Antidepressants in chronic pain.

ADs have achieved popularity in the treatment of chronic pain syndromes associated with organic and psychogenic illness. This is surprising as there is little evidence from controlled studies that they are of value other than in the treatment of depression. There is good evidence for an intimate relationship between the neurotransmitters involved in the regulation of pain and mood and the mode of action of both opiates and antidepressants. There are also similarities in the clinical pharmacology of both groups of drugs, including evidence of a co-analgesic action when ADs are used in conjunction with opiates. Uncontrolled studies suggest that, when ADs have been reported to relieve pain when used alone, this is consequent on relief of depression. Their reported effectiveness in neuralgic pain appears to be dependent on being used in conjunction with a phenothiazine. Controlled studies do not support their use in chronic pain other than for relief of depression. Overall, it may be said that they have a useful opiate-potentiating role in pain due to cancer, are valuable in treatments of neuralgia when given with a phenothiazine, and, in other conditions, may relieve depression-associated pain by their AD action. New AD drugs with specific effects on MA metabolism may reveal if ADs have an analgesic action independent of their AD effect and suggest its biochemical basis. This would have important implications for improving knowledge of pain biochemistry and physiology. Few areas of modern therapeutic endeavour allow prescription of drugs in the absence of objective evidence of benefit. Current practice in chronic pain reflects the problems associated with psychological assessment in chronic physical illness, the complexity of chronic pain syndromes, and the natural desire to explore every avenue to relieve patients' symptoms.