An old Native American herb. The evening primrose grows like a weed. Not really a primrose, it is sometimes called "sun drop." The large yellow flower opens late in the day and last only one evening, then produces lots of small seeds. Presumably, these seeds were carried to Europe early in the history of colonization of North America because evening primrose now grows wild in many parts of the continent.

The oil of evening primrose has a high content of gammalinolenic acid (GLA), which is converted by your body into prostaglandins (fatty acids that act a lot like hormones) producing a wide range of effects on your body. It supplies many essential fatty acids the body needs to maintain optimal health. Essential fatty acids are as important to good health as vitamins and minerals. Studies show that evening primrose oil might help lower blood cholesterol, can reduce the discomfort associated with premenstrual syndrome, is used to treat eczema and is a traditional remedy for arthritis. Evening primrose oil may even correct the body's imbalances that cause mood swings, irritability and breast tenderness. The strongest evidence for efficacy is in the treatment of atopic dermatitis when the skin is itchy, red, scaly, dry, and inflamed.

Evening primrose to be used for herbal medicines is commercially cultivated and carefully bred to yield constant levels of the essential fatty acids in the seeds. Growers in the United States and Canada alone produce three hundred to four hundred tons of seeds each year. Oil from the seeds is the only part of the plant currently used. Approximately 70 percent of the oil is cis-linoleic acid, and as much as 9 percent cis-gamma-linolenic acid (GLA) which is a rare find in plants.

Most over-the-counter pain relievers and many prescription arthritis medicines work primarily by blocking prostaglandin synthesis, however prostaglandins play an important role in many biochemical reactions. 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.  Usual dosage is around 500-1,000 mg a day.