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.
Thymosin Alpha-1 has moderate clinical evidence but is not FDA-approved.
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.
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.
Cited sources
Every claim on this page links to one of the 5 sources below. Identifiers are PubMed (PMID), ClinicalTrials.gov (NCT), or DOI; click through to the source of record before acting on a claim.
- 1PMID 39814420PubMed
- 2The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trialReference
- 3Systematic review and meta-analysis of thymosin α-1 in sepsisReference
- 4NCT06821100ClinicalTrials.gov
- 5Thymosin Alpha 1 (Tα1) -- A Peptide for Use in the Treatment of Viral Diseases (comprehensive review)Reference