Tamiflu (oseltamivir) is an antiviral medication that blocks the actions of influenza virus types A and B in your body. Tamiflu is used to treat flu symptoms caused by influenza virus in people have had symptoms for less than 2 days. This medicine may also be given to prevent influenza in people who may be exposed but do not yet have symptoms. Tamiflu will not treat the common cold. Tamiflu should not be used in place of getting a yearly flu shot. The Centers for Disease Control recommends an annual flu shot to help protect you each year from new strains of influenza virus.