A flavonoid (plant pigment) compound found in grapefruit, naringin gives grapefruit its characteristic bitter flavor. Grapefruit processors attempt to select fruits with low naringin content, and often blend juices obtained from different grapefruit varieties to obtain the desired degree of bitterness. Naringin is believed to enhance our perception of taste by stimulating the taste buds; that's why some people consume a small amount of grapefruit juice before a meal.
But there are downsides to the healthy fruit.
Previous research has found that naringin interferes with enzymatic activity in the intestines thus slowing the breakdown of certain drugs and resulting in higher blood levels of the drug. A number of drugs that are known to be affected by the naringin in grapefruit include calcium channel blockers, estrogen, sedatives, medications for high blood pressure, allergies, AIDS, and cholesterol-lowering drugs. Consuming grapefruit or grapefruit juice may also extend caffeine levels and effects of caffeine.
While the effect of naringin on the metabolism of a drug can increase the drug's effectiveness, it can also result in dosages that are inadvertently too high. Therefore, many physicians do not recommend that patients take any drugs with grapefruit juice unless the interaction with the drug is known. In addition, the effects of drinking grapefruit juice is cumulative, which means that if you drank a glass of grapefruit juice daily with your medication for a week, the drug interaction would be stronger at the end of the week than at the beginning.