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Black cohosh and cancer

Black cohosh is a herb. It belongs to the same plant family as the buttercup and grows in North America (the USA and Canada). It is also called black snakeroot, macrotys, bugbane, bugwort, rattleroot, rattleweed, rattlesnake root or squawroot.  

Its scientific names are

  • Actaea racemosa
  • Cimicifuga racemosa

Available scientific evidence does not support claims that black cohosh is effective in treating or preventing cancer.

You can buy black cohosh as a dietary supplement in health food shops and online. Manufacturers say that it can help to reduce the cramps and discomfort women may have just before and during a period. Many women also use it to help with the symptoms and side effects of menopause, such as hot flushes. Some researchers say that it seems to have oestrogen like effects on the body.

Some women with breast cancer use black cohosh because they believe it will help to control symptoms of menopause caused by their cancer treatment. There isn’t enough scientific evidence to prove this. And we can’t be completely sure it’s safe to take black cohosh after breast cancer treatment.

Some people claim that taking black cohosh may help treat cancer or reduce your risk of getting breast cancer or prostate cancer. There is not enough scientific evidence to support this. We need more research to find out if it works, and if it is safe to take.

If you are interested in using black cohosh or any other type of complementary or alternative medicine, always talk to your doctor first. We recommend that you don't replace your conventional cancer treatment with any type of unproven therapy such as black cohosh.


How you take black cohosh

Black cohosh comes as

  • Capsules
  • Tablets
  • A powder
  • Liquid
  • Tincture

There is no standard dosage for black cohosh. A common German brand called Remifemin is used as a menopausal remedy. The suggested dose for this concentrated extract is between 15 and 30mg a day.

Other types of black cohosh may recommend that you take as much as 200mg a day.


Side effects of black cohosh

Side effects are rare with small to moderate amounts of black cohosh. Most studies have used black cohosh for less than 6 months and so the long term effects are not known. We need more research to find out exactly what the long term effects are and if it is safe to take.

The most common side effects are stomach pain, feeling or being sick, or skin rashes. But very high doses (above 100mg) can cause

  • A slowing of your heart rate
  • Lowering of blood pressure
  • Headaches
  • Dizziness and light headedness
  • Womb (uterine) contractions
  • Joint pain

There have been a few reports of black cohosh seriously damaging the liver. Although it is not clear whether black cohosh was responsible for liver damage in these reports, the Medicines and Healthcare products Regulatory Agency (MHRA) say that all black cohosh products should carry a warning label.

Doctors are worried that using black cohosh long term may cause thickening of the womb lining. This could lead to an increased risk of womb cancer. One study found that there was no thickening of the womb in women using black cohosh for 3 months. 

Some research suggests that black cohosh can interfere with how some cancer drugs work, such as chemotherapy or hormone therapy but a review of studies in 2008 found the risk to be very small.


Research into black cohosh

Several published clinical trials have looked at the safety of black cohosh and how well it works. Many of the trials weren’t controlled trials and were small. Trials have looked at black cohosh in the following situations. 

Controlling menopausal symptoms for women in general

Most trials have used the German brand of black cohosh called Remifemin. Some early clinical trials showed that Remifemin helped to relieve menopausal symptoms and others showed that it didn't.

A systematic review in 2005 found that black cohosh did appear to ease menopausal symptoms. Another review in 2008 looked at all the randomised controlled trials of black cohosh in women past their menopause women and found that in some trials it seemed to work and in others it didn't. They suggest that research is carried out to see whether it may work better for women at the beginning of their menopause. Currently there is no standard preparation of black cohosh and so the variation in trials may be due to the differences in the type of black cohosh used in the studies.

A 2012 Swiss review looked at 16 studies, involving 2027 women, and also found there wasn't enough evidence to support the use of black cohosh for menopausal symptoms. The reviewers recommended more research to find the effects of black cohosh on quality of life for menopausal women, their bone health and night sweats. 

Controlling menopausal symptoms caused by breast cancer treatment

We don’t know whether black cohosh is safe to take if you have, or have had, breast cancer. It may affect the body in a similar way to the hormone oestrogen. If it does, this might trigger breast cancer cells to grow, especially in women with oestrogen receptor positive breast cancer. The latest research suggests that black cohosh doesn’t cause oestrogen like activity and behaves more like nerve signal transmitters, but we don’t know this for sure yet.

Studies looking at black cohosh for menopausal symptoms in women with breast cancer have had contradictory results. Some show a benefit and others don’t. A systematic review in 2002 found that black cohosh didn’t reduce hot flushes. A more recent study in 2003 looked at giving it to women who were taking the hormone therapy tamoxifen. This showed that it may reduce hot flushes. 

A study in Canada in 2007 reviewed 5 clinical trials. They found that black cohosh seems to be safe for women with breast cancer, as long as they don’t have liver problems. A recent study in 2012 found that black cohosh taken for 6 months by women having tamoxifen treatment reduced the number and severity of hot flushes. 

Results of studies are difficult to interpret because different amounts of black cohosh from different sources were used and they had different aims. Research is continuing so that we can find out if black cohosh is really a safe and helpful treatment for women with breast cancer. 

Some laboratory studies have found that some of the active ingredients in black cohosh could interfere with how the hormonal therapy tamoxifen is processed in the body. But these studies were done on mice, so it is difficult to know whether this risk applies to women on tamoxifen who take black cohosh.

Preventing or treating cancer

Some people have claimed that black cohosh may reduce your risk of getting breast cancer or prostate cancer. There is no evidence to prove this at the moment.

An American study published in 2007 compared women who had taken black cohosh with women who hadn’t. They found that the women who had taken black cohosh were less likely to develop breast cancer. But this is only one study. We need more research before we will know if it can help to prevent breast cancer. Another study in 2007 found that women who took black cohosh had a slightly increased time before their cancer came back compared to women who did not take black cohosh, but again this is a very small study. 

One study in mice in 2008 found that breast cancer was more likely to spread to the lung when the mice were given black cohosh. So black cohosh may have a harmful effect on areas of the body other than the breast.

Researchers are looking at the effects of black cohosh on prostate cancer cells in the laboratory and in animal studies. These are very early studies. Even if the results are positive, we will need more research before we can tell whether black cohosh can prevent prostate cancer.


Who shouldn’t take black cohosh

Some doctors recommend that you shouldn’t take black cohosh for more than 6 months at a time. People who have liver problems should not take it because it can damage the liver. You also shouldn’t take black cohosh if you

  • Have breast cancer
  • Are having some types of chemotherapy such as cisplatin – studies show that certain drugs may not work as well if you take black cohosh
  • Have blood pressure problems or take medicines for your blood pressure
  • Are pregnant or breast feeding

If you are thinking about taking black cohosh instead of hormone replacement therapy (HRT) always talk to your doctor first. Black cohosh may not be safe or suitable for you to take.

Black cohosh may also interact with drugs to treat blood pressure disorders or liver disease.


The cost of black cohosh

You can buy black cohosh remedies

  • In health food shops
  • From registered practitioners of Western herbal medicine.
  • In pharmacies
  • In supermarkets
  • Over the internet

There are many black cohosh products. Prices vary depending on where you buy it and the dosage. The amount of black cohosh in each product can vary. Our advice is to be cautious.


Things to consider

You will of course make your own decision about taking any alternative or complementary therapy. We recommend that you always check with your doctor before you start using any of them. That way, your doctor will always have the full picture about your care and treatment.

Our message is

  • Be careful
  • Check prices and the amounts each preparation contains
  • Make sure you look at all the information available
  • Talk to your cancer doctor before you buy or use any alternative or complementary therapy

We recommend that you use herbal medicine from a trained herbal medicine practitioner registered with a professional body such as the National Institute for Medical Herbalists or the College of Practitioners of Phytotherapy. The Complementary and Natural Healthcare Council (CNHC) also maintains a register that all complementary therapy practitioners can join. You can find details of these organisations below.

A herbal medicine practitioner will monitor your progress regularly and do simple liver function tests to check that there are no side effects from the prescriptions. And they also know when not to prescribe a herb. Relying on advice from staff in health food shops and the internet is very risky as the people involved in giving advice have little, or no, training.

In Europe it is important to buy only products that are registered under the Traditional Herbal Remedies (THR) scheme. Remedies that are registered under the scheme have a THR mark and symbol on the packaging. THR products have been tested for quality and safety.


Where to find more information

Our section about complementary and alternative therapies is a useful place to start for general information about complementary and alternative therapies in cancer care.

The following UK organisations give information specifically about herbal medicines.

The National Institute for Medical Herbalists
Clover House
James Court
South Street
Tel: 01392 426022

Gives information about western herbal medicine and also has a register of UK herbal medicine practitioners.

The College of Practitioners of Phytotherapy
Oak Glade
9 Hythe Close
East Sussex
BN26 6LQ
Tel: 01323 484353

Phytotherapists (phyto means plant in Greek) are herbal practitioners with specialist university training. They combine medical knowledge and skills with a scientific understanding of plant medicines. The organisation provides information and has a list of practitioners in the UK.

You can find information about black cohosh on the following websites

The Memorial Sloane Kettering Integrative Medicine website has information about many types of herbs and dietary supplements. It also evaluates alternative or unproven cancer therapies.

The CAM-CANCER website provides reliable information about complementary and alternative therapies (CAMs) for cancer.

The Complementary and Natural Healthcare Council aims to enhance public safety, by giving the general public access to a list of practitioners that have been independently assessed as meeting national standards of competence and practice.

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Updated: 27 January 2015