List of products in the National Drug Code with proprietary name . This long-acting form of fluoxetine is used to treat depression in people who have been successfully treated with the form of fluoxetine that is taken daily. Fluoxetine is a selective serotonin reuptake inhibitor (SSRI). SSRIs work by helping to restore the balance of certain natural substances in the brain (neurotransmitters such as serotonin). Fluoxetine may decrease anxiety, improve your mood, sleep, appetite, and energy level and may help restore your interest in daily living.