Objective: Many laypeople demonstrate excessive sensitivity to negative side effects of medical treatments, which may lead them to refuse beneficial therapies. This Internet-based experiment investigated three possible explanations for such "side effect aversion." One was derived from mental accounting, one examined the mere presence of a side effect, and one focused on computational difficulties. Design: Participants (N = 5,379) were presented with a hypothetical cancer preventive treatment situation that was or was not accompanied by one or two small side effects. The side effects were either beneficial or harmful. In all conditions, the net absolute risk reduction associated with the treatment was 15%. Main Outcome Measures: Participants indicated their willingness to accept treatment and their perceptions of the treatment's effects on their overall cancer risk. Results: Data were consistent only with the "mere presence" explanation of side effect aversion, the idea that side effects act as a strong negative cue that directly affects treatment appraisal. The number of negative side effects did not influence treatment willingness. Conclusion: Side effect aversion is a challenge to informed decision making. Specific mechanisms that produce side effect aversion should be identified.

Original languageEnglish
Pages (from-to)201-209
Number of pages9
JournalHealth Psychology
Issue number2
StatePublished - Mar 2009


  • decision making
  • informed consent
  • risk communication
  • risk perception
  • side effects


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