Caffeine Metabolism: A great article going over the pathway  Caffeine  takes to get into your system and how it effects you once it does. I was  originally  pulled in by the spiffy image but the  rest of the article is very worth your time if you are in any way interested in how caffeine changes you.

Caffeine  begins  to effect you in as little as ten minutes and by the time the next hour rolls around your body has already metabolized over 99% of the chemical. Think of it this way Caffeine is a plant toxin,    it just happens to have a very  pleasant  side effect of waking you up while your body attempts to get rid of it.