Abstract
Objectives:
This study aimed to investigate the efficacy of St. John's wort extract (SJW) as a treatment for premenstrual symptoms.
Design:
The study was a randomized, double-blinded, placebo-controlled trial, with two parallel treatment groups. After a no-treatment baseline cycle, volunteers were randomized to either SJW or placebo for a further two menstrual cycles.
Settings/location:
A postal trial conducted from The University of Reading, Berkshire, England.
Subjects:
One hundred and sixty-nine (169) normally menstruating women who experienced recurrent premenstrual symptoms were recruited onto the study. One hundred and twenty-five (125) completed the protocol and were included in the analysis.
Interventions:
Six hundred milligrams (600) mg of SJW (standardized to contain 1800 µg of hypericin) or placebo (containing lactose and cellulose).
Outcome measure:
A menstrual diary was used to assess changes in premenstrual symptoms. The anxietyrelated subgroup of symptoms of this instrument was used as the primary outcome measure.
Results:
After averaging the effects of treatment over both treatment cycles it was found that there was a trend for SJW to be superior to placebo. However, this finding was not statistically significant.
Conclusion:
The possibility that this nonsignificant finding resulted from insufficient statistical power in the study, rather than a lack of efficacy of SJW, is discussed. Following this discussion the recommendation is made that, in future, similar studies should be powered to detect a minimum clinically relevant difference between treatments.
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