Inclusion Criteria:

1. The participant has a body mass index (BMI) within the range 18 to 40 kilograms per meter square (kg/m^2).
2. The participant has an International Classification of Sleep Disorders, Third Edition (ICSD-3) or International Classification of Sleep Disorders, Third Edition, Text Revision (ICSD-3-TR) diagnosis of NT1.
3. The participant has ≥4 partial or complete episodes of cataplexy/week (WCR).
4. The participant is positive for the human leukocyte antigen (HLA) genotype HLA-DQB1*06:02 or results from radioimmunoassay indicate the participant's cerebrospinal fluid (CSF) orexin (OX)/hypocretin-1 concentration is ≤110 picograms per milliliter (pg/mL) [or less than one-third of the mean values obtained in normal participants within the same standardized assay].

Exclusion Criteria:

1. The participant has a current medical disorder, other than narcolepsy with cataplexy, associated with EDS.
2. The participant: (a) has a history of myocardial infarction; (b) has a history of clinically significant hepatic disease, thyroid disease, coronary artery disease, cardiac rhythm abnormality or heart failure; or (c) has any medical condition (such as unstable cardiovascular, pulmonary, renal or gastrointestinal disease).
3. The participant has current or recent (within 6 months) gastrointestinal disease that is expected to influence the absorption of drugs.
4. The participant has a history of cancer in the past 5 years.
5. The participant has a clinically significant history of head injury or head trauma.
6. The participant has a history of epilepsy, seizure, or convulsion.
7. The participant has a history of cerebral ischemia, transient ischemic attack (<5 years from screening), intracranial aneurysm, or arteriovenous malformation.

Note: Other protocol defined Inclusion/Exclusion Criteria may apply.

Eligibility last updated 7/9/2024. Questions regarding updates should be directed to the study team contact.