Amitriptyline is used for:

The relief of depression. It may also be used to treat chronic pain and other conditions as determined by your doctor.

Amitriptyline is a tricyclic antidepressant. How tricyclic antidepressants improve depression symptoms is not fully understood. They are thought to increase the activity of certain chemicals in the brain (norepinephrine, serotonin), which help improve mood...