RESUMO
OBJECTIVES: Recent research has shown that placebos can be effective even if they are openly prescribed to participants. Yet, it is unclear how such "open-label placebos" (OLPs) compare to deceptive placebo (DP) and what the mechanisms of actions are. In this study, we therefore compared 2 versions of OLP to DP and no treatment (NT). MATERIALS AND METHODS: Using a standard heat pain paradigm, 117 healthy volunteers underwent a baseline and a posttreatment pain assessment. With the exception of NT, all groups received an inert placebo cream after the first assessment. OLP was administered by either evoking positive expectancies or by raising hope for placebo analgesia, thus distinguishing for the first time conceptually between expectancy and hope in experimental pain research. The primary outcome was pre-post change in pain tolerance. RESULTS: Increase in pain tolerance was larger in the 3 treatment groups compared with NT, whereas the treatment groups did not differ from each other. Further results showed that participants receiving DP reported a large reduction of subjective pain intensity and unpleasantness, whereas no such reduction was found for the 2 OLP groups. The 2 OLP versions did not differ in terms of their analgesic effects. DISCUSSION: The study provided evidence for traditional placebo analgesia on the basis of deception. For OLP, we found that OLP indeed increased pain tolerance; however, participants receiving OLP were reluctant to report any subjective analgesic effects. Combined with previous studies, the present findings suggest that the effects of OLP are weaker in healthy volunteers than in clinical samples.
