidence

Dosage evidence ladder

Overall thymulin dosing evidence: low. Human administration is real but old, small, and incompletely reported. The 5 mg/day RA signal is the strongest dose-comparison result, not a universal dose. Modern community protocols sit below human and animal literature because they lack matched controlled studies and often omit zinc state.

Safety and tolerability

Human safety database is small and old. RA trials described adverse effects as minimal overall, but thrombocytopenia and vasculitis withdrawals in the 5 mg group deserve attention. MS abstract reported no significant side-effect difference. Topical pilot: one transient redness episode.

Plausible research risks include immune modulation in autoimmune/infection/malignancy contexts, uncontrolled zinc exposure, hypersensitivity, injection-related harms, contamination/endotoxin, hematologic changes, and unknown reproductive/cancer effects in humans.

Drug and treatment interactions

Anti-doping status

Thymulin is not specifically named on the 2026 WADA Prohibited List. However, section S0 Non-Approved Substances covers pharmacological substances without current approval by a governmental regulatory health authority for human therapeutic use. Because no current approved thymulin medicine was verified, thymulin could fall within S0 and be prohibited at all times. ([2026 WADA Prohibited List](https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf))

Bottom line

Thymulin has a genuine but limited human research history. The most informative dose comparison used 1, 5, and 10 mg/day in RA with the strongest signal at 5 mg/day. A separate experiment used 500 mcg SC once; an MS trial found no significant benefit; a topical pilot used 0.0005% zinc-thymulin twice daily. None establishes a modern universal regimen.

The most reproducible current dosing evidence is nonclinical: 1.5 mg/kg IP once daily with equimolar ZnCl2 in aged mice. Any thymulin research must define peptide identity, active-content basis, zinc stoichiometry, sterility, and route. ≠ thymalin. Community schedules remain inconsistent and frequently conflate thymulin with thymalin or thymosin alpha-1.

FTS (zinc-free) ≠ FTS-Zn (active). 5 mg/day RA signal ≠ universal dose. 1.5 mg/kg mouse IP × 28 d — animal only, no HED. Thymalin 20-day cycles ≠ thymulin evidence.

Frequently asked questions

References

• NIH/NCATS

  Inxight Drugs: Nonathymulin

  Investigational status; molecular identity.

• Amor et al.

  Nonathymulin in rheumatoid arthritis: two double-blind trials

  Ann Rheum Dis. 1987 — 1, 5, 10 mg/day.

• Faure et al.

  Thymulin modulation of T-cell subsets — 500 mcg SC experiment

  Clin Immunol Immunopathol. 1984.

• Haahr et al.

  Randomized nonathymulin trial in multiple sclerosis

  Acta Neurol Scand. 1989.

• Kanemaru et al.

  Thymulin restrains age-associated myeloid inflammation and enhances cancer immunotherapy

  Nat Commun. 2026 — 1.5 mg/kg IP mouse protocol.

• PNAS

  A zinc-dependent epitope on the molecule of thymulin

  Zinc epitope structural work.

• World Anti-Doping Agency

  2026 Prohibited List

  S0 Non-Approved Substances.