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Not FDA-approved
Immune & defense
Thymosin alpha-1
Also called Tα1, thymalfasin
Thymosin alpha-1 is approved as thymalfasin in many countries but not in the U.S. See what human trials show in hepatitis and sepsis, and where results vary.
- Reviewed by
- William Maish, MD MBA MPH, Clinical Product Lead
- Published
- April 18, 2026
- Last updated
- October 5, 2026
Key takeaway
Thymosin alpha-1 is an immune-modulating peptide approved as thymalfasin (Zadaxin) in many countries but not in the United States. In the 2025 TESTS trial of 1,089 patients with sepsis, found 28-day mortality of 23.4% on thymosin alpha-1 versus 24.1% on placebo (hazard ratio 0.99, 95% CI 0.77 to 1.27, p = 0.93). Hepatitis B trials are more encouraging, results are mixed overall, and none of it supports a general wellness use.
What is thymosin alpha-1?
Thymosin alpha-1 (abbreviated Tα1) is a 28-amino acid peptide originally isolated from thymus-gland extract, where immune cells mature. It acts as an immune modulator and is an approved drug in more than 35 countries1 under the name thymalfasin (brand Zadaxin), used for chronic hepatitis and as an immune adjunct. In the United States, it is not approved and is sold through wellness and compounding channels for immune support.
How does it work?
Thymosin alpha-1 modulates the immune system in several ways:
- Influencing the maturation and function of T-cells
- Boosting signals such as interferon-gamma and interleukin-2
- Enhancing natural killer-cell activity, partly through Toll-like receptor pathways
This mechanism is supported by laboratory and clinical immune data, such as improved immune-cell markers in sepsis studies. This describes how it acts on the immune system, separate from whether it improves outcomes in a given condition.
Is it FDA-approved?
No, not in the United States. It is approved and marketed as thymalfasin (Zadaxin) in many other countries for chronic hepatitis B and C and as an immune/vaccine adjunct. It was not among the peptides reviewed favorably at the 2026 FDA compounding advisory meetings. Superpower does not prescribe, sell, or facilitate access to thymosin alpha-1.
What does the research show?
It has real human trials, with mixed results, in specific immune conditions, not general wellness. Three trials report outcome figures.
| Condition and trial | Patients | Result |
| Chronic hepatitis B, randomized trial2 comparing thymosin alpha-1 with no treatment | 98 | Complete virological response reached 40.6% after a 26-week course versus 9.4% in controls (p = 0.004); a 52-week course was not significantly better than control |
| Sepsis, earlier multicenter trial3 | 361 | Borderline mortality benefit suggested: 26.0% versus 35.0% at 28 days (p = 0.062) |
| Sepsis, larger double-blind Phase 3 TESTS trial4 | 1,089 | No mortality benefit: 28-day mortality 23.4% on thymosin alpha-1 versus 24.1% on placebo (hazard ratio 0.99, 95% CI 0.77 to 1.27, p = 0.93) |
In chronic hepatitis B, a separate trial reported modest effects on viral and liver markers5. In sepsis, a 2025 meta-analysis6 found the apparent benefit disappeared in higher-quality studies. So real human efficacy exists for some immune and antiviral uses but is mixed, and none of it supports a general wellness or longevity use.
Sources: a hepatitis B trial (Iino et al., Journal of Viral Hepatitis, 2005, DOI: 10.1111/j.1365-2893.2005.00633.x5); the ETASS sepsis trial (Wu et al., Critical Care, 2013, DOI: 10.1186/cc119323); the Phase 3 TESTS sepsis trial (BMJ, 2025, DOI: 10.1136/bmj-2024-0825834); and a 2025 meta-analysis (Frontiers in Cellular and Infection Microbiology, DOI: 10.3389/fcimb.2025.16739596), all indexed on PubMed. This document is educational, is not medical advice or a health claim, and is not an offer to sell any product.