Author's Reply to Commentary on No effect of 'Hypericum perforatum' (St John's wort) and 'Vitex agnus-castus' (chaste tree) combination on menopausal symptoms

Abstract

As pointed out in the commentary, there are considerable demands on resources in conducting an RCT of this nature. A four-arm trial investigating the effects of 'V. agnus-castus' and 'H. perforatum' as sole agents would have required a major increase in sample size to ensure statistical power. This presented feasibility constraints with funding and recruitment. Therefore, the combination was tested, with a view to examining individual herbs if a positive result was obtained. Further points of interest have been raised in the commentary. The observation of effect modification of lack of previous herb use cannot be readily explained. However, it is unlikely to reflect negative bias among previous users, as this would not support their voluntary enrolment in such a study. Substantial placebo effects are common in studies of menopausal symptoms, as pointed out. This can necessitate the allocation of increased resources and lead to type II errors (inappropriate rejection of potentially valuable treatment). Increasing our understanding of the placebo response is therefore of great importance. Predictors of the placebo response were examined in this study and will be the subject of future analyses and publications. Participants for the study were sourced from the general community, recruited predominantly though advertisements in the media.