Thymosin Alpha-1
Immune Modulating Peptideapproved_internationalAlso known as: Tα1, Ta1, Thymalfasin, Zadaxin
A 28-amino acid thymic peptide that modulates immune function, approved in multiple countries for hepatitis B and used as an immune enhancer in cancer and infectious disease.
Overview
Thymosin Alpha-1 (Tα1) is a naturally occurring 28-amino acid peptide originally isolated from thymosin fraction 5 of the thymus gland. It plays a critical role in immune system maturation and regulation, particularly in T-cell development and function. The synthetic version, thymalfasin (marketed as Zadaxin), is approved in over 35 countries for treatment of hepatitis B and as an immune adjuvant. Tα1 acts as an immune modulator rather than a simple stimulant — it enhances immune responses when they are suppressed and can also temper excessive inflammation. This dual action makes it valuable for immunocompromised patients, chronic viral infections, cancer immunotherapy adjunctive treatment, and potentially for immune aging (immunosenescence). During the COVID-19 pandemic, Tα1 received significant attention for its potential to improve outcomes in severe infections.
Mechanism of Action
Thymosin Alpha-1 modulates immunity through multiple pathways: (1) Activates dendritic cells via TLR2, TLR7, and TLR9, enhancing antigen presentation; (2) Promotes T-cell maturation and differentiation, particularly CD4+ and CD8+ T cells; (3) Enhances NK cell cytotoxicity; (4) Stimulates IL-2 and IFN-alpha production for antiviral defense; (5) Modulates inflammatory cytokines, reducing excessive IL-6 and TNF-alpha while boosting protective immune responses; (6) Restores immune function in immunosenescent or immunocompromised states; (7) May enhance vaccine efficacy by improving adaptive immune responses.
Molecular Formula
C129H215N33O55
Molecular Weight
3108.3 g/mol
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
Dosage Protocols
Dose Range
1.6mg – 3.2mg
Frequency
2-3 times per week
Route
subcutaneous
Cycle Length
4-12 weeks, cycled
Standard dose is 1.6mg (based on Zadaxin clinical dosing). Administered subcutaneously, typically in the abdomen. Can be cycled for ongoing immune support.
Source: Zadaxin prescribing information and clinical protocols
Side Effects
| Effect | Severity |
|---|---|
| Injection site reaction | mild |
| Fatigue | mild |
| Muscle aches | mild |
| Low-grade fever | mild |
Pros & Cons
Approved pharmaceutical product in 35+ countries with extensive clinical use history
Acts as an immune modulator, not just stimulant — balances both underactive and overactive immune states
Remarkably safe profile with minimal side effects across decades of clinical use
Broad therapeutic potential: viral infections, cancer immunotherapy, vaccine enhancement, and immunosenescence
Well-characterized mechanism of action with clear immune biomarker effects
Not FDA-approved in the US, limiting access to compounding pharmacies or research suppliers
Requires injection administration (no oral formulation available)
May be inappropriate for patients with autoimmune conditions due to immune-enhancing effects
Relatively expensive compared to other immune-support peptides
Research Studies
Legal Status
Approved in 35+ countries (Zadaxin) for hepatitis B and as an immune adjuvant. Not FDA-approved in the US but available as a compounded or research peptide. Orphan drug designation in the US for certain indications.
Related Peptides
Semaglutide
An FDA-approved GLP-1 receptor agonist used for type 2 diabetes and chronic weight management, producing significant weight loss of 15-17% body weight in clinical trials.
BPC-157
A 15-amino acid synthetic peptide derived from human gastric juice that promotes healing of tendons, ligaments, muscles, gut lining, and other tissues through multiple regenerative pathways.
Tirzepatide
A first-in-class dual GIP/GLP-1 receptor agonist that produces up to 22.5% body weight loss, approved for type 2 diabetes and obesity management.
Ipamorelin
A highly selective growth hormone-releasing peptide (GHRP) that stimulates GH release with minimal impact on cortisol, prolactin, or appetite, making it the cleanest GHRP available.