Thymosin Alpha-1

Thymosin Alpha-1 has a genuine international trial and approval history, but it's not FDA-approved for any use in the United States. This page describes its mechanism and real research history — not dosing or usage guidance, and not a recommendation to use it. Talk to a doctor before considering it.

Thymosin Alpha-1 is a naturally occurring peptide fragment of prothymosin alpha, originally isolated from the thymus gland. It's an immunomodulator — its proposed mechanism involves recalibrating T-cell maturation and Th1/Th2 immune balance through TLR9 signaling on dendritic cells, which is why it's studied as an adjunct in infections, cancer immunotherapy, and immunodeficiency rather than as a performance or body-composition compound.

This is a substance with genuine clinical trial history — marketed internationally as Zadaxin, it has been evaluated in an estimated 4,400+ patients across 80+ clinical trials spanning chronic hepatitis B, chronic hepatitis C (combined with interferon), HIV adjunct therapy, cancer immunotherapy, sepsis, vaccine response enhancement, and primary immunodeficiency disorders. The US National Cancer Institute ran Phase I/II trials on it decades ago as part of its Biological Response Modifier program. That trial history is real and substantial, but it is specific to hepatitis, oncology-adjunct, and immune-deficiency contexts — not to fitness, anti-aging, or general wellness use, which have no comparable trial support.

Thymosin Alpha-1 is approved as Zadaxin in more than 35 countries — including China, Italy, and a range of countries across Asia, the Middle East, and Latin America — for hepatitis and immune-modulation indications. It has never been FDA-approved in the United States for any use. Its US compounding-pharmacy status is unsettled and separate from the BPC-157/TB-500 Category 2 removals: its bulk-substance nomination was withdrawn in September 2024 and referred to the FDA's Pharmacy Compounding Advisory Committee, which then voted against recommending it for the compounding-permitted list at meetings in late 2024. In February 2026, HHS Secretary Robert F. Kennedy Jr. publicly announced intent to have thymosin alpha-1 reconsidered under a broader peptide review, but as of this writing no formal FDA rulemaking reflecting that has been published. In short: real international approval history, no FDA approval, and a US compounding pathway that has already been reviewed once and rejected.