Black Cohosh for Hot Flashes

Black cohosh is one of the most widely used herbs for hot flashes, and the honest answer is that it probably doesn't do much. In a year-long trial of 351 women, hot flashes were no less frequent on 160 mg a day than on placebo, while hormone therapy cut about four more a day than placebo (Newton 2006). In a 2012 Cochrane review, the three trials that measured daily hot flash frequency found no significant difference from placebo (Leach 2012).

Why the verdict is mixed rather than negative: a 2026 review for the International Menopause Society rated the evidence for black cohosh as moderate certainty (Maunder 2026), and the clearest positive trial tested one specific isopropanolic extract (Osmers 2005), so a small effect from some products can't be ruled out. The Menopause Society's 2023 statement recommends hormone therapy or proven non-hormonal treatments instead and does not recommend herbal supplements (NAMS 2023). If you are weighing related symptoms, see black cohosh for night sweats and black cohosh for menopause.

Black cohosh is often assumed to work like estrogen, but the evidence says otherwise. In ovariectomised rats, an isopropanolic extract had no estrogenic or antiestrogenic effect on the uterus or vagina; in lab tests the same extract bound strongly to serotonin receptors (5-HT1A, 5-HT1D and 5-HT7), and a methanol extract acted as a partial agonist at the 5-HT7 receptor, which is linked to the brain's temperature control (Burdette 2003). Extracts also activate the mu opiate receptor in cells (Rhyu 2006).

A serotonin route would fit with the fact that some antidepressants reduce hot flashes, which is why researchers have proposed it for black cohosh (Hajirahimkhan 2013). In women, 17 trials found no significant impact on circulating hormone levels or on estrogen-responsive tissue such as breast (Fritz 2014).

All of the receptor findings come from cells and animals. They don't show that the amount in a supplement reaches those receptors in people, and the active compounds in black cohosh still aren't known (NIH ODS). A plausible mechanism also can't outweigh what happened in the trials, where women on placebo often improved as much as, or more than, women on black cohosh (Pockaj 2006; Geller 2009).

Doses in trials varied widely. The Cochrane review's trials used a median of 40 mg a day for an average of 23 weeks (Leach 2012). The one large clearly positive trial gave isopropanolic extract tablets corresponding to 40 mg of herbal drug (root) a day for 12 weeks (Osmers 2005). Trials of other, ethanolic extracts were no better than placebo: 160 mg a day for a year (Newton 2006) and 128 mg a day for a year (Geller 2009; dose from NIH ODS). Because these are different extracts, they don't show whether a higher dose of any one product works better; a meta-analysis of the isopropanolic extract reported larger effects at higher doses (Castelo-Branco 2021). A crossover trial using 20 mg twice a day was also negative (Pockaj 2006).

Products differ in how the root is extracted and standardised; many are standardised to at least 1 mg of triterpene glycosides a day (NIH ODS). Because the compounds responsible for any effect are unknown, a milligram figure on one label isn't equivalent to the same figure on another. Timing relative to meals wasn't tested.

The 2012 Cochrane review included 16 randomised trials in 2,027 perimenopausal and postmenopausal women. In the three trials that measured it (393 women), black cohosh made no difference to daily hot flash frequency compared with placebo (mean difference 0.07 flushes a day, 95% CI -0.43 to 0.56, P = 0.79), and hormone therapy did better than black cohosh. The reviewers rated trial quality as generally unclear and concluded there was insufficient evidence to support black cohosh for menopausal symptoms (Leach 2012).

Three NIH-funded trials, including the largest, were negative. In 351 women aged 45-55, black cohosh 160 mg a day didn't differ from placebo at 3, 6 or 12 months, with differences under one symptom a day (Newton 2006). In a 12-month trial of 89 women, vasomotor symptoms fell 34% on black cohosh, 63% on placebo and 94% on hormone therapy, and only hormone therapy beat placebo (Geller 2009). In a crossover trial of 132 women, hot flash frequency fell 17% on black cohosh and 26% on placebo (P = .36) (Pockaj 2006).

Some pooled analyses do find a benefit. A 2023 meta-analysis of 22 studies (2,310 women) found black cohosh improved hot flashes compared with placebo (Hedges' g 0.315, 95% CI 0.107 to 0.524, P = 0.003), a small effect; it pooled black cohosh alone and combined with other ingredients (Sadahiro 2023). The NICE guideline's network meta-analysis of 47 trials found black cohosh and isoflavones more effective than placebo, though not significantly better than estrogen plus progestogen, which ranked most effective overall (Sarri 2017). A 2026 systematic review for the International Menopause Society rated the evidence for black cohosh in vasomotor symptoms as moderate certainty, while calling the overall evidence limited (Maunder 2026).

Much of the positive signal comes from one isopropanolic extract. A meta-analysis focused on it reported a moderate effect on menopausal symptom scores (SMD -0.694) and efficacy comparable to low-dose transdermal estradiol (Castelo-Branco 2021). Its key trial, in 304 women, beat placebo on a menopause symptom scale over 12 weeks, with the hot flush subscore the most responsive measure and women early in the menopause transition benefiting most (Osmers 2005).

In a 12-week trial of 122 women with at least three hot flashes a day, an ethanolic extract failed its primary analysis; only women with more severe symptoms improved more than on placebo (47% versus 21% on the Kupperman Index), and the hot flash score result was borderline (P less than 0.052) (Frei-Kleiner 2005). That is a subgroup finding and needs confirming.

In women treated for breast cancer, an 85-woman placebo-controlled trial found no significant difference in hot flash number or intensity (Jacobson 2001), and a systematic review concluded there is a lack of evidence that black cohosh reduces hot flashes in breast cancer patients (Fritz 2014). Missing from the evidence: better-reported trials, since the Cochrane reviewers could not judge most trials' quality (Leach 2012), and full descriptions of the preparations used, so results can be matched to products (NIH ODS).

In trials, black cohosh was generally well tolerated: dropout rates matched placebo (Sadahiro 2023), and side effects such as stomach upset and rash were usually mild and passing (NIH ODS). Most studies lasted six months or less, and its long-term safety hasn't been studied (NIH ODS).

The concern is the liver. At least 83 cases of liver damage, including hepatitis and liver failure, have been reported with black cohosh worldwide; a causal link hasn't been established, and some products may have been contaminated or contained the wrong species (NIH ODS). A pooled analysis of five trials of an isopropanolic extract (1,117 women, 3-6 months) found no significant change in liver enzymes (Naser 2011). The US Pharmacopeia advises people with liver disorders to avoid it and anyone who develops symptoms of liver trouble to stop (NIH ODS). In breast tissue, a systematic review found no link to increased breast cancer risk (Fritz 2014).

No clinically relevant drug interactions are known, although this hasn't been studied systematically (NIH ODS). In healthy volunteers, 28 days of black cohosh weakly inhibited the liver enzyme CYP2D6 by about 7%, which the researchers judged unlikely to be clinically relevant, though they noted it may still interact with drugs cleared by CYP2D6 (Gurley 2005), and 80 mg a day for 14 days had no effect on CYP3A, the enzyme that clears many common drugs (Gurley 2006).

Given the reported liver injuries, take extra care when combining it with other medicines or supplements that can affect the liver. If you are on tamoxifen or another cancer treatment, ask your oncologist before adding any herbal product.