Zadaxin, whose active ingredient is thymalfasin, is a medication used in the treatment of viral diseases and immunodeficiencies. It has an immunomodulatory action, that is, it helps to modulate the body’s immune system. Zadaxin is administered by intramuscular or subcutaneous injection, and the dosage may vary according to the indication and the individual patient’s response. The medication is prescribed for conditions such as chronic hepatitis B, hepatitis C, genital herpes, primary immunodeficiencies, and certain forms of cancer. It is important to follow medical instructions regarding the correct dosage, appropriate frequency of administration, and duration of treatment.