Right now, it is only approved for use in narcoleptics suffering from excessive sleepiness during the day.

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When it goes on sale under the brand name Xyrem later this year, it could help thousands of narcoleptics.

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Worries about the potential for abuse have led the FDA to approve the drug only for narcoleptics who suffer from cataplexy.

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For narcoleptics, however, this sedative may provide some much-needed relief.

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There are also more insidious effects: Many narcoleptics experience vivid hallucinations while falling asleep, and between 60% and 90% suffer from a dangerous condition called cataplexy, in which muscles become spontaneously paralyzed.

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But its maker, Cephalon (nasdaq: CEPH - news - people ), says that 80% of prescriptions are probably written out to people who are tired for other reasons, not narcoleptics.

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