The uncontrollable placebo effect

Abstract

Objective: To analyse the role of the control group in the methodology of clinical placebo effect evaluating trials.

Setting: Department of Medical Philosophy and Clinical Theory, University of Copenhagen.

Methods: A theoretical methodological analysis.

Results: At least with present trial designs, it is impossible, with certainty, to exclude a potential placebo effect from the so-called control group. The placebo effect, in other words, is uncontrollable.

Conclusion: I suggest that the notions of control group and placebo treatment group are replaced by the notions of "placebo effect maximising group" and "placebo effect minimising group", thus stressing the fact that what such trials measure is a relative effect, and an underestimation of the absolute placebo effect. The illusion of absolute placebo effect evaluation must be acknowledged when articles referring to empirical trials on the placebo effect are interpreted.