Black Cohosh and Hot Flashes

Black Cohosh, an herbal “supplement” (i.e. unregulated drug) remains popular for the treatment of hot flashes and other autonomic symptoms resulting from menopause. This product is yet another good example of the double standard that the supplement industry and ideological promoters are allowed to employ.

The NCCAM website gives this summary:

Black cohosh, a member of the buttercup family, is a plant native to North America. It has a history of use for rheumatism (arthritis and muscle pain) but has been used more recently to treat hot flashes, night sweats, vaginal dryness, and other symptoms that can occur during menopause.

While the information is available if you look through the links below, their summary makes no mention of the fact that their own studies show black cohosh is ineffective. In their “at a glance” summary they characterize the scientific evidence as “mixed.”

The Natural Standard website is far worse. Although touted as a reliable source of scientific information on herbal supplements, they reveal a very biased editorial agenda. Here is their “bottom line” summary of Black Cohosh:

Black cohosh is one of the highest selling herbs in the United States and is popular as an alternative to hormonal therapy in the treatment of menopausal (climacteric) symptoms such as hot flashes, mood disturbances, diaphoresis, palpitations, and vaginal dryness (1;​2). Several controlled trials and case series have reported black cohosh to improve menopausal symptoms for up to six months. Although these initial studies are suggestive, they have been few in number and have universally suffered from methodological weaknesses.

They also state:

Since the Women’s Health Initiative Trial was halted early due to an excess risk of stroke and other adverse outcomes, millions fewer women are using prescription hormone replacement therapy. However, a 2005 survey has shown there has been no appreciable increase in alternative therapies, including black cohosh (13).

Why are they so concerned that women are not using black cohosh or other “alternative” therapies when the evidence does not support their efficacy?

Let’s take a look at the actual evidence. The best study to date is the 2006 double-blind placebo-controlled trial funded by the NCCAM. They compared Black Cohosh alone, plus with other herbs, plus with other herbs and soy, to standard hormone replacement therapy and placebo. The three herbal groups showed no significant difference from placebo, while the hormone replacement group did show significant improvement. The only exception was the soy group, which showed greater symptom intensity at 12 months. This is the best evidence to date and it was dead negative.

The authors of the study listed as a limitation:

The trial did not simulate the whole-person approach used by naturopathic physicians.

How is this a limitation? Where is the evidence that the “whole-person” approach of naturopaths has any basis in reality or provides any improvement in outcome? This is nothing but special pleading, an attempt to water down the significance of these negative results.

A 2008 systematic review of black cohosh and hot flashes concluded:

The evidence from these RCTs does not consistently demonstrate an effect of black cohosh on menopausal symptoms; a beneficial effect of black cohosh on peri-menopausal women cannot be excluded. The efficacy of black cohosh as a treatment for menopausal symptoms is uncertain and further rigorous trials seem warranted.

In other words — the evidence is negative, but we don’t want to give up yet because black cohosh is still popular. Of course, its popularity was manufactured by unfounded claims for efficacy, which have not held up under rigorous study.

It must also be noted that in the controlled trial all groups, placebo included, did show a decrease in the number of hot flashes over the year of the study. This likely reflects the natural course of symptoms (hot flashes do tend to resolve over time) and also the placebo effect in terms of noticing and reporting symptoms. The lesson from this is that any unblinded study of any treatment for menopausal hot flashes is likely to show a significant decrease in symptoms over time. This study emphasizes the virtual uselessness of unblinded studies in evaluating subjective symptoms, like hot flashes.

And yet, it is precisely these unblinded studies that proponents are using to argue that the evidence is “mixed” and that black cohosh deserves further study.

However, a more rational science-based evaluation would take into consideration the relationship between the rigor of the studies and the effect size. The most rigorous studies are negative — that is consistent with the null hypothesis — with the conclusion that black cohosh simply does not work for hot flashes.


If black cohosh were a pharmaceutical and not a supplement, I don’t think there would be much debate about its effectiveness. The data is essentially negative, which means that the only reasonable science-based recommendation is not to recommend black cohosh for hot flashes. Further study is not unreasonable, but neither it is needed.

However, the NCCAM and Natural Standard shy away from this recommendation. Natural Standard doesn’t even mention the negative evidence in their bottom line summary, but rather decry the fact that more women are not using black cohosh or other supplements. NCCAM resorts to their typical weasel statement that black cohosh “has a history of use” or “has been used for.”

For proponents, when it comes to supplements (or any so-called “alternative” modality), no evidence for lack of efficacy ever seems to be adequate.

Posted in: Herbs & Supplements

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