Grapefruit Juice (GFJ)- I'd toyed with the thought of applying grapefruit juice for a very long time but have study mixed experiences. Just lately I study that it doesn't inhibit CYP2D6 but rahter 3A4 and that is to blame for conversion of codeine into norcodeine. In concept by inhibiting 3A4 you permit more codeine for 2D6 to change into morphine.