Thymosin α-1 (also known as Thymalfasin or Tα1) is a therapeutically researched peptide studied for its effects on anti-inflammatory, anti-aging, injectable. Thymosin α-1 (thymalfasin) is a 28-amino-acid immune-modulating peptide, approved abroad as Zadaxin for hepatitis B. Permitted under WADA rules.
Thymosin α-1 (international nonproprietary name thymalfasin) is a 28-amino-acid immune-modulating peptide cleaved from prothymosin alpha, the precursor protein encoded by the human PTMA gene. It acts on dendritic cells and T-cell maturation through Toll-like receptor signalling, sharpening the adaptive immune response rather than driving tissue growth. Marketed as Zadaxin, it is an approved prescription medicine in roughly 30 countries, including China and Italy, for chronic hepatitis B and as a vaccine adjuvant in immunocompromised patients; it has never been approved by the FDA in the United States, where it holds only orphan-drug designation.
Overview
It is one of the few compounds in this encyclopedia with genuine late-stage clinical evidence rather than rodent data alone.
Thymosin α-1 is permitted under World Anti-Doping Agency (WADA) rules.
That sets it apart from thymosin β-4 (TB-500), a tissue growth factor that WADA restricts under class S2.
Mechanism of action
Sharpens adaptive immunity by driving T-cell maturation and dendritic cell activity. Approved abroad as Zadaxin for chronic hepatitis B and as a vaccine adjuvant. Subcutaneous injection.
Reported effects
Effects reported in the literature and from preclinical models include:
- Stimulates T-cell differentiation and enhances thymic output, helping restore immune function lost to age-related thymic involution [2] Preclinical
- Improves vaccine response in the elderly and mitigates immunosenescence [2] Preclinical
- Exhibits anti-inflammatory and antioxidant activity while modulating dendritic cell and macrophage function [2] Preclinical
- Modulates immune signaling and inflammatory regulation relevant to autoimmune conditions such as Hashimoto's thyroiditis [1] Preclinical
Evidence grades: FDA approved Phase III Phase II Phase I Preclinical Anecdotal
Dosage and administration
Subcutaneous
- Chronic hepatitis B (approved regimen outside the US): 1.6mg twice weekly
Natty status
Thymosin α-1 is generally regarded as compatible with the natty designation, particularly when used for therapeutic healing purposes. Opinions vary across natural bodybuilding federations, and athletes who compete should consult the rulebook of their respective sanctioning body.[3]
Research
The peptide has been the subject of 3 studies and reference works collected on this site. The full bibliography is in § External links below.
Related compounds
Other peptides in this catalogue with overlapping mechanisms or status:
References
- ^ Peptide Therapies in Thyroid Health: Emerging Applications in Endocrine and Immune Modulation. Recent review
- a b c Aging and Thymosin Alpha-1. Recent review
- a b World Anti-Doping Agency. (2026). Prohibited List 2026.
External links
This page was last updated on July 17, 2026, at 16:26 (UTC).
Research last reviewed on July 17, 2026.
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