A Cochrane review included 43 trials involving a total of4 364 women comparing phytoestrogens with control. Very few trials had data suitable for combining in meta-analysis. There was no significant difference between Promensil (a red clover extract) and placebo either in the frequency of hot flushes (mean difference (MD) -0.93, 95% CI -1.95 to 0.10; I²=31%, 5 trials) neither in percentage reduction in hot flushes (MD 20.15, 95% CI -12.08 to 52.38, I²=82%, 2 trials). Some of the other trials found phytoestrogens alleviate hot flushes and night sweats but many of the trials were of low quality and underpowered. There was a strong placebo effect in most trials with a reduction in frequency ranging from 1% to 59% with placebo. There was also no evidence that the treatments caused oestrogenic stimulation of the endometrium when used for up to two years.
Comment: The quality of evidence is downgraded by study quality (very variable quality), by inconsistency (variability in results across studies and heterogeneity in interventions and outcomes), and by indirectness (differences in studied patients).