In the latest study, 26 boys and 26 girls, age 12 to 17, took part in a series of experiments designed to measure the effect of various levels of caffeine.

Just what that something is isn't clear, but it's probably not caffeine, she said, because the effect has also been observed with decaffeinated coffee.

Of all the effects it has on our minds-enhanced attention and vigilance-perhaps least known is its tendency to make us more susceptible to persuasion.