‘Grapefruit juice has been shown to affect the metabolism of several drugs. Included in the list of potential target drugs are diazepam, cisapride, cyclosporine, felodipine and other dihydropyridine calcium channel blockers, midazolam, nisoldipine, triazolam, saquinavir, lovastatin, and atorvastatin. The mechanism of this interaction appears to primarily result from inhibition of enzymes in the intestinal wall.
Several constituents of grapefruit juice have been implicated including the flavonoids naringin and naringenin, along with the furanocoumarins, bergapten and 6,7-dihydroxybergamottin. Unfortunately, the content of these varies between different grapefruit juices and varieties of fruit, making it impossible to determine if one is safer than another.’