Study of Lemborexant for Irregular Sleep-Wake Rhythm Disorder and Mild to Moderate Alzheimer's Disease Dementia

This study will be conducted to determine the dose response of lemborexant (LEM) on the change from baseline in actigraphy-derived sleep-related parameters, wake-related parameters, and circadian-rhythm related parameters. Following the eligibility screening period, eligible participants will be assigned at random to 1 of 4 doses of LEM or to placebo for 4 weeks. After a 2-week follow-up period, eligible participants may enter an open-label extension period for up to 30 months or until the program discontinuation.