Background and objectives: Hot flashes are one of the most predominant complaints of menopause among women. The main treatment is hormone replacement therapy, which has side effects. Therefore, the use of plants with phytoestrogen has been suggested as an adjunctive treatment. This study aimed to estimate the efficacy of processed rhubarb (Rheum ribes L.) on hot flashes in postmenopausal women. Methods: This double-blind placebo-controlled trial was performed on postmenopausal women who were referred to public health centers at Iran University of Medical Sciences. Ninety postmenopausal women aged over 45 years with menopausal hot flashes were randomly assigned to two groups. The treatment group received 500 mg of encapsulated processed R. ribes twice a day for eight weeks, and the control group received placebo (starch powder) in the same manner. Data were collected using Blatt–Kupperman index at the start of the study, fourth and eighth weeks after the intervention. Descriptive and analytic statistics were used to analyze the data. Results: A total of 74 patients completed the study (39 participants in the intervention group and 35 in the control group). The results showed that R. ribes significantly decreased the mean of flashing in Blatt–Kupperman index four and eight weeks post-intervention (p<0.001). Rheum ribes showed no serious adverse effects. Conclusion: The findings of this study propose that treatment with R. ribes may be considered an adjunctive treatment for hot flashes in postmenopausal women
