Evening primrose

Oenothera biennis

Native to North America, where it is regarded as a noxious weed, the evening primrose (Oenothera biennis L.) is considered by some authorities to be a complex of several closely related species. This biennial herb, a member of the family Onagraceae, produces a large number of highly fertile seeds, which are responsible for its introduction and establishment in Europe from ships' ballast in the first years of the seventeenth century. Although the native Indians and early European settlers in America used the whole plant for a variety of conditions, ranging from asthmatic coughs to gastrointestinal disorders to bruises, it is the fatty oil obtained from the small, reddish brown seeds that has caused a resurgence of interest in evening primrose.

Evening primrose seeds yield about 14 percent fixed oil that, in turn, contains approximately 9 percent of an unusual constituent, cis-gamma-linoleic acid (GLA). GLA is a known precursor of prostaglandin E1, serving as a key intermediate in the biosynthetic pathway leading from cis-linoleic acid to that prostaglandin. In fact, conversion of the predominant, essential dietary fatty acid, linoleic acid, to GLA is apparently a limiting step in prostaglandin production. Advocates of the use of evening primrose oil claim that increased intake of it produces a large number of beneficial effects, including, but not limited to, weight loss without dieting, lowered blood cholesterol, lowered blood pressure, cure of rheumatoid arthritis, relief of premenstrual pain, slowed progression of multiple sclerosis, and even the alleviation of hangovers.

Such claims require extensive clinical testing before they can be verified. Scientifically, they would be valid only if all of the specified conditions are favorably influenced by additional production in the body of prostaglandin E1 and if a deficiency of GLA is the single factor responsible for limited prostaglandin production. Both of these factors remain unproven. If they are not true, then assumptions of the efficacy of evening primrose oil in such conditions is somewhat like assuming one's car will run better if the gas tank is completely full instead of only half full.

Some clinical evidence exists supporting the possible efficacy of evening primrose oil in the treatment of premenstrual syndrome (PMS), mastalgia (sore breasts), multiple sclerosis, atopic eczema, various diabetes-associated problems, cardiovascular disease, rheumatoid arthritis, Sjogren's syndrome, endometriosis, and several other conditions. These studies, which have been reviewed and summarized in some detail, indicate that, at least in Britain, the oil is gaining some medical recognition.

However, the validity of some of the reports has also been refuted or at least questioned. An Australian study on the effectiveness of evening primrose oil in treating women with moderate PMS concluded that improvement was solely a placebo effect. Likewise, the methodology of the investigation reporting the utility of the oil in treating atopic eczema has been questioned. At least two clinical trials have shown benefits, particularly in relieving itch for moderate to severe eczema, reducing the need for topical and oral steroids, histamines, and antibiotics. However, two large trials showed no significant benefits. Furthermore, there are no data to support the safety of the long-term consumption of evening primrose oil. However, cis-linoleic acid is commonly consumed in the diet, and the amounts of GLA delivered by evening primrose oil corresponds to that produced from normal consumption of cis-linoleic acid. Wide availability as a dietary supplement for over fifteen years has resulted in few or no reports of toxicity. The proportions of GLA and cis-linoleic acid delivered in human milk is greater than that supplied by evening primrose oil at normal dosage range. When this evidence is taken together, safety seems well established. A potential drug interaction has been identified. Schizophrenic patients receiving phenothiazine epileptogenic drugs should avoid use of evening primrose oil as it could increase risk of temporal lobe epilepsy.

Other names

• Evening Star
• King's-cure-all
• Night Willow Herb
• Primrose
• Scabish

Parts used

Leaves, stem bark, flowers, seed oil, root.

Uses

The flowers, leaves, and stem bark of evening primrose have astringent and sedative properties. All three parts have been employed in the treatment of whooping cough. Evening primrose has also been taken for digestive problems and asthma, and used as a poultice to ease the discomfort of rheumatic disorders. The oil, applied externally, is beneficial in the treatment of eczema, certain other itchy skin conditions, and breast tenderness. Taken internally, the oil has an effect in lowering blood pressure and in preventing the clumping of platelets. The oil is now commonly taken for premenstrual problems, including tension and abdominal bloating. Multiple sclerosis may benefit from internal treatment with the oil, as may rheumatoid arthritis, intermittent claudication (a cramp like pain in the leg), and other problems relating to the circulation.
Evening primrose is also used to treat facial paralysis, hair problems, rosacea, and seasonal affective disorder (SAD).

Habitat & cultivation

Native to North America, evening primrose is now commonly found in many temperate zones around the world. Evening primrose thrives in open areas, especially in dunes and sandy soil. Evening primrose is grown commercially for its seed oil.

Constituents

Evening primrose oil is rich in essential fatty acids - cislinoleic (about 70%) and cis-gammalinolenic acid (about 9%) in particular. Its action mostly depends on the gammalinolenic acid (GLA), a precursor of prostaglandin E1. The oil is often combined with vitamin E to prevent oxidation.

How much to take

Evening primrose oil is available in 500-mg capsules. Most of the clinical trials have utilized doses of one or two capsules two or three times a day, with the maximum adult dose of 4 g daily. Up to three months may be needed to see a response in some conditions.

Side effects

Evening primrose oil, and by extension GLA, should not be consumed by schizophrenic patients taking phenothiazine drugs such as Compazine (prochlorperazine), Mellaril (thioridazine), Sparine (promazine), Stelazine (trifluoperazine), Thorazine (chlorpromazine), or Trilafon (perphenazine). The combination may increase the risk of epileptic seizure. Other drugs, such as Wellbutrin and other antidepressants, may also lower the seizure threshold and thus might interact with evening primrose oil.

Applications

FLOWERS:

INFUSION - Sip for headaches, feverish chills, or head colds and mucus.

TINCTURE - Take 5 - 10 drops for insomnia, anxiety, or overexcitement.

COMPRESS - Soak a pad in the hot infusion and apply to facial or trigeminal neuralgia.

OINTMENT - Use for sunburn and skin blemishes.

ESSENTIAL OIL - For insomnia, use 5 - 10 drops in bath water at night.

MASSAGE OIL - Dilute 5 - 10 drops oil in 25 ml almond or sunflower oil. Use for nerve pains, or apply to the temples for migraine.

ROOT:

DECOCTION - Take to clear the phlegm of stubborn coughs, especially chronic bronchitis. Can also relieve arthritis and rheumatism.

TINCTURE - Take a standard dose for the same ailments as the decoction.

COMPRESS - Soak a pad in the decoction for painful arthritic joints.

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