Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) commonly prescribed for depression and anxiety disorders. SSRIs work by blocking the reabsorption (reuptake) of serotonin in the brain, increasing its availability. Other options such as amitriptyline (a tricyclic antidepressant), diazepam (a benzodiazepine), and phenelzine (a monoamine oxidase inhibitor) do not belong to the SSRI class.