Delayed sleep phase syndrome (DSPS) is a disorder in which a person's sleep is delayed by two hours or more beyond what is considered an acceptable or conventional bedtime. The delayed sleep then causes difficulty in being able to wake up at the desired time.~In DSPS, bedtime is shifted later than the general population such that individuals have difficulty getting enough sleep to meet their sleep needs before they have to get up for their daytime obligations (work, school, childcare, etc.). As a result, patients experience daytime impairment, including daytime sleepiness and cognitive impairment. DSPS, if maintained in adulthood, is associated with numerous deleterious health effects, although causality is not well established. Two phenotypes of DSPS are recognized depending on the phase of entrainment: one with a late phase and normal phase angle (non-circadian) and other with a late phase and abnormal phase angle (circadian). The differentiation of these two phenotypes is theoretical: a mixed situation may be involved in some cases and the exact pathophysiology of each subtype is still controversial.~In theory, however, separating the sample into these two subtypes is likely important to predict short- and long-term responses to orexin antagonists in DSPS.~Lemborexant is one of the dual orexin receptor antagonists on the US market. The purpose of this study is to examine if lemborexant administered 5 to 10 mg nightly, taken at desired bedtime (at least 2 hours prior to self-reported sleep onset time), can improve the symptoms of Delayed Sleep Phase Syndrome both in the circadian and non-circadian phenotypes. The phenotypes will be recruited in 1:1 proportion.The effect of lemborexant will be analyzed based on the collection of information from actigraphy watches, sleep diaries, and sleep scales. The total participation time involved in this study will be approximately 6 weeks (2 weeks of baseline assessment followed by 2-weeks of treatment/placebo, and 2 weeks post-treatment).
The purpose of the study is to evaluate whether Lemborexant is more effective than placebo in shortening sleep onset latency in patients with delayed sleep phase syndrome (both type 1 and type 2). This will be tracked using sleep logs as well as actigraphy.~In this 2-year study, we will examine if Lemborexant administered 5-10 mg nightly taken at desired bedtime (at least 2 hours prior to self-reported sleep onset habitual time) can improve the symptoms of Delayed Sleep Phase Syndrome.