Grapefruit Juice (GFJ)- I had toyed with the thought of making use of grapefruit juice for a very long time but have read through blended experiences. A short while ago I examine that it will not inhibit CYP2D6 but rahter 3A4 and that is responsible for conversion of codeine into norcodeine. In theory by inhibiting 3A4 you permit much more codeine