The initial portion of the protocol involves discontinuing any medications for cataplexy that the patient may be taking. Subsequently, the patient is prescribed a dose of oral solution of study drug or placebo over a 10-11 week period. During the trial, narcolepsy symptoms will be evaluated. Participants are allowed to continue using stimulant medications at constant doses during the study. A total of 1 to 3 daytime visits in addition to 4 overnight visits to the sleep center will be required to complete the study.