A Study to Evaluate the Efficacy and Safety of Daridorexant in Participants With Insomnia Disorder

Inclusion Criteria: * Signed informed consent prior to any study-mandated procedure; * Male or female aged ≥ 19 years; * Insomnia disorder according to DSM-5 criteria; * The predominant complaint is dissatisfaction with sleep quantity or quality, associated with one (or more) of the following symptoms: * Difficulty initiating sleep. * Difficulty maintaining sleep (characterized by frequent awakenings or problems returning to sleep after awakenings). * Early-morning awakening with inability to return to sleep. * Insomnia Severity Index score ≥ 15; * Insufficient sleep quantity as collected subjectively in the sleep diary A. ≥ 30 min to fall asleep, and B. Wake time during sleep ≥ 30 min, and C. Subjective Total Sleep Time (sTST) ≤ 6.5 h Exclusion Criteria: * Body mass index (BMI) ≥ 40.0 kg/m2 * Documented medical history and/or comorbidity of sleep-related breathing disorder * History of and/or concurrent sleep apnea or suspected sleep apnea * Korean-Mini Mental State Examination-2 (K-MMSE-2) score \< 25 in subjects ≥ 50 years; * For female subjects: pregnant, lactating or childbearing potential who do not consent to true abstinence or use an effective method of contraception for required period * Initiation of the cognitive behavior therapy (CBT) for treatment of insomnia disorder within 4 weeks prior to the Screening visit (Visit 1) or planned CBT during the study * A history of moderate to severe hepatic impairment (eg, Child-Pugh Class B or C) * Positive urine drug test or presence of alcohol in exhaled breath as detected by breathalyzer test.