Back to Registry

Thymosin Alpha-1

Also known as: Thymalfasin, Zadaxin, Tα1

Research Only

Molecular Formula

C129 H215 N33 O55 Fr Ba

Molecular Weight

3,108.31 Da (Free Base; Acetate salt variable)

Half-Life

~2 hours (serum half-life after subcutaneous administration in healthy volunteers)

Sequence

Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn-OH

Clinical Applications & Evidence

Mechanism of Action

Thymalfasin modulates innate and adaptive immune responses, in part via Toll-like receptor signaling (including TLR9) on dendritic and immune cells. Downstream signaling through MyD88, NF-κB, and IRF3 pathways influences T-lymphocyte maturation, Th1 cytokine secretion, and natural killer (NK) cell activity. Complete molecular mechanisms and direct receptor binding kinetics remain under investigation.

Investigated Uses

  • Foreign vaccine adjuvant authorization (Approved in Italy for influenza vaccination in immunocompromised adults; unapproved by US FDA)
  • Sepsis & critical care (2025 Phase 3 TESTS trial of 1,106 adults showed no 28-day mortality benefit: 23.4% Tα1 vs 24.1% placebo, P=0.93)
  • Chronic viral hepatitis B & C (Historical trials with mixed efficacy; largely superseded by modern direct-acting oral antivirals)
  • Adjunct oncology immunotherapy (Investigated in melanoma, NSCLC, and HCC; inconsistent clinical trial outcomes)
  • Immune reconstitution (Exploratory clinical studies in immunocompromised hosts; unproven for ME/CFS or fatigue)
Moderate Clinical Data

Regulatory & Safety Status

FDA Status

Research Only

WADA / Athletic Status

Not Explicitly Prohibited

Known Side Effects

Injection site reactions (redness, local discomfort, burning, or pain)Transient ALT flares observed during treatment of chronic hepatitis BTSH abnormalities and thyroid dysfunction reported in hepatitis C studiesFDA safety assessment notes potential immunogenicity, aggregation, and bioburden risks for compounded injectables

Contraindications

  • Hypersensitivity to thymalfasin or formulation excipients (Foreign label contraindication)
  • Pregnancy, lactation, and pediatric populations (Unstudied safety profile; foreign label restriction)
  • Hematopoietic stem-cell transplantation (Precautionary exclusion due to potential graft-versus-host disease or engraftment failure risks)
  • Autoimmune diseases (Requires individual clinical risk-benefit evaluation per foreign labeling)

Drug Interactions

  • Systemic immunosuppressants and corticosteroids (Theoretical blunting of immunomodulatory activity; foreign labels advise caution)

Citations & Clinical Trials

PubMed TESTS Phase 3 Trial: Thymosin Alpha 1 in Adults with Sepsis (2025) FDA FDA Briefing Document: Thymosin Alpha-1 — PCAC Meeting (December 2024) PubMed Thymosin α1 and Its Role in Viral Infectious Diseases (Molecules 2023) AIFA Italian AIFA Prescribing Information: Zadaxin (Thymalfasin) World Anti-Doping Agency WADA 2026 Prohibited List — S2 Category Guidance