Thymosin Alpha-1
Thymalfasin (Thymosin α1; Tα1)
Not FDA-approved in the US. Not on the FDA Category 2 list (only the TB-4 fragment/TB-500 is listed). Approved internationally under the brand name Zadaxin in over 30 countries.
A natural immune-boosting peptide that strengthens the body's defenses by enhancing several types of immune cells, including those that detect threats, fight infections, and destroy abnormal cells. It is approved in over 35 countries for treating chronic hepatitis B and C, but is not approved by the US FDA.
This entry is a cited research summary, not an established treatment reference. Dosing language is included as source context, not as medical instruction.
Safety Summary
Thymosin Alpha-1 has an exceptionally well-documented safety profile across >11,000 patients in 30+ clinical trials. Phase I dose-escalation found no dose-limiting toxicities up to 9.6 mg/m² (highest tested dose; MTD not reached). In the TESTS Phase 3 trial (n=1106), serious adverse events were similar between Tα1 (26%) and placebo (29%). No black box warnings. Long-term use (6--12 months) in hepatitis trials showed consistent safety with no evidence of cancer promotion or organ toxicity. Community users report occasional 'Herxheimer-like' immune flare reactions, particularly in Lyme disease or autoimmune conditions -- recommending starting at lower doses (PMC7747025).
Clinical check-in
If real-world use or exposure is being considered, review potential interactions, contraindications, and monitoring needs with a licensed clinician rather than relying on summary copy alone.
Sources: [1-5]