A
Tier
Thymic immune-modulating peptide with extensive clinical use abroad.
Immune Support
Peptide, 28 amino acids
WADA Status:
Not listed
Human Trial Scoreboard
Completed human RCTs
Over 30 in a 2024 review
Largest Human Study
TESTS Phase 3, BMJ 2025
Longest exposure
6 to 12 month courses
Most Recent Trial
COVID-19 era
Description
Thymosin alpha-1 is a twenty eight amino acid peptide isolated from the thymus gland in the 1970s and made synthetically as thymalfasin. It modulates immune function rather than simply stimulating it. It is approved in more than thirty five countries for chronic hepatitis B under the brand Zadaxin, and its situation is unusual: it is not FDA approved, and the reason appears to be commercial rather than scientific. The molecule cannot be patented, so no company has the incentive to fund the very expensive trials US approval requires. Substantial trials exist, including a Phase 3 study in sepsis enrolling one thousand one hundred and six patients published in 2025, and a 2025 meta-analysis pooled eleven trials and one thousand nine hundred and twenty seven patients.
What Are The Claims
Claims made for this compound: Enhances T-cell, dendritic, and NK cell function; Relatively strong evidence base for its category; Approved abroad for hepatitis and immune support
Evidence
This has the strongest evidence base of anything in the immune section and among the strongest in the database. Dinetz and colleagues, writing in Alternative Therapies in Health and Medicine in 2024, note approval across more than 35 countries with over 30 clinical trials involving more than 11,000 human subjects documenting its safety profile. The gap is one of indication rather than quality. That evidence sits in hepatitis and oncology-adjunct settings. The broad immune-optimization and longevity marketing extends well past what those trials examined.
Evidence Strength
Moderate-to-Strong for hepatitis B (approved abroad; not FDA)
Caveats
Approved as Zadaxin/thymalfasin in many countries; NOT FDA-approved; immune/COVID/anti-aging claims outrun the data.
Safety
Alternative Measures
Legal Status
US
Not approved; compounding status under review
UK
Not approved
EU
Not centrally approved
AU
Not approved
WADA
Not listed
Approved in more than 35 countries as Zadaxin, or thymalfasin, for chronic hepatitis B, hepatitis C, and as an immune adjuvant. Not FDA-approved in the United States. Placed in FDA Category 2 in September 2023 and removed from Category 2 effective 27 September 2024 following withdrawal of the nomination.
Citations
Dinetz E et al. (2024). Alternative Therapies in Health and Medicine. Review noting approval in 35+ countries, 30+ clinical trials, 11,000+ subjects. | FDA 503A Category 2, September 2023; removed 27 September 2024.