Black Cohosh

What the Pooled Evidence Says

The Cochrane review is the honest starting point, because it is the largest attempt to add up everything at once. Sixteen randomised trials, 2,027 perimenopausal and postmenopausal women, oral monopreparations at a median of 40 mg/day for a mean of 23 weeks.

The result for hot-flush frequency: a mean difference of 0.07 flushes per day versus placebo (95% CI −0.43 to 0.56, P = 0.79). For overall menopausal symptom scores: SMD −0.10 (95% CI −0.32 to 0.11, P = 0.34). Hormone therapy, by contrast, significantly beat black cohosh on both counts.

The authors' conclusion — "insufficient evidence to support the use of black cohosh for menopausal symptoms" — has not been overturned since.

The single best-designed American trial reached the same place independently. The HALT trial randomised 351 women aged 45–55 with two or more vasomotor symptoms per day to black cohosh 160 mg/day, a multibotanical, a multibotanical plus soy counselling, conjugated equine oestrogen, or placebo, and followed them for a year. No herbal arm differed from placebo at 3, 6 or 12 months. One arm did differ: at 12 months, symptom intensity was significantly worse with multibotanical-plus-soy than with placebo (P = 0.016).

Why Some Trials Are Positive Anyway

The contradiction is not noise; it is chemistry. Trials do not test "black cohosh," they test a specific extract.

The isopropanolic extract (iCR, marketed as Remifemin) has its own trial base, and some of it is positive — a multicentre randomised trial in Obstetrics and Gynecology reported efficacy and safety for climacteric symptoms with the isopropanolic preparation. Ethanolic extracts and unstandardised root powder are different products with different triterpene profiles, and pooling them is part of why the meta-analytic signal collapses.

If you are going to take black cohosh at all, taking the extract that was actually studied is the minimum bar.

The Mechanism Is Not What the Label Implies

For thirty years black cohosh was sold as a plant oestrogen. It is not one.

HALT measured vaginal cytology, endometrial thickness and reproductive hormones and found nothing moved. What has been found is in vitro serotonergic activity, with N-omega-methylserotonin identified as a plausible active constituent.

That is a genuinely useful reframe. It puts black cohosh in the same conceptual family as the SSRIs and SNRIs that guidelines do recommend for vasomotor symptoms — while noting the obvious: the pharmaceutical version of that mechanism has Level I evidence behind it and this one does not.

The Liver Question

This is the part that separates black cohosh from the merely ineffective.

Case reports of cholestatic drug-induced liver injury exist, and the European Medicines Agency requires a liver-reaction warning on black cohosh products. A quantitative causality evaluation of nine suspected cases found the attribution frequently weaker than the headlines implied, and a meta-analysis of five randomised trials in 1,117 women treated with iCR for 3–6 months found no effect on AST or ALT (overall fixed effect 0.055 ± 0.062 for AST, 0.063 ± 0.062 for ALT).

The reasonable synthesis: this is idiosyncratic and rare, not dose-dependent and common. Controlled trials will not detect a one-in-many-thousands reaction, and their reassurance should not be mistaken for its absence.

Practical consequence: check liver enzymes at baseline and around three months, and stop at the first sign of jaundice, dark urine, right upper quadrant pain, or unexplained fatigue.

Where This Leaves It

The North American Menopause Society's 2023 nonhormone therapy position statement does not recommend supplements or herbal remedies for vasomotor symptoms. Black cohosh is inside that judgment.

A defensible use case still exists: a woman who cannot take hormone therapy, has declined or failed the Level I non-hormonal options, wants to try one botanical, and accepts that the expected effect is small and may be entirely placebo. For her, the isopropanolic extract at 40 mg/day for three to six months with liver monitoring is a reasonable, low-cost experiment — provided nobody pretends it is an HRT substitute.

Related Research

• Perimenopause Supplements: What the Evidence Actually Supports
• The Menopause Transition Protocol
• Soy Isoflavones