The drug being tested in this study is called TAK-861. TAK-861 is being tested to treat people who have narcolepsy without cataplexy [Narcolepsy Type 2 (NT2)]. This study will evaluate the efficacy, safety, and tolerability of 2 oral doses of TAK-861.~The study will enroll approximately 60 patients. Participants will be randomly assigned (by chance, like flipping a coin) to one of the three treatment groups-which will remain undisclosed to the patient and study doctor during the study (unless there is an urgent medical need):~TAK-861 Dose 1~TAK-861 Dose 2~Placebo (dummy inactive pill) - this is a tablet that looks like the study drug but has no active ingredient~This is a multi-center trial to be conducted worldwide. The overall time to participate in this study is approximately 18 weeks.
The main aim is to evaluate the effect of TAK-861 on symptoms of narcolepsy, including excessive daytime sleepiness (EDS) as measured by sleep latency from the Maintenance of Wakefulness Test (MWT).~The study will enroll approximately 60 participants and they will be randomly assigned to 3 groups (20 per group) to take one of two different doses of TAK-861 or a placebo. All the participants will receive the treatment for 8 weeks. Participants will be asked to complete some questionnaires during the study. This trial will be conducted in North America, Europe, and Asia Pacific.