Diagnosis and Criteria for Inclusion:

Patients are included in the study if all of the following criteria are met:

• Written informed consent is obtained
• The patient is an outpatient, man or woman of any ethnic origin, 18 to 65 years of age (inclusive)
• The patient has a complaint of excessive sleepiness
• The patient has a current diagnosis of narcolepsy according to ICSD criteria.
• The patient is in good health as determined by a medical and psychiatric history, physical examination, electrocardiogram (ECG), and serum chemistry and hematology.
• Women must be surgically sterile, 2 years postmenopausal, or, if of child-bearing potential, using a medically accepted method of birth control (ie, barrier method with spermicide, steroidal contraceptive [oral, implanted, and Depo-Provera contraceptives must be used in conjunction with a barrier method], or intrauterine device [IUD]) and agree to continued use of this method for the duration of the study.
• The patient has a mean sleep latency of 6 minutes or less as determined by the Multiple Sleep Latency Test (MSLT) (performed at 0900, 1100, 1300, and 1500).
• The patient has a CGI-S (Clinical Global Impression of Severity of Illness) rating of 4 or more.
• The patient does not have any medical or psychiatric disorders that could account for the excessive daytime sleepiness.
• The patient is able to complete self rating scales and computer-based testing.
• The patient is willing and able to comply with study restrictions and to attend regularly scheduled clinic visits as specified in this protocol.

Criteria for Exclusion:

Patients are excluded from participating in this study if 1 or more of the following criteria are met:

• has any clinically significant, uncontrolled medical or psychiatric conditions (treated or untreated)
• has a probable diagnosis of a current sleep disorder other than narcolepsy
• consume caffeine including coffee, tea and/or other caffeine containing beverages or food averaging more than 600 mg of caffeine per day
• used any prescription drugs disallowed by the protocol or clinically significant use of over the-counter (OTC) drugs within 7 days before the second screening visit
• has a history of alcohol, narcotic, or any other drug abuse as defined by the Diagnostic and Statistical Manual of Mental Disorders of the American Psychiatric Association, 4th Edition (DSM IV)
• has a positive UDS at the screening visit
• has a clinically significant deviation from normal in the physical examination
• is a pregnant or lactating woman. (Any woman becoming pregnant during the study will be withdrawn from the study.)
• has used an investigational drug within 1 month before the screening visit
• has any disorder that may interfere with drug absorption, distribution, metabolism, or excretion (including gastrointestinal surgery)
• has a known clinically significant drug sensitivity to stimulants or modafinil