"The team demonstrated that stopping daily caffeine consumption produces changes in cerebral blood flow velocity and quantitative EEG that are likely related to the classic caffeine withdrawal symptoms of headache, drowsiness and decreased alertness."
What is even more surprising is that they found no net benefit of using caffeine:
"In contrast to what most of us coffee lovers would think, our study showed no difference between when the participant was maintained on chronic placebo and when the participant was stabilized on chronic caffeine administration. What this means is that consuming caffeine regularly does not appear to produce any net beneficial effects, based on the measures we examined."
I will just stick to tea and cola then. Oh, wait.