• Andrew L Geers, Suzanne G Helfer, Kristin Kosbab, Paul E Weiland, and Sarah J Landry.
• Department of Psychology, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606-3390, USA. ageers@utnet.utoledo.edu
• J Psychosom Res. 2005 Feb 1; 58 (2): 121-7.

ObjectivePrior investigations have failed to find reliable personality differences in placebo responding. The present study tests the hypothesis that personality and situational variables interact to determine placebo responding.MethodsOptimists and pessimists were randomly assigned to one of three conditions. In the first condition, the participants were told that they were to ingest a pill that would make them feel unpleasant (deceptive-expectation group). In the second condition, the participants were told that they were to ingest a pill that would make them feel either unpleasant or was an inactive substance (conditional-expectation group). Finally, a third group was told they were to ingest a pill that was inactive (control group).ResultsPessimists were more likely than optimists to follow a negative-placebo expectation when given a deceptive expectation, but not when given a conditional expectation.ConclusionThe personality variable optimism-pessimism relates to placebo responding when individuals are given a deceptive but not a conditional expectation. This suggests that personality and situational variables interact to determine placebo responding.

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