Thymosin Alpha-1

Thymic peptide / immune modulator · Also known as Zadaxin, Thymalfasin

What is thymosin alpha-1?

A 28-amino-acid peptide naturally produced by the thymus gland that plays a central role in immune system regulation. Its synthetic form, thymalfasin, has been approved in over 35 countries for conditions including hepatitis B, hepatitis C, and as a vaccine adjuvant.

Thymosin Alpha-1 was first isolated from thymic tissue in the 1970s and its synthetic version (thymalfasin, marketed as Zadaxin) has become one of the most clinically studied immune-modulating peptides, with data from over 11,000 human subjects across more than 30 clinical trials. It has received orphan drug designation from the FDA for hepatocellular carcinoma and malignant melanoma, and is approved in over 35 countries for hepatitis B and C treatment, vaccine enhancement, and immune deficiency conditions.

Key takeaway: Thymosin Alpha-1 is one of the most extensively studied immune peptides, approved in over 35 countries with clinical data spanning thousands of patients and decades of use.

Benefits & evidence

Immune system modulation High confidence
Hepatitis B/C treatment High confidence
Vaccine response enhancement High confidence
Cancer immunotherapy support Moderate confidence
Infection recovery Moderate confidence

How it works

Thymosin Alpha-1 acts as a master regulator of the immune system. It promotes the maturation of T cells in the thymus, specifically driving the development of CD4+ helper and CD8+ cytotoxic T cells. It also directly activates natural killer (NK) cells and enhances dendritic cell function, improving the body’s ability to detect and respond to pathogens and abnormal cells.

Beyond direct immune cell activation, Thymosin Alpha-1 modulates the balance between pro-inflammatory and anti-inflammatory responses. It increases production of key cytokines like interferon-alpha and interleukin-2 while helping prevent excessive inflammation. This dual role - boosting immune surveillance while maintaining balance - is why it has shown benefit across such a wide range of conditions, from chronic viral infections to cancer immunotherapy to vaccine enhancement.

Dosing information

Typical dosing protocol
Starting dose

1.6 mg twice weekly

Ongoing
Maintenance dose

1.6 mg twice weekly

6-12 months typical course

Administered as a subcutaneous injection. Approved in 35+ countries but carries only orphan drug designation in the US.

Side effects

Most side effects tend to improve as your body adjusts.

Injection site reaction Common
Transient fatigue Uncommon
Mild flu-like symptoms Uncommon
Fever Rare
Allergic reaction Rare

Research (10 studies)

Aging and Thymosin Alpha-1. International journal of molecular sciences · 2025