Study to Assess the Efficacy and Safety of ACT-541468 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 with the
study assessments.

- Any circumstances or conditions, which, in the opinion of the investigator, may affect
the subject's full participation in the study or compliance with the protocol.