I've been pretty impressed by the results of L Glutamine. When I am feeling out of sorts.. Dark eye circles, concentration problems, anxious, I have found a good tablespoon of this (powder) in a glass of water can really help normalize my state. I am not exactly sure how it is working in my system but I suspect it has to do with my intestinal health and immunity. The Leaky Gut theory seems to be gaining credibility and this may be a remedy for it.. I am a firm believer in taking a break from supplement or only taking them when you feel a need and this is one I like to have around.