Visiting a garden at sun-set can provide unexpected plea-sure. As the sun goes down and most flowers close up for the night, evening primrose (Oenothera biennis) opens its four-petaled blooms, revealing colors that range from rich cream through bright yellow. Growing as tall as 8 feet, this biennial herb blooms from June through September, the flowers remaining open on cloudy and rainy days as well as at night.
In addition to its unusual nocturnal performance, evening primrose is known for its use as a remedy for discomforts ranging from bruises to premenstrual syndrome (PMS).
Down To Essentials
Evening primrose seed oil contains essential fatty acids, substances that, like vitamins, minerals, and essential amino acids, aren’t manufactured by the body but are necessary for good health. They are normally obtained through the diet. Imbalances or deficiencies in the body’s essential fatty acids have been implicated in many disorders, including asthma, migraines, inflammations, metabolic irregularities, diabetes, arthritis, and alcoholism.
The oil’s primary constituent is cis-linoleic acid, an essential fatty acid that is also commonly found in safflower, corn, cottonseed, and soybean oils. Another is alpha-linolenic acid, which is also found in canola and soybean oils, flaxseed, and leafy green vegetables. A third essential fatty acid in evening primrose oil, gamma-linolenic acid, is found in few other plants. Gamma-linolenic acid is normally manufactured when the body transforms linoleic acid into prostaglandins, hormonelike chemical messengers synthesized in most tissue cells. Prostaglandins regulate body functions such as smooth muscle contraction, blood pressure control, and responses to inflammation.
In some people, however, the conversion of cis-linoleic acid into prostaglandins is hampered because of aging, alcoholism, cancer, poor nutrition, radiation damage, or other factors. For these people, taking evening primrose oil can supply the gamma-linolenic acid needed to produce prostaglandins.
More than 120 studies in university hospitals in fifteen countries have been conducted on evening primrose seed oil. As a whole, the research suggests that the oil may be useful in treating conditions associated with imbalances or deficiencies of essential fatty acids. Some women with PMS have lower-than-normal levels of gamma-linolenic acid, suggesting that a glitch in the normal conversion of linoleic acid to gamma-linolenic acid may cause mood swings, fluid retention, breast tenderness, tension headaches, and other PMS symptoms.
Studies of the use of evening primrose oil to treat PMS have produced conflicting results. Participants in a double-blind crossover trial in Australia took evening primrose oil or a placebo over three menstrual cycles; for an additional three cycles, those who took the placebo originally received the treatment and vice versa. The researchers concluded that the benefits of evening primrose oil were statistically insignificant compared with the placebo.
However, other double-blind, placebo-controlled studies have shown that evening primrose oil significantly reduces irritability, breast pain and tenderness, and mood changes associated with PMS. Several clinical trials have found that its relief of breast pain and tenderness is comparable to that of conventional drugs with only mild adverse effects.
Although taking two 500-mg capsules of evening primrose oil three times a day with meals has been shown to correct essential fatty-acid imbalances associated with PMS, you may need to take them for as many as six menstrual cycles before relief of symptoms starts. For dosage information, see the box below.
Traditional Uses For Evening Primrose
Several North American Indian groups have used evening primrose for healing. The Iroquois boiled a sturdy taproot of evening primrose with a root of either field mint (Mentha canadensis) or self-heal (Prunella vulgaris) in a quart of water until the liquid was reduced by half. Hemorrhoid sufferers drank a cup of this decoction twice daily and also used it as an external wash. The Cherokee poulticed the root on hemorrhoids and drank a root tea to reduce weight. The Ojibwa soaked the entire plant in water, which they then applied to bruises.
Europeans began using the plant as a medicine during the eighteenth century. Johann David Schöpf, a German-born physician and author of a 1787 book on American medicinal plants, mentioned poulticing the fresh herb on wounds. The Shakers, who established the first commercial herb business in the United States, listed evening primrose in many of their catalogs, recommending applications of the leaves or roots to heal wounds and a tea of the leaf and root to settle an upset stomach.
In his classic Medical Botany (1847), Dr. R. Eglesfeld Griffith described a different application of the plant that hints of one modern use.
Some years since, hearing of the efficacy of a decoction of the plant in infantile eruptions, I made a trial with it in several cases of an obstinate character, which had resisted other modes of treatment, and became satisfied that it was highly beneficial; and this opinion has been confirmed by subsequent experience with it. The plant is to be gathered about the flowering season, and the small twigs with the bark of the large branches and stem, retaining the leaves with them, to be dried in the shade. Of these a strong decoction is to be made, with which the eruption is to be bathed several times a day.
Gamma-linolenic acid is a component of human breast milk. Sometimes, infants who are switched from breast milk to artificial milk formulas or cow’s milk lack a by-product of gamma-linolenic acid. This deficiency can lead to atopic eczema (dermatitis), which could be the “infantile eruption” Griffith referred to and treated with evening primrose. Recent clinical studies showed that evening primrose seed oil, when taken as a dietary supplement, produced a significant 20 to 25 percent improvement over controls in treating atopic eczema.
Taking Evening Primrose
Dose: Three to six 500-mg capsules a day is the common recommendation, or as many as twelve capsules. They should be taken with meals.
Cautions: In clinical studies, only a few cases of abdominal discomfort, nausea, and headache were reported by patients taking the herb for long periods. No known contraindications or drug interactions have been reported.
Note: Don’t be tempted to substitute borage seeds, another rich source of gamma-linolenic acid. Although they’re cheaper, they may contain toxic alkaloids.
Evening primrose oil capsules cost about 25 cents each and thus are relatively expensive when taken at the recommended doses.
Evening primrose oil products are registered in England for the treatment of atopic eczema. In Canada, evening primrose oil is an approved dietary supplement for treating deficiencies of essential fatty acids. In the United States, under the provisions of the Dietary Supplement Health and Education Act of 1994, it is considered a dietary supplement.
• Briggs, C. J. “Evening Primrose”. Canadian Pharmacy Journal 1986, 250:248–254.
• Brown, D. Herbal Prescriptions for Better Health. Rocklin, California: Prima, 1996.
• Horrobin, D. F. “Gamma Linolenic Acid”. Reviews in Contemporary Pharmacotherapy 1990, 1(1):1–45.
• Khoo, S. K., C. Munro, and D. Battistutta. “Evening Primrose Oil and Treatment of Premenstrual Syndrome”. Medical Journal of Australia 1990, 152:189.
• Olin, B. R., ed. “Evening Primrose”. Lawrence Review of Natural Products November 1993.
Steven Foster, author of Herbs for Your Health (Interweave, 1996) and many other books about herbs, is a member of the Herbs for Health Editorial Advisory Board. He lives and writes in Fayetteville, Arkansas.