Coffee has a two edged sword. It's one powerful fat mobiliser at the cellular level and a CNS stimulant, which is great for making you alert. That's great.
Consume too much in one sitting and and it'll be like taking a mini speed tablet (not that I've taken one before) but have seen the effects first hand: and it's not a pretty sight.
What's too much? Everyone has a differnt threshhold. I don't drink coffee at all and it acts like a drug on me if I was to consume it. Stopped it at the age of 15 with soft drinks.
Fadi.