Evening primrose oil is obtained from the seeds of the plant by pressing. The oil can be taken directly as a liquid or in the form of capsules. Evening primrose oil is considered a useful dietary supplement because it is a good source of essential fatty acids (EFAs), Omega 6 predominantly. EFAs are called essential fatty acids because the human body cannot produce them; they must be obtained from the diet. EFAs maintain the function of cell membranes, regulate pain and inflammation, prevent blood clots, regulate blood pressure and cholesterol levels, and help to produce hormone-like substances known as prostaglandins. Prostaglandins function as inflammation mediators in the short-term regulation of glands and other body organs. It is thought that evening primrose oil relieves the symptoms of PMS by preferentially stimulating anti-inflammatory prostaglandins.