Appraisal of drug therapy for nausea and vomiting of pregnancy: I. The placebo effect - Methodological and practical considerations

BACKGROUND: Despite that nausea and vomiting of pregnancy (NVP) is the most common medical problem during pregnancy, the placebo effect in the treatment of this condition has not been properly evaluated. METHODS: Two published randomized, controlled trials comparing the antiemetic effects of vitamin B6 with placebo were analyzed. RESULTS: When the severity of nausea or vomiting in the placebo groups at baseline was compared with that at the end of the trials, there was a clear time-dependent placebo effect that peaked between days 4 and 5. The placebo effect appeared to be more pronounced in nausea than in vomiting. CONCLUSIONS: There is a clear placebo effect on NVP. The effect appears to be stronger with nausea than with vomiting.