Placebo Effects on Stress, but Not on Pain Reports. A Multi-Experiment Study

• Published in: Frontiers in psychology Vol. 12; p. 639236
• Main Authors: Vambheim, Sara Magelssen, Daniali, Hojjat, Flaten, Magne Arve
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media S.A 07.06.2021
• Subjects: experimenter sex; negative emotions; participant sex; placebo effect; placebo response; Psychology; stress; blood pressure; placebo effect; stress; experimenter sex; participant sex; negative emotions; placebo response
• ISSN: 1664-1078; 1664-1078
• DOI: 10.3389/fpsyg.2021.639236

Contextual factors, such as participant/experimenter sex may moderate the placebo effects. We tested whether the participant and experimenter sex modulated placebo effects on experimentally induced pain and associated stress. To investigate if (i) participant sex and (ii) experimenter sex influence placebo analgesia and subjective and physiological stress in two experiments employing a within-subjects and a mixed design, respectively. Placebo effects were investigated in pain reports, stress, and blood pressure. Participants received painful stimulations and a placebo cream. In ( = 59) participants underwent a placebo condition (PC) and a natural history condition (NHC) in random order. A placebo cream was applied in the PC and then the heat stimulation temperature was surreptitiously lowered. Identical stimulations were administered in the NHC, but with no cream, no information, and no lowered temperature. In , participants ( = 93) were randomly assigned to three groups receiving either a placebo cream with surreptitiously lowered intensity of electric stimuli (Placebo, PG), a placebo cream (Cream-Control, CCG) without changing the stimuli, or lowered intensity, but with no cream (Pain-Control, PCG) in a mixed design. All participants in both experiments received the same stimuli in the post-test as in the pre-test. Four experimenters (two females) in , and five experimenters (two females) in conducted the studies. No placebo effect was seen on pain. However, there were placebo effects on stress, moderated by participant and experimenter sex: in males in the PC had lower diastolic blood pressure (DBP) compared to males in the NHC. Participants in the PC had lower DBP compared to the NHC when tested by a female. In , participants expected more cream effectiveness when a female experimenter administered it, and reported lower stress in the PG compared to the PCG when tested by females. Our findings highlight a distinction between placebo effects on pain and on associated stress. Secondly, female experimenters recorded lower physiological and subjective stress, higher effectiveness expectations, and lower pain from both sexes compared to male experimenters. Possible reasons for the failure to find a pain placebo effect are discussed.