A Study of TAK-861 in Participants With Narcolepsy Type 2

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.