Black Cohosh

This is the herb’s defining and most-tested indication, and the evidence genuinely conflicts. A 2023 updated pairwise meta-analysis of 22 RCTs (n=2,310) found black cohosh extracts significantly improved overall menopausal symptoms and hot flashes versus placebo, though effect sizes were small (Hedges’ g ≈ 0.32 for hot flashes) ^{1Reference 1Sadahiro et al. · 2023Meta-analysisBlack cohosh extracts in women with menopausal symptoms: an updated pairwise meta-analysisView study →}. An earlier meta-analysis reported a 26% improvement in vasomotor symptoms but with significant heterogeneity between trials ^{3Reference 3Shams et al. · 2010Meta-analysisEfficacy of black cohosh-containing preparations on menopausal symptoms: a meta-analysis of randomised placebo-controlled trialsView study →}, and a large industry review of the isopropanolic extract iCR reported efficacy comparable to low-dose transdermal estradiol ^{4Reference 4Castelo-Branco et al. · 2021Meta-analysisReview & meta-analysis: isopropanolic black cohosh extract iCR for menopausal symptoms — an updateView study →}. Against this, the 2012 Cochrane review of 16 RCTs (n=2,027, median 40 mg/day) found no significant difference from placebo in hot-flush frequency or symptom scores ^{2Reference 2Leach et al. · 2012Systematic reviewBlack cohosh (Cimicifuga spp.) for menopausal symptoms — Cochrane systematic review of randomised controlled trialsView study →}, and two rigorous placebo-controlled trials — the NCCTG Phase III crossover trial (n=132) and a trial in breast-cancer survivors (n=85) — showed black cohosh was no better than placebo ^{6,7Reference 6Pockaj et al. · 2006RCTPhase III double-blind, randomised, placebo-controlled crossover trial of black cohosh for hot flashes (NCCTG N01CC1)View study →Reference 7Jacobson et al. · 2001RCTRandomised trial of black cohosh for hot flashes among women with a history of breast cancerView study →}. A UK NICE network meta-analysis placed it above placebo but below transdermal hormone therapy ^{5Reference 5Sarri et al. · 2017Meta-analysisVasomotor symptoms from natural menopause: a systematic review and network meta-analysis (NICE guideline)View study →}. The most defensible reading: a modest, extract-dependent benefit that is easily lost in well-controlled trials.

Gap: the positive signal is concentrated in manufacturer-sponsored trials of one standardised extract; independent, high-quality trials are frequently null, and results do not generalise to teas or non-standardised products.

Beyond hot flashes, black cohosh is credited with easing the irritability, low mood, and anxiety of the menopausal transition, and there is a plausible serotonergic rationale for this. The iCR review found the extract superior to placebo for neurovegetative and psychological symptoms, with the largest effect when combined with St John’s wort (Hypericum perforatum) ^{4Reference 4Castelo-Branco et al. · 2021Meta-analysisReview & meta-analysis: isopropanolic black cohosh extract iCR for menopausal symptoms — an updateView study →}, and a 2019 meta-analysis reported benefit for anxiety and depression across peri- and postmenopausal women ^{9Reference 9Shahmohammadi et al. · 2019Meta-analysisEfficacy of herbal medicines on anxiety and depression in peri- and postmenopausal women: a systematic review and meta-analysisView study →}. A prospective RCT versus fluoxetine (n=120) found black cohosh reduced Kupperman-index and vasomotor scores more than the SSRI, though fluoxetine did more for formal depression scores ^{8Reference 8Oktem et al. · 2007RCTBlack cohosh and fluoxetine in postmenopausal symptoms: a prospective, randomised trialView study →}. The important counterweight: the 2023 pairwise meta-analysis found no significant improvement in anxiety (g=0.19) or depressive symptoms (g=0.41) ^{1Reference 1Sadahiro et al. · 2023Meta-analysisBlack cohosh extracts in women with menopausal symptoms: an updated pairwise meta-analysisView study →}.

Gap: mood benefit is usually a secondary outcome inside menopause trials, is inconsistent, and the strongest signal requires co-administration of St John’s wort — making it hard to attribute to black cohosh alone.

A distinct, more recent line of human research tests black cohosh as an adjunct to clomiphene citrate for ovulation induction in polycystic ovary syndrome. A randomised trial (n=194) reported that adding Cimicifuga racemosa to clomiphene cycles improved endometrial thickness, hormone profiles, and clinical pregnancy rates (34.8% vs 17.2%) ^{13Reference 13Shahin et al. · 2014RCTAdding Cimicifuga racemosa to clomiphene induction cycles in PCOS improves cycle outcomes and pregnancy rates — randomised trialView study →}. A 2021 systematic review of the PCOS literature found three RCTs reporting improved pregnancy rates with black cohosh plus clomiphene and concluded short-term use appears safe — but flagged serious risk-of-bias concerns and a lack of high-quality evidence ^{14Reference 14Fan et al. · 2021Systematic reviewSystematic review of black cohosh for management of PCOS-related infertilityView study →}. A separate clinical trial (n=100) found no difference in follicle number or endometrial thickness when black cohosh was added to clomiphene ^{15Reference 15Pourhoseini et al. · 2022Clinical trialCimicifuga racemosa with clomiphene for ovulation induction in PCOS: a clinical trialView study →}.

Gap: the supporting trials are small, single-centre, and methodologically weak; black cohosh here is an add-on to a fertility drug, not a standalone treatment, and the null trial tempers the positive ones.

Chronic low-grade inflammation (“inflammaging”) rises after estrogen loss, and several mechanistic studies suggest black cohosh extracts blunt it. A 2025 study showed the Ze 450 extract reduced nitric oxide, IL-1, IL-6, iNOS, HIF-1α and mTOR in LPS-stimulated macrophages and shifted their metabolism from oxidative phosphorylation toward glycolysis ^{16Reference 16Günther et al. · 2025In vitroCimicifuga racemosa extract Ze 450 shifts macrophage immunometabolism and attenuates pro-inflammatory signalling — in vitroView study →}. Bioactivity-guided fractionation earlier identified cimiracemate A as an anti-inflammatory constituent that suppresses LPS-induced TNF-α in human macrophages via MAPK and NF-κB modulation ^{17Reference 17Yang et al. · 2009In vitroIdentification of cimiracemate A as an anti-inflammatory constituent of black cohosh on human macrophages — in vitroView study →}. These findings are coherent but confined to cell systems.

Gap: entirely in vitro; no clinical study has tested black cohosh as an anti-inflammatory agent, and the extracts used (e.g. Ze 450) are proprietary and manufacturer-supplied.

Because postmenopausal women lose bone, black cohosh’s possible skeletal effect has drawn interest, with mixed preclinical results. In human osteoblasts in vitro, the isopropanolic extract raised osteoprotegerin secretion 3–5-fold and improved the OPG-to-RANKL ratio, an effect blocked by an estrogen-receptor antagonist ^{18Reference 18Viereck et al. · 2005In vitroIsopropanolic extract of black cohosh stimulates osteoprotegerin production by human osteoblasts — in vitroView study →}. The isolated triterpene actein stimulated osteoblastic MC3T3-E1 cells and protected them against oxidative mitochondrial damage in vitro ^{19Reference 19Lee et al. · 2014In vitroActein isolated from black cohosh promotes the function of osteoblastic MC3T3-E1 cells — in vitroView study →}, and a 2025 study reported that C. racemosa attenuated bone loss in ovariectomised rats via CB2R and ERα signalling ^{20Reference 20Hu et al. · 2025In vitroCimicifuga foetida and C. racemosa prevent postmenopausal osteoporosis by inhibiting osteoclast autophagy via CB2R and ERα — in vitro and ovariectomised-rat modelView study →}. However, a well-controlled FDA ovariectomised-rat study found black cohosh extract had no effect on bone mineral density, alone or with risedronate ^{21Reference 21Inselman et al. · 2024AnimalBlack cohosh extract and risedronate coadministration on bone health in an ovariectomised rat modelView study →}.

Gap: no human bone-outcome data exist; the animal evidence conflicts, and the Cochrane review specifically listed bone health as an unresolved question.

A body of cell-line work suggests the triterpene glycoside actein has antiproliferative activity, but this is constituent-level pharmacology, not a use of the herb. Actein preferentially inhibited breast-cancer cell growth, triggered ER-mediated calcium release, and modulated NF-κB and MEK pathways ^{23Reference 23Einbond et al. · 2013In vitroActein induces calcium release in human breast cancer cells — in vitroView study →}; it synergised with doxorubicin, 5-fluorouracil and paclitaxel against breast-cancer lines in vitro ^{22Reference 22Einbond et al. · 2006In vitroActein and a fraction of black cohosh potentiate antiproliferative effects of chemotherapy agents on human breast cancer cells — in vitroView study →}; and it inhibited colorectal-cancer cells and a xenograft via the PI3K/Akt pathway ^{24Reference 24Yan et al. · 2021In vitroActein antagonizes colorectal cancer by blocking PI3K/Akt pathways — in vitro and xenograft modelView study →}. The authors themselves note actein is lipophilic with limited bioavailability, and no whole-herb or human oncology data exist.

Gap: confined to isolated actein at supra-physiological concentrations in cell and xenograft models; black cohosh is not used as an anticancer agent, and its hepatotoxicity signal makes high-dose use inadvisable.

Black cohosh is generally well tolerated in short- to medium-term use, with the most common adverse effects being mild gastrointestinal upset, headache, and dizziness ^{26Reference 26Borrelli et al. · 2008Systematic reviewBlack cohosh (Cimicifuga racemosa): a systematic review of adverse eventsView study →}. Its principal safety concern is rare but serious idiosyncratic hepatotoxicity: multiple case reports document drug-induced liver injury, including cholestatic injury and at least several cases of subacute liver failure requiring transplantation ^{28,29Reference 28Lim et al. · 2013Case reportSubacute liver failure secondary to black cohosh leading to liver transplantation — case reportView study →Reference 29Brar et al. · 2021Case reportCholestatic drug-induced liver injury associated with black cohosh — case reportView study →}. Causality in these cases is generally rated only “possible” rather than probable, and meta-analyses of controlled trials of the standardised isopropanolic extract found no measurable effect on liver enzymes ^{25,27Reference 25Naser et al. · 2011Meta-analysisSuspected black cohosh hepatotoxicity: no evidence by meta-analysis of randomised controlled trials for isopropanolic extractView study →Reference 27Mahady et al. · 2008Case reportUnited States Pharmacopeia review of the black cohosh case reports of hepatotoxicityView study →}; nonetheless regulators in the EU, Australia, and Canada require a hepatotoxicity caution, so the herb should be avoided in existing liver disease, used cautiously alongside hepatotoxic drugs, and discontinued at any sign of liver dysfunction ^{27,30Reference 27Mahady et al. · 2008Case reportUnited States Pharmacopeia review of the black cohosh case reports of hepatotoxicityView study →Reference 30Le et al. · 2025ReviewReview of black cohosh-induced toxicity and adverse clinical effectsView study →}. A 2025 toxicology review also reports an aneugenic genotoxicity signal for black cohosh extract in vitro, a newer concern still being characterised ^{30Reference 30Le et al. · 2025ReviewReview of black cohosh-induced toxicity and adverse clinical effectsView study →}. Because its mechanism is non-classically estrogenic and controlled trials have not shown stimulation of breast or endometrial tissue, it is often considered usable in hormone-sensitive settings, but this remains an area of caution rather than established safety ^{4Reference 4Castelo-Branco et al. · 2021Meta-analysisReview & meta-analysis: isopropanolic black cohosh extract iCR for menopausal symptoms — an updateView study →}.

Scope note: formal herb–drug interaction studies are lacking. Co-use with hepatotoxic medications is cautioned on mechanistic and case-report grounds, and in-vitro CYP signals exist, but no robust clinical interaction data are available — treat interactions as not adequately assessed rather than absent.