Long-term Study of Lemborexant in Insomnia Disorder (SUNRISE 2)

Inclusion Criteria

• Male or female, age 18 years or older at the time of informed consent
• Meets the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM 5) criteria for Insomnia Disorder, as follows:
• Complains of dissatisfaction with nighttime sleep in the form of difficulty getting to sleep, difficulty staying asleep, and/or awakening earlier in the morning than desired despite adequate opportunity for sleep
• Frequency of complaint ≥3 times per week
• Duration of complaint ≥3 months
• Associated with complaint of daytime impairment
• History of (Subjective Sleep Onset Latency) sSOL ≥30 minutes on at least 3 nights per week in the previous 4 weeks and/or subjective Wake after Sleep Onset (sWASO) ≥60 minutes on at least 3 nights per week in the previous 4 weeks
• History of regular time spent in bed, either sleeping or trying to sleep, between 7 and 9 hours
• Regular bedtime, between 21:00 and 01:00 and regular wake time, the time the participant gets out of bed for the day, between 05:00 and 10:00
• Insomnia Severity Index (ISI) score ≥15
• Confirmation of current insomnia symptoms as determined from the Sleep Diary completed on at least 7 consecutive mornings (minimum 5 of 7 for eligibility), such that sSOL ≥30 minutes on at least 3 of the 7 nights and/or sWASO ≥60 minutes on at least 3 of the 7 nights
• Confirmation of time spent in bed, as determined from on the Sleep Diary completed on 7 mornings between the first and second screening visit, such that there are not more than 2 nights with duration of time spent in bed 7 hours and 10 hours
• Confirmation of regular bedtimes and wake times such that the participant has a regular time spent in bed, either sleeping or trying to sleep, between 7 and 10 hours for the final 7 nights of the before visit 3.
• Confirmation of regular bedtime between 21: 00 and 01:00 and time of getting out of bed for the day between 05:00 and 10:00 for the final 7 nights of the before visit 3.
• Willing and able to comply with all aspects of the protocol, including staying in bed for at least 7 hours each night
• Willing to not start a behavioral or other treatment program for insomnia during the participants participation in the study

Exclusion Criteria

• A current diagnosis of sleep-related breathing disorder, periodic limb movement disorder, restless legs syndrome, circadian rhythm sleep disorder, or an exclusionary score on screening instruments to rule out individuals with symptoms of certain sleep disorders other than insomnia.
• STOPBang score greater than or equal to (>=) 5
• International Restless Legs Scale (IRLS) score >=16
• Epworth Sleepiness Scale (ESS) score >15
• Reports symptoms potentially related to narcolepsy that in the clinical opinion of the investigator indicates the need for referral for a diagnostic evaluation for the presence of narcolepsy
• Reports a history of sleep-related violent behavior, or sleep driving, or any other complex sleep-related behavior, eg, making phone calls, or preparing and eating food while asleep
• For participants who underwent polysomnography (PSG) within the previous year:
• Age 18 to 64 years: Apnea Hypopnea Index ≥10, or Periodic Limb Movements with Arousal Index ≥10
• Age ≥65 years: Apnea Hypopnea Index >15, or Periodic Limb Movements with Arousal Index >15
• Beck Depression Inventory - II (BDI II) score >19 at Screening
• Beck Anxiety Inventory (BAI) score >15 at Screening
• Habitually naps more than 3 times per week
• Females who are breastfeeding or pregnant at Screening or Study Baseline
• Females of childbearing potential who are not practicing acceptable pregnancy prevention methods (NOTE: All females will be considered to be of childbearing potential unless they are postmenopausal or have been sterilized surgically.)
• Excessive caffeine use that in the opinion of the investigator contributes to the participant's insomnia, or habitually consumes caffeine-containing beverages after 18:00 and is unwilling