It is thought that they quickly become dependent on caffeine and so wake up suffering mild withdrawal symptoms, after being denied their "fix" overnight. Britain's Bristol University took part.
From the March 13, 2007, Prepared Foods e-Flash
Caffeine Myth
March 7/Hobart Mercury (Australia) -- New research suggests the benefits of caffeine could have been exaggerated, with regular coffee and tea drinkers being no more alert after their first cup of the day than those who never touch the stuff.