Placebo and Pain: Chapter 20. Conceptualizations and Magnitudes of Placebo Analgesia Effects Across Meta-Analyses and Experimental Studies

The magnitude of placebo analgesia effects has been shown to vary across meta-analyses. The conceptualization of placebo effects, and the way in which they are induced, influence the magnitude of placebo analgesia effects. This has been indicated by meta-analyses and further confirmed by experimental studies. In general, small placebo analgesia effects are found in clinical trials in which placebo is used as a control condition, whereas large effects are found in placebo mechanism studies investigating how expectations and emotional feelings contribute to placebo analgesia effects. At present, meta-analyses are used to investigate the seemingly increasing analgesic effects following placebo administration in clinical trials. Current knowledge about placebo mechanisms could contribute to the investigation of these analgesic effects and thereby help to develop new ways of testing pain medication, which ultimately may be of benefit for pain patients.