Narcolepsy Clinical Trials

⁃ Participants must meet all of the following criteria to be included in this study:

• Male or female, age greater than or equal to (\>=) 18 years (or as regionally appropriate) at the time of informed consent

• NT1 Cohort: Must fulfill Inclusion Criteria 2a and 2b

‣ Diagnosis of NT1 within the last 10 years of screening, as confirmed by at least one of the following:

• Polysomnography (PSG) and Multiple Sleep Latency Test (MSLT) results, and clinical history, consistent with the 2023 International Classification of Sleep Disorders, 3rd edition, text revision (ICSD-3-TR) criteria for NT1

∙ Cerebrospinal fluid orexin-A/hypocretin-1 concentration less than or equal to (\<=) 110 picograms per milliliter (pg/mL)

⁃ At least 4 or more episodes of cataplexy/week as averaged over 2 weeks minimum and confirmed by the cataplexy portion of the Diary If PSG or MSLT results are not available within the last 10 years of screening to fulfill Criterion 2a then screening assessment results for PSG or MSLT can be used instead

• NT2 Cohort: Diagnosis of NT2 within the last 10 years of screening, as confirmed by PSG and MSLT results, and clinical history, consistent with the 2023 ICSD-3-TR criteria for NT2 If PSG or MSLT results are not available within the last 10 years of screening to fulfill Criterion 3 then screening assessment results for PSG or MSLT can be used instead

• ESS score \>=10

• Reports regular bedtime, defined as the time that the participant attempts to sleep, between 22:00 and 01:00 (based on data from the screening Diary)

• Reports regular waketime, defined at the time the participant gets out of bed for the day, between 05:00 and 10:00 (based on data from the screening Diary)

• Reports being in bed between 7 and 9 hours per night (based on data from the sleep portion of the Diary)

• Compliance rate \>=80 percentage (%) for completion of the Diary during screening

• Body mass index (BMI) \>=18 to less than (\<) 35 kilograms per square meter (kg/m\^2) at Screening