A Study to Evaluate the Efficacy, Safety and Tolerability of ALKS 2680 in Adults With Narcolepsy Type 1 (Brilliance NT1 - 304)

The purpose of this study is to measure decreases in daytime sleepiness, cataplexy (sudden loss of muscle tone), and disease symptoms in participants with NT1 when taking ALKS 2680 tablets compared with placebo tablets.

Inclusion Criteria: * Meets the diagnostic criteria of NT1 according to ICSD-3-TR guidelines, confirmed by diagnostic evaluations (either PSG/MSLT\* or CSF hypocretin-1 level) Exclusion Criteria: * Has another comorbid sleep disorder or condition that may influence the sleep-wake cycle. * Has a history or presence at Visit 1 of other clinically significant (treated or untreated) illness, disease, abnormality, or surgical procedure that, in the opinion of the Investigator, might compromise participant safety, interfere with any study assessment, or affect the participant's ability to complete the study. * Is currently enrolled in another interventional clinical trial or has received any investigational drug or used any interventional investigational device within 30 days prior to Visit 1. Participants previously enrolled in Study ALKS 2680-201 are not eligible for enrollment. * Is currently pregnant, breastfeeding, or is planning to become pregnant during the study.