Presenting a sham treatment as personalised increases the placebo effect in a randomised controlled trial.

Abstract

Tailoring interventions to patient subgroups can improve intervention outcomes for various conditions. However, it is unclear how much of this improvement is due to the pharmacological personalisation versus the non-specific effects of the contextual factors involved in the tailoring process, such as the therapeutic interaction. Here, we tested whether presenting a (placebo) analgesia machine as personalised would improve its effectiveness. We recruited 102 adults in two samples (<i>N₁</i>=17, <i>N₂=</i>85) to receive painful heat stimulations on their forearm. During half of the stimulations, a machine purportedly delivered an electric current to reduce their pain. The participants were either told that the machine was personalised to their genetics and physiology, or that it was effective in reducing pain generally. Participants told that the machine was personalised reported more relief in pain intensity than the control group in both the feasibility study (standardised <i>β</i>=-0.50 [-1.08, 0.08]) and the pre-registered double-blind confirmatory study (<i>β</i>=-0.20 [-0.36, -0.04]). We found similar effects on pain unpleasantness, and several personality traits moderated the results. We present some of the first evidence that framing a sham treatment as personalised increases its effectiveness. Our findings could potentially improve the methodology of precision medicine research and inform practice. This study was funded by the Social Science and Humanities Research Council (93188) and Genome Québec (95747).