[10] It reduces the amount of codeine converted by CYP3A4 into norcodeine thus increasing the amount metabolized into
morphine.
Morphine itself, however, is not affected by
grapefruit juice, as it is not metabolized by the cytochrome P450 system.
* Cyclosporine (Neoral). Blood levels of cyclosporine are increased if taken with grapefruit juice. A plausible mechanism involves the combined inhibition of enteric CYP3A4 and P-glycoprotein, which potentially leads to serious adverse events (e.g.