# Thymosin α-1

Thymosin α-1 (Tα1) is a 28-amino-acid peptide, cut from a precursor (prothymosin α), naturally made by the epithelial cells of your thymus. It tunes both innate and adaptive immunity, by activating TLR signaling in dendritic cells and monocytes and pushing Th1-type T-cell responses. Your thymus shrinks substantially from early adulthood. As its output falls, T cells age and immunity weakens, so Tα1 supplements are proposed to partly make up the deficit. A version called Thymalfasin (Zadaxin, SciClone) is approved in over 35 countries, but not the US, as an add-on for chronic hepatitis B and C and as an immune booster in people with weak immunity. It has been used off-label during COVID-19 outbreaks in several countries. But there is no human evidence for an anti-aging or longevity benefit. Trials in cancer and infection support its immune-modulating activity, though effect sizes vary. Anti-aging clinics market it widely, and its legal status ranges from approved drug to unregulated peptide depending on the country. In the US, the FDA's status has shifted: it added Tα1 to 'Category 2' of the interim 503A bulks list on 29 September 2023, removed it (after the nominator withdrew) effective 27 September 2024, and on 4 December 2024 the FDA's compounding advisory committee voted against putting it on the 503A allowed list. So it is not eligible for 503A compounding in the US.

## Sources

- Dominari A, Hathaway D III, Pandav K et al.. (2020). Thymosin alpha 1: A comprehensive review of the literature. World Journal of Virology. https://doi.org/10.5501/wjv.v9.i5.67
- Simonova MA, Ivanov I, Shoshina NS, Komyakova AM, Makarov DA, Baranovskii DS, Klabukov ID, Telepenina KP, Atiakshin DA, Shegay PV, Kaprin AD, Stepanenko VN. (2025). Aging and Thymosin Alpha-1. International Journal of Molecular Sciences. https://doi.org/10.3390/ijms262311470

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_Canonical: https://longevity-switzerland.com/en/glossary/thymosin-alpha-1 · Part of Longevity Cities · Updated 2026-06-22_