A Study to Evaluate Safety, and Efficacy of SUVN-G3031 (Samelisant) in Patients With Narcolepsy With and Without Cataplexy

Inclusion Criteria: * Ages of 18 to 65 years (adult), inclusive. * Have narcolepsy with or without cataplexy (Na-1 or Na-2) based on the International Classification of Sleep Disorders (3rd edition) criteria (new or previously diagnosed). * Have undergone a multiple sleep latency test (MSLT) study showing an MSLT of ≤ 8 minutes. * An Epworth Sleepiness Scale (ESS) score of ≥ 12; and mean Maintenance of Wakefulness Test (MWT) time of \< 12 min. * Body mass index ranging from 18 to \< 45 kg/m2 * Negative urine drug screen. * A woman must be either not of childbearing potential or of childbearing potential practicing highly effective methods of birth control. * Willingness to complete the study protocol with full compliance with procedures and sign an informed consent form (ICF). Exclusion Criteria: * Habitual wake-up time after 8 AM as assessed by sleep diary, habitual sleep time of \< 6 hours, and habitual bedtime past 1 AM as determined by sleep diary entries. * Use of any investigational therapy within the 30-day period prior to enrollment. * Excessive caffeine (defined as \> 600 mg/per day) use at least 1 week prior to baseline assessments and during the course of the trial. * Nicotine dependence that has an effect on sleep (eg, a patient who routinely awakens at night to smoke). * Use of concurrent medications prescribed to treat narcolepsy as specified including stimulants, antidepressants and sodium oxybate. * Current diagnosis of or past treatment for syndromes known to cause sleep disruption or any other cause of daytime sleepiness. * Clinically significant ECG abnormalities. * An occupation requiring variable shift work, night shifts, or frequent overnight travel which disrupts sleep patterns.