Stacker 2 was a fat burner to the last of my knowledge. So unless you want to lose weight too, shy away from those.

I've taken a couple No-Doz's every now and then, like when I had 2 hours of sleep and had to get up early or before a long night of drinking. It's a hell of a lot more effective than any caffeine drink. The only horrible side-effect was that whenever I smoked, it gave me this terrible overwhelming and uneasy feeling. Not fun! They do work well, but you can become hooked easily and if you take to many, you won't be able to function at all, and instead only quivering and shaking.

Good luck :>)