It is well known that even 1/2 a grapefruit or one glass of juice can reduce an enzyme called cytochrome P450 (CYP 450) by 50% for up to 24 hours. This is important because some medications such as atorvastatin, amlodipine, carbamazepine and one of our newest medications for rheumatoid arthritis, tofacitinib (Xeljanz) need this enzyme to be eliminated from the body.
If grapefruit juice is combined with these medications, they could accumulate in the body increasing the potential for adverse effects. Therefore, it is recommended that grapefruit not be ingested with medications requiring this enzyme for processing. Not all fruits contain furanocoumarin derivatives which seem to be the culprit in affecting this enzyme.
However, lab studies indicate that pomegranate, pomelo, black mulberry juice, wild grape juice, and black raspberry juice also interfere with CYP3A4. Pomegranate is now known to have as significant an impact as grapefruit.