The story of placebo effects in medicine: evidence in context

Abstract

In 2005, in an article reviewing the evidence related to the placebo effect that was derived from clinical trials in medicine and psychotherapy, B. E. Wampold, T. Minami, S. C. Tierney, T. W. Baskin, and K. S. Bhati re-analyzed studies contained in A. Hróbjartsson and P. C. Gøtzsche's (2001) meta-analysis of trials that contained placebo and no-treatment conditions. Whereas Hróbjartsson and Gøtzsche (2001) concluded that the placebo effect was weak at best, Wampold et al. (2005) concluded that it was "robust." Hróbjartsson and Gøtzsche (this issue) challenged Wampold et al.'s (2005) conclusion, claiming essentially that the results of clinical trials containing placebo and no-treatment conditions are not sufficient to claim that the placebo effect exists to any substantial degree. In this article, it is shown that when properly interpreted by considering theory, method, context, and related research, the results of clinical trials support the existence of a placebo effect. In short, the placebo effect appears in those instances where it is expected.