Study to Assess the Efficacy and Safety of ACT-541468 (Daridorexant) in Adult and Elderly Subjects Suffering From Difficulties to Sleep

Inclusion Criteria: * Signed informed consent prior to any study-mandated procedure; * Male or female aged ≥ 18 years; * Insomnia disorder according to DSM-5 criteria; * Insomnia Severity Index score ≥ 15; * Insufficient sleep quantity as collected subjectively in the sleep diary and validated objectively by polysomnography; * Women of childbearing potential must have a negative and urine pregnancy test and use the contraception scheme up to at least 30 days after last study treatment intake. Exclusion Criteria: * Body mass index below 18.5 or above 40.0 kg/m2; * Any lifetime history of of related breathing disorder, periodic limb movement disorder, restless legs syndrome, circadian rhythm disorder, rapid eye movement (REM) behavior disorder, narcolepsy, or apnea/hypopnea; * Cognitive behavioral therapy (CBT) only allowed if, the treatment started at least 1 month prior to Visit 3 and the subject agrees to continue this CBT throughout the study; * Self-reported usual daytime napping ≥ 1 hour per day and ≥ 3 days per week; * Acute or unstable psychiatric conditions diagnosed by the Mini International Neuropsychiatric Interview; * Mini Mental State Examination (MMSE) score \< 25 in subjects ≥ 50 years; * For female subjects: pregnant, lactating or planning to become pregnant during projected duration of the study; * History or clinical evidence of any disease or medical condition or treatment, which may put the subject at risk of participation in the study or may interfere w…