Antidepressant drug. Close-up of an 81-year-old woman handling a blisterpack containing capsules of the antidepressant drug fluoxetine, commonly known as Prozac. This is a member of the selective serotonin reuptake inhibitor (SSRI) class of drugs. It is used to treat major depressive disorder, as well as other mental disorders. The packaging shown here is labelled with the days of the week to help the patient take the drug at the correct times and the correct frequency.