A Study of TAK-994 in Adults With Narcolepsy

The drug being tested in the study is called TAK-994. TAK-994, is being tested to treat participants with NT1. Participants who completed Part B of TAK-994-1501(NCT04096560) will be eligible for enrollment in this study. This study will enroll approximately 112 patients to receive one of three different TAK 994 dose for 8 weeks (active drug extension period). Participants will be randomly assigned to one of these different TAK 994 doses which will remain undisclosed to the participant and study doctor during the study (unless there is an urgent medical need). Following the 8-week Active Drug Extension Period, participants will continue into a 4-week Double-blind Randomized Withdrawal Period and will receive TAK-994 or Placebo. Participants randomized to TAK-994 will continue to receive the same dose as before. This multi-center trial will be conducted worldwide. The duration of treatment in this study is 12 weeks plus a 2 week safety follow up period. Participants will visit the clinic 10 times after the first dosing.