For most of us, it's a lifesaver. Coding till 3am, working for days straight without dropping a semicolon, being able to talk intellegently for weeks on end without sleep. Good thing, right?
For some of us.
It can kill
Yup, caffiene can kill you, especially if you have severed ADD/ADHD. Instead of acting as a stimulant, it acts as a depressent. I personally have had by heart rate lowered to barely 37 BPM and was unconcious for 3 days in the emergency room because I took 2 caffiene pills. While this is extreme, and I know that I have extremely severe ADHD, so I should have known better, but, if you have ADD/ADHD and it's pretty severe, be careful just how much caffiene you take into your system.
And I'm posting this cause I just got out of said hospital yesterday.