A comparative study on the effect of “black cohosh” and “evening primrose oil” on menopausal hot flashes

Hot flashes are considered to be a common experience for menopausal women and they can compromise the quality of life. The objective of this study is to assess the efficacy of Cimicifuga racemosa in comparison with evening primrose oil (EPO) in postmenopausal women with menopause‑related symptoms.

This study was performed on 80 postmenopausal women with hot flashes. The participants were randomly divided into two groups by blocked randomization. The participants of one group received black cohosh and the other group received EPO for 8 weeks. The severity and number of hot flashes and quality of life were measured by four‑point scale, and the Menopause‑Specific Quality of Life (MENQOL) questionnaire at pre‑intervention, 1st, 4th, and 8th weeks after treatment. Data were analyzed in SPSS Version 16 using independent t‑test, Chi‑square, and Fisher’s exact test.

Average severity of hot flashes in both groups and number of hot flashes in black cohosh group in 8th week were significantly lower than 1st week (P < 0.001), but number of hot flashes in primrose oil group in 8th week showed no significant differences (P = 0.32). The number of hot flashes and quality of life score in black cohosh arm compared to EPO showed a significant decrease in the 8th week (P < 0.05). All MENQOL scores were significantly improved in two groups (P < 0.05), but the percentage of improvement in black cohosh arm was significantly superior to EPO group.

Both herbs were effective in reduction of severity of hot flashes and improvement of the quality of life, but it seems that black cohosh is more effective than primrose oil because it was able to reduce the number of hot flashes too.