The antidepressants, amitriptyline and nortriptyline are used for chronic pain, for which they are effective. This probably occurs due to the serotonergic effects of these medication. It is known that the serotonin nerve cells in the part of the brainstem called the peri-aqueductal grey, travel downward into the spinal cord and connect in the spinal cord in specific regions with the nerve pathways carrying pain information from the body, lowering the transmission of pain back upward into the brain.
I hope that you are feeling better! -Eliot Seigle MD