I have before, but moreso as a mood/cognitive-enhancer, but did notice a positive effect in energy levels. However, it brought on some rather nasty side-effects for me: heart palpitations (and it was impossible to fulfill a cardio workout while taking), and despite the cognitive enhancement I had experience with it (which I was definitely impressed by) I tended to overfocus a lot more, and became angry easier. Talking to people was much easier for me, however they all thought I had a bug up my ***, unfortunately, because otherwise it would be all I ever needed. I still take it from time to time though, but only what's in each serving of Whey I drink. Good luck btw, and if I were you, I would separate the doses throughout the day at first, so you get a feel for it and not experience something like I did (especially the heart palps.).