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. 2021 Jun 7:12:639236.
doi: 10.3389/fpsyg.2021.639236. eCollection 2021.

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

Sara Magelssen Vambheim  1 , Hojjat Daniali  2 , Magne Arve Flaten  2
Affiliations

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

Sara Magelssen Vambheim et al. Front Psychol. .

Abstract

Background: 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.

Objective: 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.

Methods: Participants received painful stimulations and a placebo cream. In Experiment One (N = 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 Experiment Two, participants (N = 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 Experiment One, and five experimenters (two females) in Experiment Two conducted the studies.

Results: No placebo effect was seen on pain. However, there were placebo effects on stress, moderated by participant and experimenter sex: in Experiment One 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 Experiment Two, 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.

Conclusion: 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.

Keywords: blood pressure; experimenter sex; negative emotions; participant sex; placebo effect; placebo response; stress.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
Overview of the Experiment One. Vertical boxes: spots where subjective stress/arousal (SS) and/or blood pressure (BP) were measured. There was a 5-min break between phases and between conditions. MT, manipulation trial. The placebo condition was presented to 29 participants as the first condition, and to 30 participants as the second condition.
FIGURE 2
FIGURE 2
Diastolic blood pressure for males (left panel) and females (right panel). Male participants had lower DBP in the PC T3 compared to the NHC T3 (left panel). No such placebo response was observed for females (right panel). B, baseline. T1, pre-test. T3, post-test. Blue lines: NHC (N = 30). Red dashed lines: PC (N = 29). Error bars: ±1 SE.
FIGURE 3
FIGURE 3
Diastolic blood pressure recorded by the male (left panel), the female (middle panel) and both male and female experimenters (right panel). Female experimenters (middle panel) recorded lower DBP in PC T3 as compared to NHC T3. B, baseline. T1, pre-test. T3, post-test. Blue lines: NHC. Red dashed lines: PC. Error bars: ±1 SE.
FIGURE 4
FIGURE 4
Overview of the Experiment Two. Vertical boxes: spots where subjective stress/arousal (SS) and/or blood pressure (BP) were measured. A 5-min break was given to participants between phases. P-Control: PCG. Placebo: PG. C-Control: CCG.
FIGURE 5
FIGURE 5
Lower subjective stress was reported to female experimenters (left panel) in the PG T3 (post-test) compared to the female experimenters in the PCG T3. Higher subjective stress was reported to male experimenters (right panel) in the PG T1 (pre-test), compared to male experimenters in T1. T1: pre-test. T2: manipulation trial/control. T3: post-test. Blue lines: CCG. Green dashed lines: PCG. Red dashed lines: PG. Error bars: ± 1 SE.
See this image and copyright information in PMC

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