Intended for healthcare professionals


Informed consent and clinical trials: where is the placebo effect?

BMJ 2017; 356 doi: (Published 03 February 2017) Cite this as: BMJ 2017;356:j463
  1. C R Blease, philosopher of medicine1 2,
  2. F L Bishop, health psychologist3,
  3. T J Kaptchuk, director2
  1. 1School of Philosophy, University College Dublin, Ireland
  2. 2Program in Placebo Studies, Beth Israel Deaconess Medical Center/Harvard Medical School, Boston, MA, USA
  3. 3Department of Psychology, University of Southampton, UK
  1. Correspondence to: C R Blease charlotteblease{at}

Lack of knowledge about placebos affects participants’ understanding of trials and breaches the ethical obligations of researchers, argue C R Blease, F L Bishop, and T J Kaptchuk

Informed consent requires researchers to provide participants with information about research that is accurate, complete, and understandable.1 Researchers also have an ethical obligation to ensure participants understand the investigational nature of the study. In clinical trials we argue that adequate information must include understandable descriptions of the function of placebos2 and their effects (box 1). This is essential to ensure trial participants are fully informed about the potential benefits and risks of the study. The ethical imperative to ensure that participants understand placebos is made stronger by continued debate about use of placebos and active controls.4

Box 1: What are placebos?3

According to typical patient information leaflets used in clinical trials: “A placebo is a dummy treatment which looks like a genuine medicine but contains no active ingredient.”

Placebos are designed to look—and ideally taste, smell, and feel—like the drug that is being tested so that participants do not know which they are receiving. Placebos are often made out of substances such as cellulose, flour, or lactose.

Can placebo treatment have any positive benefits?

There is evidence that placebos have measurable effects on many symptoms, including pain, depression, fatigue, and other perceptions of bodily dysfunction. When patients receive attention from medical professionals about their symptoms, and then receive a treatment (even if that treatment is a placebo), the brain’s natural pharmacy is activated releasing neurotransmitters and engaging areas of the brain that help to relieve symptoms. Evidence suggests that placebo effects mainly involve relief of symptoms but are unlikely to affect underlying disease

Nevertheless, evidence suggests that investigators often fall short of their ethical obligations. In the 1980s the term “therapeutic misconception” was coined to refer to the widespread …

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