Which of the following medications is classified as a selective serotonin reuptake inhibitor (SSRI)?

Prozac is classified as a selective serotonin reuptake inhibitor (SSRI) because it primarily works by increasing the levels of serotonin in the brain by inhibiting its reuptake into neurons. This mechanism helps to alleviate symptoms of depression and anxiety, making SSRIs effective treatments for various mood disorders.

In contrast, the other medications listed have different therapeutic uses and mechanisms of action. Valium is a benzodiazepine used primarily for anxiety and muscle relaxation. Lithium is a mood stabilizer primarily used to treat bipolar disorder. Ritalin is a stimulant often prescribed for attention deficit hyperactivity disorder (ADHD) and works by increasing dopamine levels in the brain rather than primarily affecting serotonin. This differentiation supports the classification of Prozac as an SSRI and highlights its unique role in managing depression and anxiety disorders.