This study tests a drug called TAK-861 for people with narcolepsy type 1 (NT1), a condition that causes daytime sleepiness and muscle weakness (cataplexy). The goal is to see if TAK-861 reduces sleepiness and cataplexy, and if it improves attention and quality of life. About 152 people will join and will be randomly put into one of three groups: two different doses of TAK-861 or a placebo (a pill with no medicine). The study will last for 12 weeks (about 3 months) and will be conducted in different places worldwide.

To join, you must be between a body mass index (BMI) of 18 and 40 and have NT1 diagnosed by a doctor. You need to have at least four episodes of cataplexy per week. Some medical conditions might prevent you from joining, like having a history of heart disease or cancer in the last 5 years.

• Study lasts 12 weeks with different doses or placebo.
• Participants should have NT1 and frequent cataplexy episodes.
• Excludes those with recent serious health conditions.