The purpose of this phase 3 study is to evaluate the efficacy and safety of Daridorexant compared to 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.