Thymosin Alpha-1: research, legal status and who sells it

What it is

Thymosin alpha-1 (thymalfasin) is a synthetic polypeptide that modulates the immune system, thought to work by enhancing T-cell function [9].

Research status

Trials in chronic hepatitis B and C produced mixed results: one randomized trial in hepatitis B reported viral DNA clearance in 40.6% and 25.6% of patients in its two treatment groups, versus 9.4% of untreated controls, but effects on illness and death remained unclear [9]. It was generally well tolerated in these studies [9]. In a 361-patient trial in severe sepsis conducted in China, 28-day mortality was 26.0% with thymosin alpha-1 versus 35.0% without it, a difference of borderline statistical significance (relative risk 0.74, 95% confidence interval 0.54 to 1.02) [10]. A 2025 review describes interest in its use against age-related immune decline, including improved vaccine responses in older people, but says further research is needed to establish long-term efficacy and safety [11].

Regulatory status

Thymalfasin is authorized nationally in Italy as Zadaxin; there is no EU-wide authorization [4][5]. It is not FDA-approved, and its nomination for pharmacy compounding was withdrawn after FDA said the safety information was inadequate to understand its risks [1][2]. No thymalfasin medicine is authorized in the UK or Canada [3][6]. It is not named in Australia’s Poisons Standard [7] or on WADA’s 2026 Prohibited List [8].

Quality and testing considerations

FDA cites potential immunogenicity and complexities with peptide-related impurities and characterization of the active ingredient [2]. Research-chemical thymosin alpha-1 is not the Italian authorized product, so its identity, purity and sterility are unknown unless independently tested.

Where it’s sold

Outside Italy’s authorized product, thymosin alpha-1 is sold by research-chemical vendors; the tables below track listings.