Sometimes it does, but people vary wildly in how they react to caffeine. I don't notice a difference in sleep - I tend to wake up well-rested about 75-85% of t

Sometimes it does, but people vary wildly in how they react to caffeine. I don't notice a difference in sleep - I tend to wake up well-rested about 75-85% of the time (A monthly cycle of hormones definitely affects sleep and wakefulness). I've experimented, and drink more than 3 cups. I also don't get the pick-me up some folks get. My father drank more than 3 cups per day - my parents would split a pot of coffee between them - but he drank decaf after noon. If he didn't stop caffeine, he couldn't fall asleep at night.