Oseltamivir treats flu (influenza) by preventing the viruses causing the infection from spreading once they are inside your body. This reduces the symptoms of the influenza infection. It also reduces the risk of other problems which can sometimes occur alongside flu, such as pneumonia. It is most effective when it is started within an hour or two of the first symptoms of infection, but it can still be effective after this time, as long as it is started within 48 hours of the first symptoms.
This is a companion discussion topic for the original article at https://patient.info/medicine/oseltamivir-capsules-and-suspension-tamiflu-ebilfumin