Evening Primrose Oil for Premenstrual and Menopausal Symptoms
By Dónal P. O'Mathúna, PhD Lecturer in Health Care Ethics, School of Nursing, Dublin City University, Ireland. Dr. O'Mathúna reports no consultant, stockholder, speaker's bureau, research, or other financial relationships with companies having ties to this field of study.
Complementary and alternative medicine (cam) continues to be a common way for women to treat symptoms of premenstrual syndrome (PMS) and menopause. In one national survey, 43% of women ages 45-57 years used CAM.1 Those with menopausal symptoms were almost twice as likely to use CAM, with herbal remedies being the most frequently used CAM approach to treating menopausal symptoms. Evening primrose oil is an herbal remedy commonly used to treat menopausal symptoms and PMS.
Evening primrose oil is obtained from the seeds of a North American wildflower (Oenothera biennis).2 Early English settlers brought the flower back to England where it was cultivated for its nut-flavored root. The oil also was extracted from the seeds and became known as the King's Cure-All. Surveys have found that it was still a very commonly used herbal medicine in England. Two evening primrose oil products were licensed by Britain's Medicines Control Agency. The products were available by prescription to treat atopic eczema and mastalgia (breast pain). However, in 2002 the licenses were revoked after the evidence available for its effectiveness was reviewed.3
Nonetheless, the use of evening primrose oil to treat menopausal symptoms has become more popular since problems were reported in 2001-2002 with hormone replacement therapy. Evening primrose oil contains a high proportion of essential fatty acids. The two most common types present in the oil are linoleic acid (about 65%) and gamma-linolenic acid (GLA, 8-10%).4 Evening primrose oil is valued primarily for its GLA. It is one of the richest plant sources of GLA, with only borage oil (24%) and black currant seed oil (16%) containing more GLA. GLA is converted into a number of anti-inflammatory prostaglandins in the body, which is why evening primrose oil also is recommended to treat numerous chronic inflammatory diseases.
Mechanism of Action
How evening primrose oil might treat premenstrual or menopausal symptoms is not clear. There is some preliminary evidence that women with premenstrual syndrome have lower than normal levels of GLA.4 Epidemiological studies have shown a connection between low dietary levels of GLA and a number of illnesses. However, a precise mechanism of action for evening primrose oil is not known.
Very few high-quality studies have been conducted using evening primrose oil for specific conditions in humans. Only one controlled study of evening primrose oil to treat menopausal symptoms was found. This 1994 study examined the impact of evening primrose oil on hot flashes and night sweats.5 Fifty-six women with menopausal symptoms were randomized to receive either evening primrose oil (4 g/d plus 80 mg/d vitamin E) or placebo capsules for six months. Only 35 women finished the study. Although all women showed some improvements, the researchers concluded that evening primrose oil offered no benefit over placebo. An extensive review of herbal remedies used for menopausal symptoms and published at the end of 2005 failed to uncover any subsequent trials of evening primrose oil.6
Evening primrose oil has been one of the more popular natural therapies for PMS. A small number of open studies found some benefits from evening primrose oil. However, when studied in randomized controlled trials, evening primrose oil was found to be no more beneficial than placebo. For example, 38 women with PMS were randomly assigned to receive either 4 g/d evening primrose oil or placebo.7 The women took the capsules for three menstrual cycles and then crossed over to the alternative group for three more cycles. Ten PMS and menstrual symptoms were measured. All subjects in both groups showed improvements in all 10 symptoms, and in an overall PMS score, but no significant differences were found between the two groups. Another randomized controlled trial used 38 women with PMS, but administered 6 g/d evening primrose oil.8 Again, no significant differences were found between the two groups.
Two systematic reviews of research on evening primrose oil for PMS have been carried out. One in 1996 was unable to carry out a meta-analysis due to differences in the study designs.9 The authors reported that the two trials described above were the only high-quality studies. A 2001 review discussed these two trials and two other placebo-controlled trials, which also found evening primrose oil no better than placebo.10 PMS is a condition that has been found to be highly responsive to placebos, with up to 80% of subjects responding well to placebos.7
Anecdotal reports claim that evening primrose oil is particularly effective in reducing breast pain (mastalgia), including that associated with PMS. One of the largest studies ever conducted on mastalgia investigated this claim.3 A total of 555 women were randomized to one of four groups. Each woman took 4 g/d of capsules containing either evening primrose oil alone, evening primrose oil plus multivitamins, multivitamins alone, or placebo. After four months of blinded treatment, all groups showed an average 35% reduction in breast pain. No statistically significant differences were found between any of the four groups. The trial continued for another six months with all subjects receiving evening primrose oil, either with or without multivitamins. This phase was an open trial, with breast pain being reduced by another 50%, but with no differences between the two groups. The researchers concluded that evening primrose oil was not superior to placebo in treating mastalgia.
The most commonly reported adverse effects of evening primrose oil in clinical trials are gastrointestinal. These are usually mild to moderate, with nausea being the most common. The effects of long-term use have not been examined. It should be noted that the withdrawal of evening primrose oil's medical license in Britain was not because of concerns about safety, but for lack of evidence of effectiveness. Evening primrose oil may be associated with pregnancy complications and, therefore, should not be used by pregnant women.11 However, it is considered safe in children and lactating women.
Most studies have used four 500 mg capsules taken twice daily (a total of 4 g/d evening primrose oil). Recommendations range from 2-6 g/d.
A relatively small number of studies have examined the effectiveness of evening primrose oil in treating PMS and menopausal symptoms. The controlled studies reveal a consistent pattern of similar effectiveness as placebo. Such symptoms are known to respond well to placebo effects, which may explain why evening primrose oil has gained a reputation for effectiveness. Such findings point to the importance of addressing symptoms of PMS and menopause holistically.
In spite of its popularity, evening primrose oil does not appear to be any more beneficial than placebo in treating menopausal or PMS symptoms. Some women may have very low levels of GLA in their diet, or may not produce adequate amounts within their bodies. They may receive some general health benefits from supplementing their diet with evening primrose oil. However, its usefulness in treating any particular condition associated with PMS or menopause is not supported by clinical research.
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