Caffeine, the circadian clock, and sleep
Ouch!! "Many people worldwide consume caffeine daily. Normal dietary consumption is sufficient to antagonize up to 50% of the inhibitory A1 and the facilitatory A2A adenosine receptors in the brain (2, 3). This increases alertness and allays drowsiness and fatigue, but may also induce restlessness and prolong the time to fall asleep, enhance nighttime wakefulness, and reduce the depth of sleep (4)." Full news article @ Science.