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

• ALKS 2680 Dose 1 (Drug), also known as Alixorexton: Participants will receive ALKS 2680 tablets, daily, orally, for 12 weeks
• ALKS 2680 Dose 2 (Drug), also known as Alixorexton: Participants will receive ALKS 2680 tablets, daily, orally, for 12 weeks
• Placebo (Drug): Participants will receive placebo tablets, daily, orally for 12 weeks

Primary outcomes

• Change in mean sleep latency (MSL) on Maintenance of Wakefulness Test (MWT) from baseline to Week 12 by dose level [Baseline to Week 12]

Secondary outcomes

• Change in Epworth Sleepiness Scale (ESS) from baseline to Week 12 by dose level [Baseline to Week 12]
• Weekly cataplexy rate (WCR) at Week 12 by dose level [Week 12]
• Percentage of participants who achieve a status of "none" or "mild" on Patient Global Impression- Severity (PGI-S) scale(general disease) at Week 12 by dose level [Week 12]
• Change in British Columbia Cognitive Complaints Inventory (BC-CCI) from baseline to Week 12 by dose level [Baseline to Week 12]
• Change in number of lapses on Psychomotor Vigilance Task (PVT) from baseline to Week 12 by dose level [Baseline to Week 12]
• Change in Patient-Reported Outcomes Measurement Information System - Fatigue 6a (PROMIS Fatigue 6a) from baselineto Week 12 by dose level [Baseline to Week 12]
• Percentage of participants who achieve a status of "normal, not ill at all", "borderline ill", or "mildly ill" on Clinical Global Impression-Severity (CGI-S) (general disease) at Week 12 by dose level [Week 12]
• Change in Narcolepsy Severity Scale for Clinical Trials (NSS-CT) from baseline to Week 12 by dose level [Baseline to Week 12]
• Incidence of treatment emergent adverse events [Baseline to Week 14]

Sex: All, ages: 18 Years to 70 Years

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.

• Medical Director, MD, Study director, Alkermes, Inc.