Immune & defense Immunomodulatory peptide
Thymosin alpha-1
Regulatory status
Status at a glance
503A compounding status
Not nominated
We found no pending nomination for the 503A bulks list. Unless the substance has another legal pathway (for example, a USP monograph or use in an FDA-approved drug), 503A pharmacies generally may not compound with it.
- FDA approval
- Not FDA-approved for any use
- 503B outsourcing
- Not determined
- Anti-doping (WADA)
- Not on the WADA Prohibited List
- DEA schedule
- Not a controlled substance
About peptide status
Most peptides discussed here are not FDA-approved for any use, and products labeled “research use only” are not for human use. Removal from Category 2 does not authorize compounding. PCAC votes are non-binding recommendations; FDA and HHS make the final decisions.
This is not medical or legal advice, and we do not publish dosing, sourcing or reconstitution information. Talk with a licensed clinician before using any peptide.
If you think you are having a medical emergency, call 911.
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.
At a glance
- FDA status
- Not FDA-approved in the U.S.; approved as thymalfasin (Zadaxin) in many other countries
- What it is
- Immune-modulating peptide originally from thymus extract
- Research
- Real human trials in hepatitis and sepsis, but results are mixed and a key recent trial was negative
- Wellness use
- No evidence for a general wellness or longevity use
- Evidence strength
- Moderate research
Summary
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.
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 countries 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?
Safety note
Status: Not FDA-approved in the U.S.; approved as thymalfasin (Zadaxin) in many other countries
Category: Wellness and performance · Primary body area: Immune & defense
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. Tele Launched does not prescribe, sell, or facilitate access to thymosin alpha-1.
What does the research show?
Editor’s note
Evidence strength: Moderate research (3 human · 0 animal/cell studies)
It has multiple independent human trials and meta-analyses in its studied immune and antiviral uses and is approved outside the United States, but results are mixed, the key recent sepsis trial was negative, and there is no evidence for the general wellness use.
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 trial 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 trial | 361 | Borderline mortality benefit suggested: 26.0% versus 35.0% at 28 days (p = 0.062) |
| Sepsis, larger double-blind Phase 3 TESTS trial | 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 markers. In sepsis, a 2025 meta-analysis 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.x); the ETASS sepsis trial (Wu et al., Critical Care, 2013, DOI: 10.1186/cc11932); the Phase 3 TESTS sepsis trial (BMJ, 2025, DOI: 10.1136/bmj-2024-082583); and a 2025 meta-analysis (Frontiers in Cellular and Infection Microbiology, DOI: 10.3389/fcimb.2025.1673959), 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.
Registered human trials
3 registered human trials on ClinicalTrials.gov that we reviewed
Sources
Compare every peptide’s status in the peptide regulatory status database
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