I'm not a doctor or anything, but it has 10 calories listed on the label, so there's something in there that has the potential to break your fast.
Not that it's a bad thing, but if your goal is to stay fasted through the morning, then it might be counter productive.
I'm a real sugar kind of guy. I can't stand stevia or artificial sweeteners, they all taste like a chemical factory to me. I get my caffeine from black coffee though, a guy doesn't need much more than that in the morning.