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Describing placebos in patient information leaflets: effects on patients’ beliefs

Felicity L Bishop, Laura McGinn, Cynthia A Graham, Hazel Biggs, Simon Denegri, George T Lewith


Background: There are ethical shortcomings to current standard practices regarding the provision of information about placebos in clinical trials. Written information about placebos for clinical trial participants can be incomplete and even misleading. We aimed to develop accurate yet accessible written information about placebos for patients who might participate in clinical trials and to test the effects of such information on patients’ beliefs about placebos.

Methods: With input from 22 patients and public volunteers, a new, “elaborated” information leaflet was developed to provide accessible and evidence-based information about placebos and their possible effects. A “standard” leaflet was also produced which gave a neutral but incomplete description of placebos. In an online experiment 328 participants with chronic health conditions were randomised to read either the elaborated or the standard leaflet. Participants completed validated measures of the credibility and expected effectiveness of placebo treatment for pain and intentions, attitudes, perceived behavioural control and subjective norms towards taking part in a placebo-controlled trial. 

Results: The elaborated leaflet had a significant positive effect on participants’ ratings of the credibility (t(326) = -2.78, p<0.01) and effectiveness (t(326) = -2.59, p<0.05) of placebo treatment for pain.  It had no effect on intentions to take part in placebo-controlled clinical trials. 

Conclusions: The elaborated leaflet provided more comprehensive information about placebos than is commonly provided in current clinical trials. Such a leaflet appears to have greater ethical validity and might increase the magnitude of placebo effects. Further research is needed with participants who are actively considering enrolling in a placebo-controlled trial.


Evidence-based information, informed consent, patient education, patient information leaflets, person-centered healthcare, placebos, placebo effects, randomized clinical trials, research ethics

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