Laurie Coots, a marketing executive who flies to meetings in other countries twice a week, spent years trying to conquer sleepless nights and chronic jet lag. But nothing worked, she says, and every day was a struggle to stay awake. "It was debilitating," said Ms. Coots, 46, who is from Los Angeles. "I couldn't give an effective presentation because I was always shaky and nervous from being amped up on caffeine and stimulants." Then she found modafinil, a small white pill that revs up the central nervous system without the jitteriness of caffeine or the addiction and euphoria of amphetamines....