Grapefruit Juice (GFJ)- I had toyed with the thought of applying grapefruit juice for a long period but have examine blended reports. Not too long ago I read through that it isn't going to inhibit CYP2D6 but rahter 3A4 and that is responsible for conversion of codeine into norcodeine. In concept by inhibiting 3A4 you allow additional codeine for 2D