I think this has been covered by everyone's comments so far; but naturally, the different types of energy drinks and their chemical compositions will react to others in different ways.
For me, it does jack. I've plowed down 8 coffee's and a can of Mother (which claims to be max legal caffeine in a larger can) over a work day with no food, and came out fine. But I'd started drinking coffee (and even a little liqueur) when I was 10. Small amounts, of course. But I bare in mind, an energy drink is essentially the Soft Drink equvilant of a coffee, or to be exact; Mother = 160mg Caffeine (I recall, probably wrong), Espresso = approx 90mg - So there you have it, coffee marketing in high doses for adolescents. ^_^
but take this into account; as mentioned in previous posts, energy drinks contain B vitamins (and they 
must contain them too). B vitamins assist as regulators for energy release. Take them away and you've got a hell of a lot of energy pumping through you at an possibly dangerous rate.
Once in high school, some friends would drink energy drinks every day at lunch. They came in one day after consuming 2/12 cans of V each, and were coming down until the end of the day.
Makes me wonder a bit though. How many factors can cause this. Because they've never come down badly before. And me, being able to handle some much, never have a problem at all. But from a biological point of view; each body is to it's own. Some may just urinate out most of it because their kidneys work so hard to get it out. Others probably just have it floating around for too long, possibly causing affects like Kaz felt. In other cases, perhaps the amount consumed should e regulated based upon recent dietary intake, and even the amount of solid food matter in your gut. (More may be bad due to absorption; it's called theory for a reason).
Anyway, I'm ranting. so I'll stop there. 

 :lol