Grapefruit Juice (GFJ)- I'd toyed with the idea of employing grapefruit juice for some time but have read through blended studies. Not long ago I read that it does not inhibit CYP2D6 but rahter 3A4 and that is chargeable for conversion of codeine into norcodeine. In idea by inhibiting 3A4 you allow a lot more codeine for 2D6 to turn into morphine.