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AIMThis study aimed to quantitate the efficacy of soy isoflavones in the treatment of menopausal hot flashes. METHODSModel based meta-analysis (MBMA) was used to quantitate the efficacy of soy isoflavones. We conducted a systemic literature search to build a time-effect model for placebo and soy isoflavones in treating menopausal hot flashes. Studies were identified, subjected to inclusion and exclusion criteria, and reviewed. RESULTSFrom 55 articles, 16 studies of soy isoflavones met the inclusion criteria, and contained 65 and 66 mean effect values in placebo and soy isoflavone groups, respectively, from about 1710 subjects. Interestingly, the developed model was found to describe adequately the time course of hot flashes reduction after administration of placebo and soy isoflavones. Using this model, we found that the maximal percentage change of hot flashes reduction by soy isoflavones was 25.2% after elimination of the placebo effect, accounting for 57% of the maximum effects of estradiol (E max-estradiol = 44.9%). However, a time interval of 13.4 weeks was needed for soy isoflavones to achieve half of its maximal effects, much longer than estradiol, which only required 3.09 weeks. These results suggest that treatment intervals of 12 weeks are too short for soy isoflavones, which require at least 48 weeks to achieve 80% of their maximum effects. CONCLUSIONSSoy isoflavones show slight and slow effects in attenuating menopausal hot flashes compared with estradiol. WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• Menopause hot flashes can be effectively treated with hormone replacement therapy (HRT). However, possible adverse effects of long term HRT have promoted the use of complementary therapies by menopausal women.• There has been debate on the benefits of soy isoflavones in the treatment of menopausal hot flashes. WHAT THIS STUDY ADDS• The effects of soy isoflavones on menopausal hot flashes was quantitated adequately by the model based meta-analysis. • The developed model provided the robust evidence that soy isoflavones have slight and slow effects in attenuating menopausal hot flashes compared with estradiol.

The placebo response for menopausal hot flashes was related to the active comparator; a higher response rate was observed in trials of hormonal drugs than in trials of nonhormonal drugs. These findings suggest that subjective expectations affect the treatment efficacy of menopausal hot flashes.