Pain, especially chronic pain, is an emotional condition as well as a physical sensation. It is a complex experience that affects thought, mood, and behavior and can lead to isolation, immobility, and drug dependence. In those ways, it resembles depression, and the relationship is intimate. Pain is depressing, and depression causes and intensifies pain. People with chronic pain have three times the average risk of developing psychiatric symptoms — usually mood or anxiety disorders — and depressed patients have three times the average risk of developing chronic pain.
Almost every drug used in psychiatry can also serve as a pain medication.
The most versatile of all psychiatric drugs, the antidepressants have an analgesic effect that may be at least partly independent of their effect on depression since it seems to occur at a lower dose.
The two major types of antidepressants, tricyclics and selective serotonin reuptake inhibitors (SSRIs), may have different roles in the treatment of pain. Amitriptyline (Elavil), a tricyclic, is one of the antidepressants most often recommended as an analgesic, partly because its sedative qualities can be helpful for people in pain. SSRIs such as fluoxetine (Prozac) and sertraline (Zoloft) may not be quite so effective as pain relievers, but their side effects are usually better tolerated, and they are less risky than tricyclic drugs.
The association of depression with migraine headaches, which affect more than 10% of Americans, is especially close. One study found that over a two-year period, a person with a history of major depression was three times more likely than average to have a first migraine attack, and a person with a history of migraine was five times more likely than average to have a first episode of depression.
Very often, when low energy, insomnia, and hopelessness resulting from depression and anxiety perpetuate and aggravate physical pain, it becomes almost impossible to tell which came first or where one leaves off and the other begins.