The Food and Drug Administration ruled that Simi Valley-based Pharmanex Inc. can no longer sell its Cholestin without obtaining regulatory approval. The privately held company promotes Cholestin as a dietary supplement that can help reduce cholesterol levels. The FDA said, however, that Cholestin requires regulatory approval because it contains lovastatin, the active ingredient in Mevacor, a cholesterol-lowering drug sold by Merck & Co. Pharmanex denies that Cholestin is a drug. President William McGlashan said the product is made primarily of rice and food yeast grown on rice. The yeast contains a natural chemical known as mevinolin, which when crystallized does turn into lovastatin. Mevinolin, however, has long been in the food supply naturally, McGlashan said. Pharmanex is fighting the decision and has a hearing scheduled in a federal court in Utah on June 15. It will continue selling Cholestin pending a court ruling.