Originally Posted by JustJess

How does caffeine keep us awake, you ask? What a good question!
Not that I've gotten this far in my studies as yet, but this site is pretty useful. It seems that our little friend increases our dopamine levels, making us happy (in the same way that cocaine and heroin do! Yippee!), and interferes with our absorption of adenosine, which is the hormone that puts us in a deep healthy sleep. Without that hormone at sufficient levels, we never really go beyond a light, wakeful sleep. So we think we're resting (sometimes)... but we're not. How thrilling for all of us. And the worst part is how long it stays in our system - one site actually describes it as half-lives (how long it takes for one half of an amount of material to decompose, or in this case, pass out of the system): according to the HowStuffWorks (link above), it takes 6 hours for half of the caffeine to pass out of your system. So if you drink coffee at 5:30pm like moi, 11:30pm is not going to be a very good bedtime because half of that caffeine is still floating around in there.