Naringin

Naringin is a natural chemical compound known as a bioflavonoid found in grapefruit, giving it its bitter flavor. Hence, the food industry, however, uses naringin as a bitter in "tonic" beverages, bitter chocolate, ice cream, and ices.Naringin also works synergistically with other nutrients, increasing the bio-availability (how much nutrient is absorbed by the body) and therefore maximizing the health benefits of these nutrients.
Of course, it is important to note this citrus extract interferes with enzyme activity in the intestines, and therefore can inhibit the breakdown of certain drugs. That is why you should consult with your physician if you are on any medication before eating grapefruit.