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Thymosin alpha-1 (thymalfasin, brand Zadaxin) is a 28-amino-acid immune-modulating peptide. It's approved in 35+ countries (for hepatitis B/C and as an immune adjuvant) but is not FDA-approved in the US.
How it works
It helps modulate the immune system — promoting T-cell differentiation and maturation and acting on innate immune signaling (it's described as a toll-like-receptor agonist). That's why it's studied as an immune adjuvant.
The evidence
It has an unusually large evidence base for this space — a 2024 review cited evidence from 30+ clinical trials and 11,000+ subjects, and it's been studied in hepatitis and sepsis. Strength of evidence varies by condition, so read specifics before generalizing.
Safety
Reported as generally well tolerated in its approved uses, with injection-site reactions among effects. Because it modulates immunity, use in autoimmune conditions or with immune-affecting drugs is a clinician conversation. The US status differs from the countries where it's approved.
FAQ
QIs it FDA-approved?
No — it's approved in many other countries (as Zadaxin) but not by the US FDA.
QWhat's it used for where approved?
Chiefly hepatitis B/C and as an immune adjuvant; it's been studied in other immune contexts too.
Sources
This profile summarizes the following. Follow the links to read the originals — and remember that summaries age, so check for newer information.
Inclusion here is not endorsement of any source's claims; several are cited so you can compare how different outlets characterize the same evidence.
Questions & comments
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