Coffee abuse  

Scientists have confirmed what caffeine users already know: that to maintain caffeine levels in the blood, it's important to keep consuming it in small doses (or large doses, as the case may be) throughout the day. But at the same time, I'm not sure it's surprising that people go for a big dose in the morning. Rsearch on users of more ilicit drugs suggests they like two things: a relatively small, constant dose, as well as occasional spikes. There's no reason to expect caffeine users to be any different.