Also known as: Ta1, Thymalfasin, Zadaxin
Half-life: ~2 hours
Thymosin Alpha-1 (Ta1) is a 28-amino-acid peptide originally isolated from thymic tissue that plays a central role in modulating immune function. It enhances T-cell maturation, natural killer cell activity, and dendritic cell function, making it one of the most broadly studied immunomodulatory peptides. Marketed as Zadaxin (thymalfasin), it has been approved in over 35 countries for the treatment of hepatitis B, hepatitis C, and as an immune adjuvant in immunocompromised patients.
The mechanism of action of Thymosin Alpha-1 involves activation of toll-like receptors (TLR2 and TLR9), which stimulate innate immune responses and promote the differentiation of immature T-cells into functional CD4+ and CD8+ subsets. It also enhances the production of cytokines such as interferon-alpha and interleukin-2, amplifying both innate and adaptive immune responses. Unlike immunosuppressants, Ta1 acts as an immunomodulator, restoring balanced immune function rather than broadly suppressing or stimulating the immune system.
Clinical applications span viral hepatitis, cancer immunotherapy adjunct, vaccination enhancement in immunocompromised populations, and general immune support. During the COVID-19 pandemic, Ta1 was used clinically in several countries as supportive therapy for hospitalized patients. Its established safety profile across decades of use in diverse patient populations makes it one of the most clinically validated peptides available.
Thymosin Alpha-1 was first isolated from thymic tissue in the 1970s by Allan Goldstein and colleagues at the University of Texas Medical Branch, later at George Washington University. It was identified as the principal immunoactive component of Thymosin Fraction 5, a partially purified thymic extract. The 28-amino-acid peptide was sequenced in 1977. SciClone Pharmaceuticals developed the synthetic version (thymalfasin) and marketed it as Zadaxin. It was first approved in Italy in the early 1990s for hepatitis treatment. It has since been approved in more than 35 countries, primarily in Asia and Europe, for hepatitis B, hepatitis C, and as an immune adjuvant. During the COVID-19 pandemic, it was used clinically in China and other countries as an immune support therapy.
Thymosin Alpha-1 has one of the most established safety profiles among peptides, backed by decades of clinical use across more than 35 countries. In clinical trials involving thousands of patients, the most common side effect is mild injection site discomfort. Flu-like symptoms may occur during the initial immune activation phase but are typically mild and self-limiting. The peptide has been safely used in immunocompromised patients (hepatitis, HIV, cancer patients undergoing chemotherapy) without significant adverse events. No cases of autoimmune activation or excessive immune stimulation have been consistently reported. The extensive safety record was a factor in its approval in numerous countries.
Dose Range
1000-1600 mcg
Frequency
Twice weekly (SubQ)
Duration
6-12 months
Dose Range
1600 mcg
Frequency
Twice weekly
Duration
6-12 months
Dose Range
1600 mcg
Frequency
Daily for initial phase, then twice weekly
Duration
2-4 weeks acute, then maintenance
Dosing information is for educational purposes only. Consult a healthcare professional before using any peptide.
Typical Vial Size
5 mg
Water Type
Sterile water for injection
Mixing Volume
1 mL
Half-Life
~2 hours
Molecular Weight
3108.3 Da
Zadaxin (pharmaceutical form) is supplied as lyophilized powder with diluent. Store at room temperature before reconstitution. Use immediately after reconstitution. Research-grade Ta1 reconstituted with BAC water may be stored refrigerated for up to 21 days.
FDA Status
Not FDA approved. Granted orphan drug designation for hepatocellular carcinoma and hepatitis B. Multiple clinical trials conducted but no NDA submitted.
Legal Status
Approved as prescription medication in over 35 countries (primarily Asia and Europe). Unregulated research chemical in the USA.
USA
Not approvedFDA has not approved, though it has been granted orphan drug status for certain indications
EU
Approved in some member statesApproved in Italy, not centrally authorized by EMA
UK
Not approvedNot centrally approved by MHRA
Australia
Not approvedNot evaluated by TGA
Russia
ApprovedAvailable for hepatitis and immune support
China
ApprovedWidely used for hepatitis B and as immune adjuvant
Tuthill C, Rios I, McBeath R
Expert Opinion on Biological Therapy (2010)
Comprehensive review of thymosin alpha-1 covering its immunological mechanisms, clinical trial data across hepatitis, cancer, and immune deficiency applications.
View Study →Romani L, Bistoni F, Perruccio K, Montagnoli C, Gaziano R, Bozza S, Bonifazi P, Bistoni G, Rasi G, Velardi A, Fallarino F, Garaci E, Puccetti P
Blood (2007)
Elucidated the mechanism by which Thymosin Alpha-1 activates dendritic cells through TLR9, providing molecular insight into its immunomodulatory properties.
View Study →Serafino A, Pierimarchi P, Pica F, Andreola F, Gaziano R, Moroni N, Garaci E, Sinibaldi Vallebona P
Annals of the New York Academy of Sciences (2012)
Demonstrated the stimulatory effects of Ta1 on innate immune cells including NK cells and macrophages, supporting its role as a broad immunomodulator.
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