Do antidepressants have an analgesic effect in psychogenic pain and somatoform pain disorder? A meta-analysis

Objective: A significant amount of evidence indicates that some antidepressants have an analgesic effect. We wished to determine whether this analgesic effect could be demonstrated in studies that had used antidepressants for the treatment of pain in patients diagnosed with psychogenic pain or somatoform pain disorder. Meta-analysis was used for this purpose. Methods: All randomized, placebo-controlled antidepressant treatment studies of patients diagnosed with psychogenic pain disorder or somatoform pain disorder were isolated. These studies were reviewed and relevant statistics were coded. For each study, a single p value for the drug/placebo comparison was found or calculated for pain change scores from pretreatment to completion of treatment. The z scores and effect sizes were calculated for each study, followed by a calculation of an overall z score and effect size. Results: Eleven studies fulfilled the inclusion and exclusion criteria for this meta-analysis. The combined difference showed that antidepressants decreased pain intensity in patients with psychogenic pain or somatoform pain disorder significantly more than placebo (z = 5.71, p <.0001). The overall effect size was large (mean = 0.48) and ranged from 0 to 0.91. Conclusions: The results indicate that, in patients diagnosed with psychogenic pain or somatoform pain disorder, antidepressant treatment resulted in a reduction in pain that was significantly greater than that of placebo. Possible explanations for these results are discussed.