Commentaries| Volume 47, ISSUE 8, P733-735, April 15, 2000

Are drug and placebo effects in depression additive?

  • Irving Kirsch
    Address reprint requests to Irving Kirsh, Ph.D., Professor of Psychology, University of Connecticut, Dept. of Psychology, U-20, Storrs, CT 06269-1020
    University of Connecticut, Department of Psychology, U-20 Storrs, CT 06269-1020, USA
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      Meta-analyses indicate that between 65% and 80% of the response to antidepressant medication is duplicated by placebos. These data indicate that if the effects of medication and placebos are additive, then the antidepressant drug effect is relatively small; however, data on other drugs indicate that placebo and drug effects are not always additive. Because drug effects are estimated as the difference between the drug response and the placebo response, the assumption of additivity is implicit in conventional clinical trials. The additivity of drug and placebo effects of antidepressant medication needs to be assessed empirically. If these effects are found not to be additive, alternative designs will be needed to assess drug effects.
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