Amitriptyline is a type of drug called a tricyclic antidepressant. Although these are used for anxiety and depression, lower doses are also widely used to block the long-term (chronic) pain of some conditions.
Chemical changes in the spinal cord and brain (central nervous system) can affect pain regulation and lead to increased pain and distress. Amitriptyline rebalances the chemicals in the central nervous system, which can relieve pain, relax the muscles and improve sleep.
It can also help with any anxiety and depression resulting from the pain, though low doses are not enough on their own to treat severe depression.