Oseltamivir (acid) is primarily used as an antiviral medication to treat and prevent influenza, commonly known as the flu. It is effective against both influenza A and B viruses. The medication works by inhibiting the neuraminidase enzyme, which is essential for the virus to spread within the body. By blocking this enzyme, it helps reduce the severity and duration of flu symptoms, such as fever, cough, sore throat, and body aches.

It is often prescribed for individuals who have been experiencing flu symptoms for no more than 48 hours. Additionally, it is used as a preventive measure in people who have been exposed to the flu but are not yet showing symptoms, particularly in high-risk groups such as the elderly, young children, and those with compromised immune systems.

In healthcare settings, it is sometimes administered to control flu outbreaks, especially in places like nursing homes or hospitals where the risk of transmission is high. It is available in oral form, making it convenient for both treatment and prophylaxis. However, it is important to note that it is not a substitute for the annual flu vaccine, which remains the most effective way to prevent influenza.