I know someone who has drunk a mixture of ground 4g Syrian Rue seeds, caffeine and grapefruit juice Syrian Rue seeds contain quinazolines. While I'm not entirely sure what quinazolines do (sorry but I've never taken them or really heard much about them myself, I think they are some sort of mild stimulant with visuals?) I know that my friend lived and had a 2-3 hour trip which he enjoyed a lot. The only thing you may need to be worried about are the MAOI effects of quinazolines, personally I'm scared out of my mind of MAOIs since a bad experience a while ago but I don't think that there is any major reaction that is likely to happen with grapefruit juice, or at least not based on the one person I know who has consumed both.