Inclusion Criteria:  1. Participant with a diagnosis of Narcolepsy Type 1 (NT1) who has completed TAK-994-1501 Part B before enrollment (which will occur immediately following the final TAK-994-1501 assessments), and for whom the investigator has no clinical objection they be enrolled.  Exclusion Criteria:  1. Participant has a clinically significant moderate or severe ongoing AE related to the study drug from the prior study.