Grapefruit Juice (GFJ)- I had toyed with the idea of using grapefruit juice for a long time but have read mixed reports. Recently I read that it doesn't inhibit CYP2D6 but rahter 3A4 which is responsible for conversion of codeine into norcodeine. In theory by inhibiting 3A4 you leave more codeine for 2D6 to turn into morphine. After reading this I decided to bite the bullet and give it a go. I had about 200ml of store bought grapefruit juice and about 100ml of squeezed juice around an hour before drinking my codeine. It definately seemed to increase the effects of both the codeine and the diazepam I took. I would say it potentiates diazepam/valium more than codeine but it does potentiate both. It is not a miracle potentiator and it definately does not potentiate codeine to a large extent, I found it to taste pretty gross personally and it isn't terribly cheap. Some people might not find it worth the mild potentiation it causes, if one is combining valium with their codeine I would say it is more worthwhile. I will be using it again, although the bitter taste is a bit of a deterrant for me, personally I would rather drink CWE! At this stage I have only used the red grapefruit juice and it seemed to work well enough, I have been advised that white grapefruit juice is better for potentiation purposes of both codeine and benzodiazepines.