Depression is a common, recurring illness that continues to be underdiagnosed and undertreated in both psychiatric and primary care settings. It is increasingly being recognized that painful physical symptoms, which commonly exist comorbid with depressive disorders, play a role in complicating diagnosis of depression. Patients tend to discuss physical pain with primary care physicians and emotional pain with psychiatrists, often oblivious to the fact that both may be aspects of one disorder. Those who present with somatic complaints are three times less likely to be accurately diagnosed than patients with psychosocial complaints. However, thorough evaluation of mood and anxiety disorders in primary care is sparse due to the limited time primary care physicians can spend with each patient. Better recognition and treatment of both physical and emotional symptoms associated with mood disorders may increase a patient's chance of achieving remission, which is the optimum therapeutic goal.

Abnormalities of serotonin and noradrenaline are strongly associated with depression and are thought to play a role in pain perception. Brain-derived neurotrophic factor, which is increased with antidepressant treatment, appears to influence regulation of mood and perception of pain. Clinical evidence indicates that dual-acting agents may have an advantage in modulating pain over those agents that increase either serotonin or noradrenaline alone. The novel dual-acting agents, such as venlafaxine and duloxetine, are better tolerated than tricyclic antidepressants and monoamine oxidase inhibitors. These agents have demonstrated efficacy in depression and in diabetic neuropathic pain independently. Therefore, unless otherwise stated, all inferences to studies of pain in this monograph refer to neuropathic pain in nondepressed patients.