Amitriptyline is a tricyclic antidepressant commonly used to treat depression, anxiety disorders, and certain types of chronic pain. It works by increasing levels of neurotransmitters in the brain, such as serotonin and norepinephrine, which helps improve mood and alleviate pain. Additionally, amitriptyline can be prescribed for conditions like migraines and insomnia. It is important to use it under medical supervision due to potential side effects and interactions with other medications.