A thymic peptide that modulates T-cell immunity — approved in 35+ countries for hepatitis and cancer.
Thymosin Alpha-1 (Tα1) is a 28-amino acid peptide naturally produced by the thymus gland. It is the predominant biologically active thymosin — a family of peptides originally isolated from bovine thymus gland by Allan Goldstein in the 1960s. Tα1 plays a central role in T-cell development, differentiation, and function — it is essentially the master regulator of adaptive immunity.
The thymus, which produces Tα1, gradually atrophies (shrinks) with age — thymic involution. By the time most people reach their 40s-50s, thymic function has declined substantially. This correlates with declining T-cell mediated immunity that accompanies aging. Supplementing Tα1 is thought to partially restore some aspects of immune competence that decline with age.
SciClone Pharmaceuticals developed synthetic Tα1 as Zadaxin (thymalfasin), which is approved in 35+ countries for chronic hepatitis B, hepatitis C (in combination with interferon), and as an immune adjuvant for certain cancers and vaccines. Despite extensive global approval and decades of clinical data, Zadaxin has not received FDA approval.
Zadaxin has been studied in multiple large clinical trials. For hepatitis B, sustained HBeAg seroconversion rates improved with Tα1 treatment. In hepatitis C combined with interferon, response rates increased. In cancer (particularly hepatocellular carcinoma), Tα1 as adjuvant therapy showed improved survival in some studies.
Mechanistically, Tα1 promotes Th1 immune responses (cellular immunity), increases CD4+ and CD8+ T-cell counts, enhances NK cell activity, and increases interferon-gamma production. It has also been studied for vaccine adjuvancy and COVID-19 treatment. The COVID-19 pandemic generated renewed interest in Tα1 for critically ill patients.
📚 Key Reference: PMID: 1717440 (Thymosin Alpha-1 original), PMID: 26248541 (hepatitis B meta-analysis)
Excellent safety record from decades of global clinical use. Well-tolerated with minimal side effects. Injection site reactions are the most common complaint. No significant drug interactions documented. Rare reports of fever. Considered one of the safest immune-modulating peptides. Consult your provider for your specific indication.
NOT FDA-approved in the US despite 35+ country approval worldwide. Available through compounding pharmacies in the US. Zadaxin is the branded pharmaceutical form by SciClone Pharmaceuticals. The discrepancy between global approval and US non-approval is largely commercial/regulatory pathway related, not safety-based.