The study suggests regular coffee drinkers seem to need caffeine to return to their normal state of alertness. And to avoid the side effects of caffeine withdrawal such as headaches. That runs counter to the belief that caffeine offers some added boost in alertness.
Scientists say, although caffeine consumers feel alerted by caffeine, the effect is actually only bringing you back from caffeine withdrawal-induced low-level alertness.
So, you're not gaining anything over and above a non-caffeine drinker.
The study appears in Neuropsychopharmacology.