For Research Use Only – Not for Human Consumption. For Research Use Only. Not for Human Consumption. Not for diagnostic, therapeutic or medical use. Statements have not been evaluated by the FDA.
Thymosin Alpha-1: Real Human Trials, Mixed Results
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Key points
- An acetylated 28-amino-acid peptide originally linked to the thymus gland.
- Human trials exist in hepatitis and sepsis; the 2025 TESTS sepsis trial (1,089 patients) found no mortality difference versus placebo.
- Not FDA-approved in the U.S., though approved as thymalfasin (Zadaxin) in many other countries.
What it is
Thymosin alpha-1, also called thymalfasin, is a 28-amino-acid peptide with an acetyl cap on one end, weighing roughly 3,108 daltons. It was first associated with extracts from the thymus.
How researchers study it
Research covers T-cell and innate-immune signaling, cytokine patterns, and host-response models.
What the evidence shows
Unlike many peptides, it has been tested in people, notably in hepatitis and sepsis, and the results are mixed. The large 2025 TESTS sepsis trial, with 1,089 participants, found no difference in mortality compared with placebo. Nothing in the evidence supports a general wellness or longevity use.
Regulatory status
It is not FDA-approved in the United States. In a number of other countries it is approved under the name thymalfasin, sold as Zadaxin.
