Narcolepsy With Cataplexy

The main aim of this study is to assess how effective TAK-861 is for treating narcolepsy type 1 and if this effect is maintained over time. Participants will take TAK-861 for a few months and if they meet certain criteria, they will be randomly assigned (by chance, like flipping a coin) to continue taking TAK-861 or take placebo (fake medicine) for up to 4 weeks to see if their narcolepsy symptoms return.

The purpose of this clinical trial is learn whether a behavioral (non-medication) treatment can reduce nightmares in adults with narcolepsy. All participants will receive the treatment and will complete three assessments. Half of the participants will receive the treatment after the first assessment, and half will receive it after the second assessment. Romantic partners of participants with narcolepsy will also be eligible to enroll in the study. Partners will complete three assessments but will not participate in the treatment.