so when the flu hits, call your doctor right away and up the ante with antiviral tamiflu. prescription tamiflu is an antiviral that attacks the flu virus at its source and helps stop it from spreading in the body. tamiflu is fda approved to treat the flu in people two weeks of age and older whose flu symptoms started within the last two days. before taking tamiflu, tell your doctor if you're pregnant, nursing, have serious health conditions, or take other medicines. if you develop an allergic reaction, a severe rash, or signs of unusual behavior, stop taking tamiflu and call your doctor immediately. children and adolescents in particular may be at an increased risk of seizures, confusion, or abnormal behavior. the most common side effects are mild to moderate nausea and vomiting. anti-flu? go antiviral with tamiflu.