Oil from the seeds of the evening primrose plant contains gamma-linolenic acid (GLA), which is one of the two main kinds of essential fatty acids. GLA is an omega-6 fatty acid; the other type is omega-3. The body converts GLA into prostaglandins and leukotrienes, which can affect pain and inflammation. GLA may help the body produce anti-inflammatory prostaglandins. Evening primrose oil is one good source of GLA, but borage oil contains even more.
(Source: Natural Treatments for Fibromyalgia: An A to Z Guide, by Kenna Simmons. An official publication of the Arthritis Foundation. To purchase, visit www.arthritis.org.)