Dose-finding Study Assessing the Efficacy, Safety, and Pharmacokinetics of Daridorexant in Subjects Aged 10 to < 18 Years with Insomnia Disorder

Inclusion Criteria:

• Signed and dated informed consent form (ICF) from the caregiver, i.e., parent/legalguardian prior to any study mandated procedure, or as per local regulation.

• Written assent must be obtained from subjects of the appropriate age who can giveassent, as determined by the caregiver and local regulation or institutional reviewboards (IRBs) / independent ethics committees (IECs).

• Male or female subjects aged ≥ 10 and < 18 years at the time of signing the ICF.

• Chronic insomnia disorder in accordance with International Classification of SleepDisorders (ICSD), 3rd edition or insomnia disorder in accordance with DSM-5 criteriaat Screening, as supported by statements from the child and/or the caregiver:

1. Difficulty initiating or maintaining sleep, or early morning awakening withinability to return to sleep,

2. Sleep difficulty has been present for at least 3 months prior to Screening,

3. Sleep difficulty occurs at least 3 nights per week,

4. Persistence of sleep difficulty, despite adequate sleep hygiene ornon-pharmacological therapy,

5. The sleep problem occurs despite adequate age appropriate time and opportunityfor sleep,

6. The sleep problem is not due to the direct pharmacological effects of anyconcomitant medication (e.g., amphetamines, selective serotonin reuptakeinhibitors) as per investigator judgment,

7. Self-report or caregiver report of poor sleep quality and/or quantity impactingthe daytime performance of the subject,

• Sleep Disturbance Scale for Children (SDSC) score > 16 on the Difficulty Initiatingor Maintaining Sleep domain at Screening.

• Adolescent of Child-Bearing Potential (AoCBP):

1. Negative serum pregnancy test at Screening and a negative urine pregnancy testat Randomization.

2. Agreement to undertake urine pregnancy tests during the study, as per theschedule of activities and up to 5 days after study treatment discontinuation.

3. Agreement to use an acceptable effective method of contraception from Screeningup to 5 days after study treatment discontinuation.

• Inclusion criteria applicable only to a subset of children with insomnia andcomorbid neurodevelopmental disorder: Must have a documented history of NDD (including ASD or ADHD) according to DSM-5 criteria, as confirmed by review ofmedical records, at Screening. Use of CNS stimulants is allowed if started at least 4 weeks prior to Screening, stable and expected to remain stable during the studyuntil EOT. CNS stimulants are recommended to be taken in the morning.

Exclusion Criteria:

• Body weight < 25 kg.

• Daytime napping ≥ 1 h per day on at least 3 weekdays per week during the 3 monthsprior to Screening.

• Any lifetime history of sleep-related breathing disorders such as obstructive sleepapnea, based on the subject's medical records. Note: a subject whose breathingdisorder has been treated by tonsillectomy/ adenoidectomy remains eligible.

• Any other diagnosed sleep-wake disorder as defined in DSM-5 or ICSD-3 (e.g.,restless legs syndrome, circadian rhythm sleep wake disorder, parasomnias,narcolepsy) at Screening.

• Any of the following conditions related to suicidality:

1. Any suicidal ideation with intent, with or without a plan at Screening, i.e.,answering "Yes" to questions 4 or 5 on the suicidal ideation section of thelifetime (Visit 1) and visit (Visit 2) version of the C-SSRS©. Participants whoanswer "yes" to any of these questions must be referred to the investigator forfollow-up evaluation.

2. History of suicide attempt on the suicidal behavior section of the lifetimeversion of the C-SSRS© at Visit 1.

• Any acute or unstable significant medical condition (e.g., seizure disorder, bipolardisorder, schizophrenia), hematology/biochemistry test results, ECG resultsdeviating from the normal ranges to a clinically relevant extent that would precludeparticipation in the study or could prevent the subject from complying with studyrequirements, as per investigator judgement.

• Cognitive behavior therapy (CBT) for any indication is allowed only if it has beenstarted at least 1 month prior to Visit 2 and is kept stable throughout the study.