Thymosin α1

also known as: Tα1, thymalfasin, Zadaxin, TA1

The most clinically studied thymic peptide — approved in 35+ countries as Zadaxin for hepatitis B and C, with 30+ RCTs across more than 11,000 subjects. Not FDA-approved despite extensive global use.

A 28-amino-acid N-acetylated peptide first isolated from thymic tissue by Allan Goldstein in 1977, identical to the N-terminal fragment of prothymosin alpha, approved in over 35 countries under the brand name Zadaxin for chronic hepatitis B and C and as an immune enhancer.

Mechanism of action

Modulates both innate and adaptive immunity. Activates TLR2 and TLR9 on dendritic cells and monocytes, driving NF-κB activation and production of IL-12, TNF-α, and IL-6. Promotes dendritic cell maturation, T-cell differentiation (particularly Th1), and enhances NK cell cytotoxicity. Restores immune function in immunocompromised states (hepatitis B/C, sepsis, post-chemotherapy) and enhances vaccine responses in elderly and hemodialysis populations.

Primary uses

Chronic hepatitis B and C (Zadaxin-approved)
Immune enhancement in immunocompromised patients
Sepsis (investigational)
Severe COVID-19 (investigational)
Vaccine adjuvant research
Community off-label immune support

Typical dosing

1.6 mg twice weekly (subcutaneous)

Standard Zadaxin dose: 1.6 mg (900 µg/m²) subcutaneously twice weekly for 6–12 months. Community dosing often mirrors this.

Regulatory status

Approved in 35+ countries (including Italy, China, and much of Asia) as Zadaxin / thymalfasin for chronic hepatitis B, chronic hepatitis C, and as an immune enhancer. FDA orphan drug designations for malignant melanoma, chronic active hepatitis B, DiGeorge anomaly with immune defects, and hepatocellular carcinoma — but not FDA-approved for marketing. Manufactured by SciClone Pharmaceuticals.

References

[fda-pi] Zadaxin (thymalfasin) Prescribing Information. SciClone Pharmaceuticals. (Approved in 35+ countries; not FDA.)
[clinical-trial] Chien RN, et al. "Efficacy of thymosin alpha1 in patients with chronic hepatitis B: a randomized, controlled trial." Hepatology, 1998;27:1383-1387.
[review] Dominari A, et al. "Thymosin alpha 1: A comprehensive review of the literature." World J Virol, 2020;9:67-78.
[pubmed] Garaci E, et al. "Thymosin alpha 1 in the treatment of cancer: from basic research to clinical application." Int Immunopharmacol, 2003;3:1145-1150.

Related peptides

Thymulin

A zinc-dependent thymic peptide — biologically active only when zinc-saturated, making serum thymulin activity a functional readout of zinc status.

Thymopentin

A synthetic pentapeptide fragment of thymopoietin — historically marketed as Timunox for immunodeficiency, now primarily used in research and limited European clinical practice.

Thymosin β4

The natural 44-amino-acid parent of the TB-500 research peptide — in clinical trials (as RGN-259/Lacripep) for dry eye disease, corneal wounds, and dermal healing.

Disclaimer

This entry is for educational purposes only and does not constitute medical advice. Dosing information reflects published regulatory or research data and is not a recommendation. Many compounds described here are not approved for human use in the United States. Consult a licensed medical professional before considering any peptide therapy.