I'm in the same boat, although I preferred Monster drinks. They were the most effective (legal) productivity booster that I've yet to find, but eventually I needed 5 just to get through the day and started to notice a lot of side effects to be health, in terms of sleep quality and my stomach.

Sadly, I don't do moderation well, so it's on my list of things I used to love but can no longer tolerate. Right up there with cola, sugar, tobacco, and alcohol.