Which of the following medications is used as an antidepressant?

Sertraline is classified as a selective serotonin reuptake inhibitor (SSRI), a commonly prescribed class of antidepressants. It works by increasing the levels of serotonin in the brain, which can help improve mood and alleviate symptoms of depression. SSRIs like sertraline are often favored for the treatment of major depressive disorder and anxiety disorders due to their efficacy and relatively favorable side effect profile compared to older antidepressants.

The other medications listed serve different primary purposes: atorvastatin is used primarily to lower cholesterol, amphetamines are typically used to treat attention deficit hyperactivity disorder (ADHD) and narcolepsy, and metformin is primarily utilized for managing blood sugar levels in type 2 diabetes. This context helps in differentiating the specific therapeutic uses of these medications, emphasizing why sertraline is the appropriate choice as an antidepressant.