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psisci said:
Yes it can as it has an ingredient that competes for the liver enzyme needed to metabolize certain meds. However, unless you have severe liver disease, it would take about 15 grapefruits right before your med to have any real effect.

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I'm a little concerned about blanket statements such as this one. There are far too many variables than to generalize in this way. For some drugs, the grapefruit effect is quite dramatic. The statin drug Simvastatin demonstrated an AUC (total drug exposure) increase of 1250%, with Cmax (peak blood concentration) increased 1104%. Buspar (buspirone) showed ncreased Cmax of about 4-fold, and increased AUC 9-fold. Luvox (fluvoxamine) more than doubled, whereas Zoloft (sertraline) and Tegretol (carbamazepine) increased by about 50%. There is a real risk of over-sedation from most benzodiazepine drugs. Someone accustomed to taking a benzo before getting into their car could be seriously impaired by washing it down with grapefruit juice.

The studies which provided the numbers I reference above used doses of between 200 mL and 1200 mL grapefruit juice per day. Even at the maximum tested, that's less than 15 fruits. And the inhibition zone that matters most is not in the liver; it is in the intestinal wall. Bioavailability of the drugs is what is most affected (intestine), not half-life (liver).

Lar