Benefits
Hot flashes and overall menopausal symptoms
A meta-analysis of 22 randomized trial reports (2,310 women), some using black cohosh combined with other ingredients, found it improved hot flashes and overall menopausal symptoms more than placebo. A review of 16 trials of black cohosh alone found no significant difference from placebo for hot flashes, and three US placebo-controlled trials (89 to 351 women, up to 1 year) did not reduce hot flashes more than placebo.
Physical menopausal symptom scores
In the 22-trial meta-analysis, overall and physical (somatic) symptom scores improved versus placebo. A pooled analysis limited to the isopropanolic extract (iCR) also reported benefit, but two of its authors work for the extract's maker. A review of 16 trials of black cohosh alone found no significant difference from placebo in menopausal symptom scores.
Mood symptoms during menopause
The 22-trial meta-analysis found no significant improvement in anxiety or depressive symptoms versus placebo. A review of the isopropanolic extract (iCR), coauthored by the maker's staff, reports benefit for psychological symptoms, larger when combined with St John's wort. Do not rely on black cohosh for mood.
Not shown to act as an estrogen
In rats, a black cohosh extract did not change uterine weight or vaginal cells, signs of estrogen action; in women, a 12-month trial and a maker-coauthored review report unchanged hormone levels. A 132-woman trial whose rationale centered on hot flashes after breast cancer treatment found no benefit over placebo. People with hormone-sensitive conditions should consult their doctor first.
Mechanism of action
Serotonin receptor activity
In laboratory tests, a black cohosh extract bound human serotonin 5-HT1A, 5-HT1D and 5-HT7 receptors and acted as a partial agonist at 5-HT7, receptors tied to the hypothalamus, which is implicated in hot flashes. This proposed explanation has not been shown in people; the EU monograph states the mode of action is unknown.
No estrogen-like effect in animal tests
In ovariectomized rats, a black cohosh extract did not raise uterine weight or change vaginal cells, alone or with estradiol, indicating no estrogenic or anti-estrogenic action in that model. A review of the iCR extract, coauthored by the maker's staff, reports unchanged hormone levels and no effect on breast or endometrium in clinical studies.
Clinical trials
Pairwise meta-analysis of randomized controlled trials of black cohosh extracts alone or combined with other ingredients; a pooled analysis, not a new trial. (Sadahiro et al. 2023, Menopause)
22 articles with 2,310 menopausal women.
Compared with placebo, black cohosh improved overall menopausal symptoms (Hedges' g 0.575), hot flashes (g 0.315) and somatic symptoms (g 0.418), but not anxiety (g 0.194, p = 0.438) or depressive symptoms (g 0.406, p = 0.131). Dropout rates were similar to placebo.
Systematic review of randomized trials of oral black cohosh versus placebo or active treatments, searched to March 2012; not a new trial. (Leach et al. 2012, Cochrane Database Syst Rev)
16 trials with 2,027 perimenopausal or postmenopausal women; median dose 40 mg a day for an average of 23 weeks.
No significant difference from placebo in hot flash frequency (3 trials, 393 women) or menopausal symptom scores (4 trials, 357 women). Hormone therapy reduced symptom scores more than black cohosh. The authors concluded the evidence was insufficient to support its use and trial quality was generally unclear.
1-year randomized, double-blind, placebo-controlled trial of black cohosh 160 mg a day, two multibotanical regimens, hormone therapy or placebo. (Newton et al. 2006, Ann Intern Med)
351 women aged 45 to 55 with at least 2 vasomotor symptoms a day.
Vasomotor symptom frequency and intensity did not differ between black cohosh and placebo at 3, 6 or 12 months. Hormone therapy reduced symptoms by about 4 per day versus placebo.
Phase III randomized, double-blind, placebo-controlled crossover trial with two 4-week periods of black cohosh 20 mg twice daily or placebo. (Pockaj et al. 2006, J Clin Oncol)
132 women with hot flashes, in a trial framed around women undergoing or finished with breast cancer treatment.
Hot flash scores fell 20% on black cohosh and 27% on placebo (P = .53); frequency fell 17% versus 26% (P = .36). Side effects were minimal. The authors found no evidence that black cohosh reduced hot flashes more than placebo.
Systematic review and meta-analysis of clinical studies of the isopropanolic black cohosh extract iCR; two authors are employees of Schaper & Brümmer, the extract maker. (Castelo-Branco et al. 2021, Climacteric)
35 clinical studies and one meta-analysis covering 43,759 women, 13,096 treated with iCR.
Compared with placebo, iCR improved neurovegetative and psychological menopausal symptoms (standardized mean difference -0.694, p < 0.0001), with larger effects at higher doses. Adverse events were similar to placebo, no evidence of liver toxicity was found in the clinical data, and hormone levels were unchanged.
Randomized, double-blind, four-arm trial of a standardized ethanolic black cohosh extract 128 mg a day (7.27 mg triterpene glycosides) for 12 months; NIH-funded, with extracts prepared by Pureworld (now Naturex) and capsules made by Pharmavite, for which one author was a paid consultant. (Geller et al. 2009, Menopause)
89 women with at least 35 vasomotor symptoms a week, randomized to black cohosh, red clover, hormone therapy or placebo.
Vasomotor symptoms fell 34% on black cohosh and 63% on placebo; only hormone therapy differed significantly from placebo, and other menopausal symptoms generally did not improve. Liver enzymes did not rise and hormone levels were unchanged on black cohosh.