Research about the interaction of grapefruit
juice with drugs suggests that compounds in grapefruit
juice, called furanocoumarins (for example, bergamottin), may be responsible for the effects of grapefruit juice. Researchers believe that furanocoumarins block the enzymes in the intestines that normally break down many drugs. One glass of grapefruit juice could elicit the maximum blocking effect, and the effect may persist for longer than 24 hours.