Oseltamivir is an antiviral drug often preferred in treating viral infections. Its use has increased owing to annual influenza outbreaks and the COVID-19 pandemic. Although its adverse effects are often seen in the gastrointestinal system, it has other adverse effects that can prevent its use, for example, neuropsychiatric events. In this case report, we present a manic episode case caused by the use of oseltamivir.