Mathematician Paul Erdős famously took amphetamines regularly.

http://en.wikipedia.org/wiki/Paul_Erd%C5%91s "Ron Graham bet him $500 that he could not stop taking the drug for a month. Erdős won the bet, but complained that during his abstinence mathematics had been set back by a month: 'Before, when I looked at a piece of blank paper my mind was filled with ideas. Now all I see is a blank piece of paper.' After he won the bet, he promptly resumed his amphetamine use."