context: Evening primrose is a plant that's native to Europe and North America. It has a long history of medicinal uses. Native Americans, for example, used its leaves, roots, and seedpods in preparations for hemorrhoids, bruises, wounds, and skin problems. Evening primrose oil contains an omega-6 essential fatty acid that is necessary for good health. However, while there is some evidence that taking evening primrose oil supplements may benefit some health conditions, the study results are mixed.. Most of the studies have been small and further research is needed. Evening primrose oil supplements usually come in capsule form. People take it to try to treat conditions such as: Rheumatoid arthritis Premenstrual syndrome ( PMS) Eczema or atopic dermatitis and other skin conditions Breast pain during menstruation ADD Asthma Reviews of the available scientific evidence have found no reason to recommend evening primrose oil to help the symptoms of premenstrual syndrome or breast pain. There is some good research showing that evening primrose oil may be helpful in eczema or atopic dermatitis. And some studies suggest that supplements that contain gamma-linolenic acid ( GLA), including evening primrose oil, may be of some benefit to people with rheumatoid arthritis. But other research is conflicting, so more research is needed on the use of evening primrose oil for both of these conditions. Evening primrose oil has also been used as a complementary treatment for some cancers. Again, evidence to support such use is lacking. GLA, thought to be the active ingredient in evening primrose oil, can be found in small amounts in a variety of food sources. However, it is most concentrated in plant oils such as evening primrose oil and borage oil. The doses used in most clinical trials would be hard to get from food sources. Most people will tolerate evening primrose oil without complications. But keep in mind that there have been reports of side effects such as: Headache Stomach upset Nausea Dizziness Rash Evening primrose oil may raise the risk of bleeding among people who take anticoagulant and antiplatelet medications. It may also raise the risk of seizures as well as serious nausea and vomiting for people taking a class of drugs known as phenothiazines. These drugs are used to treat schizophrenia and other psychotic disorders. People should be especially cautious about taking evening primrose oil if they have: Bleeding disorders Seizure disorders such as epilepsy Mania Also, people who take medication to lower blood pressure should be careful, because evening primrose oil may cause a further drop in pressure. Evening primrose oil may also interact with certain medicines used to treat depression. Several other drug interactions have been noted. Evening primrose oil may cause seizures if used with anesthesia. Make sure you tell your doctor if you are taking this before you have any surgery. Pregnant women should not take evening primrose oil because of the potential for complications. Before taking evening primrose oil, or any other supplement, talk to your doctor about potential risks and drug interactions. Even so-called natural supplements should be used with caution. The U. S. Food and Drug Administration ( FDA) does regulate dietary supplements; however, it treats them like foods rather than medications. Unlike drug manufacturers, the makers of supplements don't have to show their products are safe or effective before selling them on the market.