I've read several times that caffeine stops absortion of glutamine (most recently in the GNC pr mag). In the very next statement they said that the stackers weren't affected without saying why not. The search didn't turn up anything definitive but maybe I'm not searching for the right topic. This is fairly trivial but I don't take many supplements and would prefer not to waste the ones I am taking.
It's possible that the combination of caffeine and ephedrine allows for glutamine absorption. Anyway, when I take stackers, I make sure I allow a few hours before taking Glutamine.