Short communicationEffectiveness of a placebo intervention on visually induced nausea in women – A randomized controlled pilot study
Introduction
Placebo interventions can improve a variety of symptoms including nausea. In a subgroup meta-analysis of randomized controlled trials, for example, placebo-treated patients developed less nausea than untreated controls [1]. Placebo effects on nausea could also be demonstrated in experimental settings [2], [3], [4].
However, many questions regarding placebo effects on nausea remain unanswered. For example, nausea reduction in women could only be achieved when the placebo intervention was “enhanced” by conditioning, while men responded primarily to verbally suggested improvement [2], [3], [4]. Furthermore, improvements of nausea through placebo interventions could be demonstrated in experimental models using whole-body rotation [2], [3] and galvanic vestibular stimulation [5] but not for paradigms in which nausea was visually-induced [6], [7]. It is unclear whether these findings are generalizable or were due to situational variables, such as the gender of the experimenter, the type of verbal suggestion, or characteristics of the placebo intervention itself [3], [4], [8].
In this pilot study, we tested a new paradigm to investigate placebo effects on visually induced nausea in women. Based on evidence from clinical trials that sham acupuncture is associated with particularly large placebo effects [8], [9], [10], we implemented a sham acupuncture point (acupoint) stimulation technique as the placebo intervention. We hypothesized that sham acupoint stimulation would significantly reduce visually induced nausea as compared to untreated controls.
Section snippets
Methods
Twenty-one healthy women between 18 and 50 years (median 26, IQR 20–30) with a history of motion sickness (score of ≥ 50 in motion sickness questionnaire [11]) and a positive screening for visually-induced nausea (see below) were included in the placebo arm of the study. All participants provided written informed consent and were compensated with 50 EUR. The study protocol was approved by the ethical committee of the Ludwig-Maximilians-University Munich.
Susceptibility for visually induced nausea
Results
Descriptive statistics of outcome variables are displayed in Table 2.
The increase of nausea from baseline to the target period was significantly smaller in the placebo condition, as compared to the natural history condition, indicating a strong placebo effect (main effect of condition, F(1,18) = 43.52, p < 0.001; partial η2 = 0.71; Table 2). Similarly, the increase in SSMS sum scores from baseline to nausea was lower in the placebo condition, as compared to the natural history condition (main effect
Discussion
Results of this pilot study indicate that sham acupoint stimulation is an efficient way to evoke a placebo effect on visually induced nausea in females. Expectation of nausea was significantly lowered by the placebo instructions, indicating successful expectancy manipulation. The effect size of the placebo effect on nausea was large and thus clinically important (partial η2 = 0.71). The majority of participants guessed that they had received active treatment. Confounding factors such as
Conflict of interest statement
The authors have no potential conflicts of interest to disclose.
Acknowledgements
This study was prepared in the context of the Research Unit FOR 1328 of the German Research Foundation (DFG) (ME 3675/1-1). KM received support from the Theophrastus Foundation (Germany) and the Schweizer-Arau-Foundation (Germany).
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