Consumption of energy drinks containing caffeine may have beneficial effects on exercise but probably not on mental function.
The effects of pre-exercise caffeine consumption by trained cyclists on racing times and cognitive performance were measured and are reported in Research Journal of Caffeine.
Race performance improved for all study participants after consuming an energy drink, even if they already had an elevated blood caffeine level before the energy drink.
Cycling times improved by an average of 3% for the group and the research also reported improvements in certain aspects of cognitive function, but these were probably not due to the energy drink.
The article “Effect of an Energy Drink on Physical and Cognitive Performance in Trained Cyclists.” is available for download at the Research Journal of Caffeine website.
One would have to read the study to offer a valid opinion, but one aspect strikes me immediately: did they differentiate between those with “abnormal” executive function (ie: ADD) and those without? As an ADD-er, I can attest that my IQ goes up about 30 points with my first cup of coffee in the morning!