A Study to Assess the Pharmacodynamics of Lemborexant in Korean Participants With Insomnia Disorder

Inclusion Criteria

• Korean male or female, age 19 to 80 years, at the time of informed consent
• Meets the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) criteria for Insomnia Disorder, as follows:
• Complains of dissatisfaction with nighttime sleep, in the form of difficulty getting to sleep with or without difficulty staying asleep and/or awakening earlier in the morning than desired despite adequate opportunity for sleep
• Frequency of complaint greater than or equal to (>=) 3 times per week
• Duration of complaint >= 3 months
• Associated with complaint of daytime impairment
• Subjective Sleep Onset Latency (sSOL) typically >= 30 minutes on at least 3 nights per week in the previous 4 weeks at Screening
• Insomnia Severity Index (ISI) score >=13 at Screening
• Regular time in bed between 6.5 and 9.0 hours at Screening
• At 2nd Screening Visit (Visit 2): Confirmation (via Sleep Diary) of a regular bedtime, defined as the time the participant attempts to sleep, between 21:00 and 24:00 on at least 5 of the final 7 nights and regular waketime, defined as the time the participant gets out of bed for the day, between 05:00 and 09:00 on at least 5 of the final 7 nights.
• Confirmation of current insomnia symptoms, as determined from responses on the sleep diary on the 7 most recent mornings before the PSG during Screening Period (Visit 2), such that sSOL >=30 minutes on at least 3 of the 7 nights
• Confirmation of sufficient duration of time spent in bed, as determined from responses on the sleep diary on the 7 most recent mornings before the 2nd Screening Visit (Visit 2), such that there are no more than 2 nights with time spent in bed duration less than ( ) 10 hours
• During Run-in period, objective (PSG) evidence of insomnia as follows:
• SE less than or equal to ( = 30 minutes
• Provide written informed consent
• Willing and able to comply with all aspects of the protocol, including staying in bed for at least 7 hours each night

Exclusion Criteria

• Females who are breastfeeding or pregnant at Screening or Baseline (as documented by a positive beta-human chorionic gonadotropin (beta-hCG). A separate baseline assessment is required if a negative screening pregnancy test was obtained more than 72 hours before the 1st dose of study drug
• Females of childbearing potential who:
• Within 28 days before study entry, did not use a highly effective method of contraception, which includes any of the following:
• total abstinence (if it is their preferred and usual lifestyle)
• an intrauterine device or intrauterine hormone-releasing system (IUS)
• a contraceptive implant
• an oral contraceptive (Participant must have been on a stable dose of the same oral contraceptive product for at least 28 days before dosing and must agree to stay on the same dose of the oral contraceptive throughout the study and for 28 days after study drug discontinuation.)
• have a vasectomized partner with confirmed azoospermia
• Do not agree to use a highly effective method of contraception (as described above) throughout the entire study period and for 28 days after study drug discontinuation. It is permissible that if a highly effective method of contraception is not appropriate or acceptable to the participant, then the participant must agree to use a medically acceptable method of contraception, that is, double-barrier methods of contraception such as latex or synthetic condom plus diaphragm or cervical/vault cap with spermicide NOTE: All females will be considered to be of childbearing potential unless they are postmenopausal (amenorrheic for at least 12 consecutive months, in the appropriate age group, and without other known or suspected cause) or have been sterilized surgically (that is, bilateral tubal ligation, total hysterectomy, or bilateral oophorectomy, all with surgery at least 1 month before dosing)
• Any history of a medical or psychiatric condition that in the opinion of the investigator(