I find that if my brain is foggy, drinking half of a sugar-free Red Bull can clear it up.
HOWEVER, I limit that to once every 3 weeks, at maximum. These drinks have an effect, so moderation seems… ah… whatever word implies "halfway between 'prudent' and 'necessary'".
They talked about this on the radio this morning. They said this particular drink had 7X the amount of caffeine in a normal RedBull