The drug being tested in this study is called TAK-861. This study will look at the effect of TAK-861 on improvement in narcolepsy symptoms, including excessive daytime sleepiness (EDS) and number of cataplexy episodes.~The study will enroll approximately 100 patients. Participants will be randomly assigned (by chance, like flipping a coin) to one of the five treatment groups which will remain undisclosed to the participant and study doctor during the study (unless there is an urgent medical need):~TAK-861 Dose 1~TAK-861 Dose 2~TAK-861 Dose 3~TAK-861 Dose 4~Placebo (dummy inactive pill) - this is a tablet that looks like the study drug but has no active ingredient~This multi-center trial will be conducted worldwide. The overall time to participate in this study is up to 23 weeks. Participants will make multiple visits to the clinic during the treatment period and then will either enroll in a long-term extension study in which all participants will receive TAK-861 or have 2 final visits 7 and 28 days after last dose of study drug for follow-up assessments.
The main aim of this study is to see how TAK-861 works on symptoms of narcolepsy, including excessive daytime sleepiness and cataplexy. Approximately 100 participants will take part in the study across North America, Europe and Asia Pacific.~The treatment (TAK-861 or placebo) will be administered for 8 or 12 weeks. After this treatment period the participant will have the option to participate in a separate, long- term extension study during which all participants will be treated with TAK-861.