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Effectiveness of a placebo intervention on visually induced nausea in women – A randomized controlled pilot study

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Highlights

  • First evidence for reduction of nausea by suggestive placebo intervention in females.

  • Large effect size indicates clinical importance of the placebo effect on nausea.

  • Positive expectations may contribute to the success of antiemetic treatments.

Abstract

Objective

Improvement of nausea by placebo interventions has recently been demonstrated in clinical trials and experimental settings. 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. It is unclear whether these findings are generalizable or were due to situational variables. In this pilot study, we investigated the effects of sham acupuncture point stimulation and verbal suggestions on visually-induced nausea in a female population.

Methods

In a within-subjects design, 21 healthy female volunteers underwent both a placebo condition and a natural history condition (control condition) in a randomized order on two separate days. On both days, nausea was induced through optokinetic stimulation. On the placebo day, participants received sham acupuncture point stimulation together with positive verbal suggestions of nausea improvement. Expected and perceived nausea severity as well as symptoms of motion sickness were repeatedly assessed.

Results

Twenty participants completed both testing days. Participants developed significantly less nausea on the placebo day compared to the control day (p < 0.001), and the effect size of placebo-induced nausea reduction was large (partial η2 = 0.71). Symptoms of motion sickness were also reduced (p = 0.003). Expectation of nausea decreased following the placebo intervention as compared to no treatment (p = 0.030), indicating successful expectancy manipulation.

Conclusion

Sham acupuncture point stimulation combined with verbal suggestions induced a significant placebo effect on visually-induced nausea in women.

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).

References (17)

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