TAK-861 Study for Narcolepsy Type 1 aims to check how well TAK-861 works to reduce excessive daytime sleepiness (EDS) and sudden muscle weakness with consciousness (cataplexy) in people with narcolepsy type 1 (NT1). The study will include about 152 participants randomly divided into three groups: two different doses of TAK-861 and a placebo group. A placebo looks like the real drug but doesn't have any active ingredients. The study drug will be taken for 12 weeks, and the study will happen in many places around the world.

Eligibility: Participants must have a BMI between 18 to 40 kg/m², a diagnosis of NT1, and at least 4 episodes of cataplexy per week. They must also have specific genetic markers or low levels of a brain chemical called orexin/hypocretin-1.

• Study duration is 12 weeks.
• Global, multi-center trial.
• Randomized into three groups for treatment.