The placebo response and effect of time in a trial of acupuncture to treat nausea and vomiting in early pregnancy

Abstract

Objectives: The sham control is widely used in acupuncture research, and its adequacy may be assessed by exploring the 'credibility' of the intervention. We aimed to examine the credibility of the study intervention, to quantify the size of the placebo response and effect of time in reducing nausea in early pregnancy.

Design: Five hundred and ninety-three women with nausea or vomiting in early pregnancy volunteered to participate in a randomised controlled trial, conducted at the Women's and Children's Hospital, South Australia.

Outcome measures: Women completed the Rhodes Index of Nausea and Vomiting and the Credibility Rating Scale.

Results: The credibility of the acupuncture and sham acupuncture interventions were not different. The relative change in nausea at the end of the first week of the study was estimated to be 28% attributed to a time effect and 7% to the placebo response. At the end of the third week, there was a further small increase in time effect (32%) and the placebo response (17%).

Conclusion: Sham acupuncture is a credible control and allows assessment of the size of the placebo response.