Behind the Headlines

Wednesday January 14 2009

Red clover showed no evidence that it reduces menopausal hot flushes

The Daily Mail reported today that herbal remedies to treat menopausal symptoms are unproven and could actually damage health. The newspaper said that an independent review by experts has found no strong evidence that herbal remedies such as ginseng, black cohosh and red clover have any effect on the hot flushes, sleeplessness and loss of libido associated with menopause. It said that more menopausal women have turned to using herbal remedies following recent HRT health scares, but their safety is untested, and there is limited information on how they interact with other medicines.

The authors of this review examined the evidence for the safety and efficacy of a number of commonly used herbal remedies for menopausal symptoms. They found that the only treatment that seemed to have any evidence of an effect was black cohosh, which can potentially cause liver toxicity. However, even these results were mixed. In general, the researchers found that this area of study is under-researched and under-reported. The public should be aware that most herbal medicines do not have to comply with the stringent safety, quality and manufacturing regulations that govern conventional medicines. The majority are unlicensed for the treatment of medical conditions.

Where did the story come from?

This is a narrative review reported in the Drug and Therapeutic Bulletin (DTB) of the British Medical Journal. Individual authors of the piece are not listed. The DTB reports that it is independent of the pharmaceutical industry, government and regulatory authorities, advertising, and other commercial sponsorship.

The journal website reports that most articles for DTB are written by outside experts commissioned by the editorial team. The draft article undergoes “detailed scrutiny, collaboration and revision, involving a wide range of commentators and several editing stages”, and the final article is “no longer attributable to any one source, is published unsigned, and represents the view of DTB”.

What kind of scientific study was this?

This narrative review aimed to review the efficacy and safety of alternative therapies for the menopause. Many women are said to now use herbal remedies for the relief of menopausal symptoms (one survey suggesting 40%). This has been attributed to concerns over links between hormone replacement therapy (HRT) and an increased risk of breast cancer, ovarian cancer and thromboembolism. The herbal remedies discussed are black cohosh, red clover, evening primrose oil and ginseng.

What were the results of the study?

The authors say that there are only a few available studies on the efficacy of herbal remedies, and they often have numerous methodological limitations. Findings for individual remedies are discussed below:

Black cohosh

Black cohosh – the root and rhizome of the plant – is widely used for menopausal symptoms, but the authors say it is not clear how it is supposed to work.

The authors report that three trials comparing black cohosh to placebo (and one that compared it to conjugated oestrogen or placebo) found the herbal remedy to have no significant benefit on menopausal symptoms. Three other trials found it to be beneficial: two of these found that it gave a similar reduction in symptoms to conventional menopausal medications; one placebo-controlled trial found a greater improvement with black cohosh than with placebo. Two trials comparing a mix of black cohosh and St John’s wort with placebo found that the herbal mix was more effective at reducing menopausal symptoms.

Safety data is said to be limited, but suggests that black cohosh and the placebo have similar profiles of adverse effects. However, black cohosh carries risks of headaches, dizziness, gastrointestinal disturbances and possibly liver toxicity.

Red clover

Red clover contains phytoestrogens, which act similarly to oestrogen and are also found in soy foods.

A systematic review of products containing phytoestrogen has previously been carried out, involving 30 randomised trials and 2,730 subjects. This included seven trials of red clover extract, five of which had their results combined in meta-analysis. This showed no benefit of red clover over placebo in reducing symptoms of hot flush. However, many of the trials were said to be underpowered, and some trials had high numbers of participants who dropped out.

This review found that using phytoestrogens had no increase in adverse effects, and appeared to be well-tolerated in most long-term studies. However, its safety in women with hormone-sensitive cancers (cancers that may be exacerbated by oestrogen and similar compounds) is uncertain.

Dong quai

Dong quai is a traditional Chinese medicine that is used for various conditions, including menopause. One placebo-controlled randomised controlled trial found that it did not significantly improve symptoms compared with placebo. Another placebo-controlled randomised controlled trial of a dong quai-and-chamomile combination found it to be significantly more effective than placebo in reducing hot flushes.

Dong quai has been associated with photosensitivity and, importantly, it interacts with warfarin.

Evening primrose oil

It is uncertain how evening primrose oil affects menopausal symptoms. One placebo-controlled randomised controlled trial including 56 women found that evening primrose oil did not reduce the frequency of hot flushes any more than placebo.

Evening primrose oil can further increase the risk of such events when given in combination with drugs that increase the propensity to seizures (e.g. phenothiazines).

Ginseng root

Two randomised controlled trials of ginseng root compared with placebo found that it did not alleviate mood, cognition or well-being in post-menopausal women. Ginseng has been associated with adverse effects of headache, sleep disturbance and gastrointestinal disorders. It may possibly interact with warfarin as well. There are a number of different preparations grouped under the general term ‘ginseng’, so caution is needed when selecting products.

Other herbal preparations

The authors say that other herbal preparations with limited evidence of effect for menopausal symptoms are wild yam, chaste tree, hops and sage leaf. Kava kava was previously used for anxiety but has been banned due to reports of liver damage.

What interpretations did the researchers draw from these results?

The authors conclude that the use of herbal medicines to treat menopausal symptoms is widespread, but there is a lack of licensed products available on the market. They say the efficacy and safety of herbal medicinal products is generally under-researched, and there is limited information on potential herb-drug interactions.

They say the results for the efficacy of black cohosh are mixed (although the potential for liver toxicity should be noted). There is no convincing evidence for red clover, and little evidence for or against other commonly used herbs for menopausal symptoms.

What does the NHS Knowledge Service make of this study?

The conclusions of this narrative review seem reasonable on the basis of the studies it described. However, it is unclear if the review used systematic methods to identify all relevant trials on herbal remedies and menopausal symptoms. Additionally, insufficient information was given about the methods used in the studies to allow an in-depth analysis of their quality, although many were described as having limitations.

The public should be aware that most herbal medicines do not have to comply with the stringent safety, quality and manufacturing regulations that govern conventional medicines. The majority of herbal medicines are unlicensed for the treatment of medical conditions. Herbal medicines may also affect how other medications work when taken together.

The UK Medicines and Healthcare products Regulatory Agency (MHRA) is reportedly implementing the Traditional Herbal Medicinal Products Directive, which will become operational in 2011. This will mean that all over-the-counter herbal remedies will have to conform to the Traditional Herbal Medicines Registration Scheme, and meet safety and quality standards.

For now, the narrative review’s suggestion that healthcare professionals should routinely ask women with menopausal symptoms if they are using such herbal remedies, seems a reasonable one.

Links to the headlines

Now women are warned herbal remedies for the menopause 'could damage health'. Daily Mail, January 14 2009

Herbal menopause cures lack proof. BBC online, January 14 2009

Little evidence herbal menopause remedies work. The Daily Telegraph, January 14 2009

Links to the science

Herbal medicines for menopausal symptoms. Drug and Therapeutics Bulletin 2009; 47: 2-6

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Edited by NHS Choices