"I felt great all day and for a number of days after that," she says. The drug worked so well that she gave her husband some when he complained of feeling groggy.

Matt Parsons couldn't get through the day without drifting into an exhausted stupor. Barely 30, the Midlothian, Virginia, office manager always woke up feeling like he hadn't slept at all. He started calling in sick to work. When he did show up, he didn't accomplish much.

Eventually, he was diagnosed with a disorder that caused his limbs to jerk uncontrollably, disrupting his sleep. Anti-seizure medicine was ruled out because of the side effects. Instead, his doctor prescribed Provigil. An hour after taking his first pill, he remembered that his living room needed painting: "I looked over at the paint cans," he says, "got up, did all the prep, and painted the wall that evening."

A California lawyer had no medical reason to take the drug, but he did have a common complaint: "I work 10 to 14 hours a day, so I would have no personal life if I didn't sacrifice some sleep," he told an online support group. He now takes Provigil four times a day. "At the right dosage," he reported online, "this wonder drug is really great."

These aren't the only people enthusiastic about Provigil. Some sleep scientists have been impressed by its potential since the FDA approved modafinil (Provigil's generic name) in 1998. Sold by drugmaker Cephalon, the drug induces wakefulness without stimulating virtually the entire nervous system -- an impossibility for its pharmaceutical predecessors, Ritalin and amphetamines. "Provigil works in a much more localized part of the brain, the hypothalamus, which controls the sleep-wake cycle," says Cephalon senior vice president Paul Blake.