Is there a link between chronic pain, chronic stress and depression?

Current depression and chronic pain treatments are not effective in all patients. Studies involving animals have shown that the hypothalamo-pituitary-adrenal (HPA) axis is triggered when there is chronic pain. This axis involves 3 main organs: the hypothalamus (located in the brain), the pituitary gland (located at the base of the brain) and the adrenal glands (found near the kidneys). In animals the triggering of this axis is also linked with symptoms that are similar to those of depression. The results found from human studies of chronic pain and depression show a possible link between the two illnesses. This link could be through chronic stress activating the HPA axis. This review discusses how the HPA axis could be involved in the development of chronic pain and depression. The review also gives ideas of how new treatments could be developed.