Oseltamivir
Oseltamivir is an antiviral drug that inhibits the neuraminidase enzyme of influenza viruses. Blocking that enzyme keeps newly formed virus particles attached to the infected cell, so the infection spreads more slowly through the airway. It is used for influenza, an acute viral infection.
It is taken with food, which makes nausea, the most common complaint, less likely. Timing matters more here than with most drugs: the benefit depends on starting treatment early in the illness, within roughly the first two days of symptoms, and it fades if treatment begins later. The full course is completed even once fever and aches settle, because symptoms improve before viral shedding stops. It does not treat bacterial infection and does not replace vaccination.
Breathlessness, chest pain, confusion, or fever that returns after an initial improvement can mean pneumonia or another complication of influenza and should be seen by a doctor. Unusual behaviour or confusion, particularly in children and adolescents, is also a reason for medical review.
Reference information, not medical advice. Discuss any change with your doctor.