Oseltamivir is an antiviral medication commonly used to treat and prevent influenza, commonly known as the flu. It works by inhibiting the enzyme neuraminidase, which is essential for the flu virus to spread within the body. By blocking this enzyme, oseltamivir helps to reduce the severity and duration of flu symptoms when taken early in the infection. This medication is available in capsule and liquid form and is typically prescribed for adults and children over the age of two. It is most effective when taken within the first 48 hours of flu symptoms. While oseltamivir can help manage flu symptoms, it is not a substitute for the flu vaccine, which is the best way to prevent influenza.