Bit of a waste of time. Caffeine is a stimulant, a real drug just like any other. A drug being legal does not make it less a drug. Caffeine tolerance is real and involves changes to brain chemistry : http://www3.interscience.wiley.com/journal/113369008/abstrac... Coffee delivers high doses of caffeine, which works by stimulating adrenaline http://health.howstuffworks.com/caffeine-awake.htm production... so if you stay hooked on a stimulant for a long time, of course it has a negative effect on your performance.