Straight out of Paul Hoffman's biography of Paul Erdös:
Erdös first did mathematics at the age of three, but for the last twenty-five years of his life, since the death of this mother, he put in nineteen-hour days, keeping himself fortified with 10 to 20 milligrams of Benzedrine or Ritalin, strong espresso, >and caffeine tablets. "A mathematician," Erdös was fond of saying, "is a machine for tuning coffee into theorems." When friends urged him to slow down, he always had the same response: "There'll be plenty of time to rest in the grave."
Paul Erdös is my favorite mathematician. One of his friends challenged him to stop taking Benzedrine. According to Erdös' friend, Erdös was an addict and would not be able to give up Benzedrine. However, Erdös proved him wrong by not taking Benzedrine for a month. The result? Erdös just stared at a blank sheet of paper for a whole month. Although Erdös won the wager, he remarked that his friend had set mathematics back a whole month because Erdös had no ideas.