Fluoxetine is a selective serotonin reuptake inhibitors (SSRI) antidepressant. The way this medicine works is still not fully understood. It is thought to positively affect communication between nerve cells in the central nervous system and/or restore chemical balance in the brain. Fluoxetine is used to treat major depressive disorder, bulimia nervosa (an eating disorder) obsessive-compulsive disorder, panic disorder, and premenstrual dysphoric disorder (PMDD). Fluoxetine is sometimes used together with another medication called olanzapine (Zyprexa). to treat depression caused by bipolar disorder (manic depression). This combination is also used to treat depression after at least 2 other medications have been tried without successful treatment of symptoms.