The Peptide Atlas
Thymosin Alpha-1
A 28-amino-acid peptide originally isolated from the thymus, the gland where immune T-cells learn their job.
Class
Thymic immune peptide
Evidence
Human-tested
Status
Approved in many countries (Zadaxin); not FDA-approved in the U.S.
Forms
Subcutaneous injection
What people use it for
Immune support: people recovering from long illness, dealing with frequent infections, or interested in the aging immune system.
The signal
The thymus shrinks dramatically with age, and T-cell training declines with it. Thymosin alpha-1 is one of the thymus's own signaling peptides, and giving it nudges T-cells toward maturing and responding.
How it works
It acts on immune-cell receptors that shape how T-cells mature and how strongly they respond, tilting a sluggish immune response toward engagement [1].
What the research shows
A genuinely large human record: it's been through randomized trials in chronic hepatitis B [2], severe infections [3], and as a vaccine booster in people who respond weakly, and it's an approved drug in dozens of countries under the name Zadaxin [1]. Results vary by condition, and the U.S. never saw the pivotal program the FDA would need.
What people get wrong
That "immune-boosting" means more is better. Its trial record is in specific conditions with impaired immunity. And people confuse it with thymosin beta-4 (TB-500), which is a repair peptide, not an immune one. Same gland in the name, different molecules.
References
- Int J Mol Sci (2025). Aging and Thymosin Alpha-1. PubMed
- BMC Gastroenterol (2020). The clinical efficacy and adverse effects of entecavir plus thymosin alpha-1 combination therapy in chronic hepatitis B. PubMed
- Front Immunol (2025). Thymosin alpha 1 alleviates inflammation and prevents infection in patients with severe acute illness. PubMed
Last reviewed 2026-08-24. Every reference is verified against the primary literature at review time. How the Atlas grades evidence