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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16 thoughts on “Black Cohosh and Hot Flashes

  1. windriven says:

    “In their “at a glance” summary they characterize the scientific evidence as “mixed.”

    NCCAM, you see, believes in grading on a curve. In the world of quackery the anecdotal evidence that “this guy I know has an aunt who says …” gets partial credit. If the herb in question isn’t a schedule 1 narcotic and doesn’t immediately cause cancer of the toenails, it gets extra credit. There is, of course, the loss of a few points because “scientific” evidence is entirely negative. So the final grade is ‘mixed’, we’ll call that a B.

  2. AllieP says:

    This in keeping with my experience. My lactation consultant put me on fenugreek tablets to increase my milk supply, but the only place where I could find any information on its effacacy was lactation echo chamber websites — the NIH says that the science is not there. I took the tablets for a few weeks and noted neither the “smell of maple syrup” which was supposed to permeate my body to show that it was working, nor any notable increase in milk supply. I did note a phenomenal increase in gas, in both me and my baby.

    What I didn’t know then (and know now) is that when LCs recommend “herbal supplements, even if they are RNs, look up the science.

  3. gfb1 says:

    I have a vague recollection of an early study with black cohosh that was showing highly significant effects in alleviating ‘hot flashes’. Upon analysis of the black cohosh supplements — which were not produced in the US — a significant amount of DDT contaminating the supplements was measured.
    Accounting, of course, for the estrogenic effect …

    yikes. just realized that I posted a similar comment in previous blogposts ..

    btw; at least one “real” reference regarding contamination of botanicals with insecticides (and other fun compounds) can be found here:

    at least, I’m consistent (and a longtime reader… )

  4. cervantes says:

    This is an excellent example of the paradoxical nature of NCCAM. They funded a legitimately designed trial. It had, as do all of their trials, negative results.

    So the public has been served! A useless nostrum debunked! Sadly, no. The evidence was indeed produced, yet it is obfuscated, buried, ignored. They won’t just come out and say, “We paid a big chunk of your money to test it, and it doesn’t work. You’re welcome.” If they would do that, we might go easier on them.

  5. Jan Willem Nienhuys says:

    In this context it must be mentioned that block cohosh (Cimicifuga racemosa – wouldn’t it be a great idea to always provide the official scientific name for any kind of herb?) is dangerous too:

    See the statement of the European Medicines Agency, also from 2006:

    EMEA Public Statement on herbal medicinal products containing cimicifugae racemosae rhizoma – Serious hepatic reactions

  6. Harriet Hall says:

    The Natural Medicines Comprehensive Database rates it as only “possibly effective” (lower than their “likely effective” and “effective” ratings) and recently downgraded its safety rating from “likely safe” to only “possibly safe.”

  7. Badly Shaved Monkey says:

    The Natural Medicines Comprehensive Database rates it as only “possibly effective” (lower than their “likely effective” and “effective” ratings) and recently downgraded its safety rating from “likely safe” to only “possibly safe.”

    I find that quite funny.

    Evidence of efficacy DOWN
    Evidence of toxicity UP.

    Basically, that makes it the opposite of a real medicine.

  8. Thanks, Harriet. I was trying to think of other commonly used databases to check. But also – I looked at the articles that came up on Google, which are the ones people will see if they search on hot flashes.

    The others I found were pretty similar:

    Univ. of Maryland:

    Overview states that “it is used”

    If you read deep you get to the negative evidence, but a very squirrely treatment of the evidence – saying – but it still works, more research is needed, etc.

  9. daijiyobu says:

    Something of note regarding naturopaths and their supplements:

    unlike physicians, naturopaths also have distribution agreements with supplement companies and ‘alternative’ labs that recommend the supplements after testing.

    Often, the patient is then channeled into buying directly from that distributor with the naturopath getting a cut [almost like multi-level marketing].

    In that light, NDs / NMDs have a dual committment to therapies like BC:

    first, it fits their ideology that herbs though HARDLY TESTED are a parallel / as equal AND EVEN BETTER route than well-vetted pharmaceuticals which have shown safety and efficacy;

    second, half their incomes come from their dispenaries.


  10. tmac57 says:

    A proposal for an effective SBM blogpost title:

    “Worthless and Dangerous Supplements Your Alt-Med Provider Doesn’t Want You To Know About!!!”

    (You’re welcome.)

  11. nybgrus says:

    One of my pharmacist friends was talking about black cohosh recently – she said that there were studies showing it was linked to liver damage and failure. So lets see – no evidence it works particularly well, if at all, plus admittedly increased toxicity and at least a chance of liver damage/failure… if you told these alties that it was a pill from GSK or Merck instead of a ground up plant from “Hippie Flower Shop” they’d call you an evil BigPharma schill and never dream of taking it.

    Boggles the mind, really.

  12. norrisL says:

    And once again, for those who believe that all things natural are good, let me point out that Taipan venom is natural. The Inland Taipan of Australia is THE most deadly snake in the world in terms of how many mice it can kill per bite. And it’s all natural.
    Castor oil plant produces ricin, one of the most deadly toxins to be found. Natural. Blue green algae, quite lethal. And natural.

  13. norrisL – I like to use poison ivy as an example myself. It’s particularly useful when someone’s trying to sell you on the idea that all natural cosmetics must be hypo-allergenic.

  14. Jann Bellamy says:

    NCCAM’s notes on the safety of black cohosh are irresponsible. The website says:

    “women should discontinue use of black cohosh and consult a health care practitioner if they have a liver disorder or develop symptoms of liver trouble”

    When actually, according to the Natural Medicines database:

    “The United States Pharmacopeia also recommends cautionary labeling on black cohosh products. . . Until more is known about this potential risk, consider monitoring liver function in patients who take black cohosh.”

    In other words, women should know about this risk BEFORE they take black cohosh and perhaps should be monitored, not wait until actual liver damage may have occurred.

    NCCAM also advises:

    “It is not clear if black cohosh is safe for women who have had hormone-sensitive conditions such as breast cancer or for pregnant women or nursing mothers.”

    In fact, it is clear, again from Natural Medicines:

    “black cohosh does seem to increase metastatic cancer in animals with existing cancer. . .Therefore, black cohosh shouldn’t be used by women with existing breast cancer or women with a high risk of developing breast cancer.”
    Natural Medicines also recommends against use by pregnant women or nursing mothers.

    NCCAM says the risk of drug interactions is “small.” Wrong again.

    Natural Medicines: Patients taking hepatotoxic drugs (e.g., Tylenol) or should NOT take black cohosh, nor should patients receiving cisplatin chemotherapy.

  15. Calli Arcale says:

    The authors of the study listed as a limitation:

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

    When I see this, I’ve started to read this sort of thing as “they made us control for confounders, and all the evidence went away. Waaaah!”

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