I'm actually using Elix1r at this very moment to help keep me sharp working the night shift! I absolutely love this stuff, a full serving in a shaker bottle full of ice and cold water, and its hard to beat. The flavor is just fantastic. Since I typically work odd hours, night shift or swing shift, I find I'm usually pounding energy drinks or chugging coffee, but after several years it just doesn't get the job done anymore. Since I started using Elix1r I'm not just awake, I'm on point. Focused, dialed in, and ready to go. Which is perfect, because my job has moments where my reaction time and decision making skills can mean life or death! I can't afford to be off my game, I have to be ready at a moments notice. I haven't built up a tolerance to it, nor have I had any side effects, and I've been using it for about a month and a half now! Not daily, mind you. But just about. I prefer it over grabbing a Monster or Red Bull, not that I don't like their taste from time to time, but they don't deliver energy like Elix1r delivers energy!