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The efficacy of antidepressant treatment over placebo for major depressive disorder "varies considerably,'" depending upon symptom severity, according to a meta-analysis.
Only patients whose depression is classified as "very severe" appear to have a greater benefit from antidepressants than from placebo pills, according to the study by Jay C. Fournier of the University of Pennsylvania, Philadelphia, and his colleagues (JAMA 2010;303:47-53).
Most placebo-controlled studies of antidepressants specifically exclude individuals who score below 23 on the Hamilton Depression Rating Scale (HDRS). HDRS scores of 8-13 indicate mild depression, scores of 14-18 indicate moderate depression, scores of 19-22 indicate severe depression, and scores of 23 or above indicate very severe depression.

