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

Inclusion Criteria:

1. Korean male or female, age 19 to 80 years, at the time of informed consent

2. 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 difficultygetting to sleep with or without difficulty staying asleep and/or awakeningearlier 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

3. Subjective Sleep Onset Latency (sSOL) typically >= 30 minutes on at least 3 nightsper week in the previous 4 weeks at Screening

4. Insomnia Severity Index (ISI) score >=13 at Screening

5. Regular time in bed between 6.5 and 9.0 hours at Screening

6. At 2nd Screening Visit (Visit 2): Confirmation (via Sleep Diary) of a regularbedtime, 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 timethe participant gets out of bed for the day, between 05:00 and 09:00 on at least 5of the final 7 nights.

7. Confirmation of current insomnia symptoms, as determined from responses on the sleepdiary 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

8. Confirmation of sufficient duration of time spent in bed, as determined fromresponses on the sleep diary on the 7 most recent mornings before the 2nd ScreeningVisit (Visit 2), such that there are no more than 2 nights with time spent in bedduration less than (<) 7 hours or greater than (>) 10 hours

9. During Run-in period, objective (PSG) evidence of insomnia as follows:

• SE less than or equal to (<=) 85 percent (%); and

• LPS >= 30 minutes

10. Provide written informed consent

11. Willing and able to comply with all aspects of the protocol, including staying inbed for at least 7 hours each night

Exclusion Criteria:

1. Females who are breastfeeding or pregnant at Screening or Baseline (as documented bya positive beta-human chorionic gonadotropin (beta-hCG). A separate baselineassessment is required if a negative screening pregnancy test was obtained more than 72 hours before the 1st dose of study drug

2. Females of childbearing potential who:

• Within 28 days before study entry, did not use a highly effective method ofcontraception, 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 thesame oral contraceptive product for at least 28 days before dosing andmust agree to stay on the same dose of the oral contraceptive throughoutthe 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 describedabove) throughout the entire study period and for 28 days after study drugdiscontinuation. It is permissible that if a highly effective method ofcontraception is not appropriate or acceptable to the participant, then theparticipant must agree to use a medically acceptable method of contraception,that is, double-barrier methods of contraception such as latex or syntheticcondom plus diaphragm or cervical/vault cap with spermicide NOTE: All femaleswill be considered to be of childbearing potential unless they arepostmenopausal (amenorrheic for at least 12 consecutive months, in theappropriate age group, and without other known or suspected cause) or have beensterilized surgically (that is, bilateral tubal ligation, total hysterectomy,or bilateral oophorectomy, all with surgery at least 1 month before dosing)

3. Any history of a medical or psychiatric condition that in the opinion of theinvestigator(s) could affect the participants safety or interfere with the studyassessments

4. A prolonged QT interval corrected for heart rate by Fridericia's formula (QTcF)interval (QTcF >450 millisecond [ms]) as demonstrated by a repeated ECG. A historyof risk factors for torsade de pointes (example, heart failure, hypokalemia, familyhistory of long QT Syndrome) or the use of concomitant medications that prolongedthe QTcF interval

5. Any suicidal ideation with intent with or without a plan at Screening or within 6months of Screening

6. Any lifetime suicidal behavior

7. Evidence of clinically significant disease (example, cardiac; respiratory includingchronic obstructive pulmonary disease, acute and/or severe respiratory depression;gastrointestinal; moderate and severe hepatic impairment; renal including severerenal impairment; neurological including myasthenia gravis; psychiatric disease; ormalignancy within the past 5 years other than adequately treated basal cellcarcinoma) or chronic pain that in the opinion of the investigator(s) could affectthe participants safety or interfere with the study assessments. Participants forwhom a sedating drug would be contraindicated for safety reasons because of theparticipants occupation or activities

8. Hypersensitivity to lemborexant or to their excipients

9. Scheduled for surgery during the study that requires general anesthesia oradministration of prohibited medications

10. Known to be human immunodeficiency virus (HIV) positive

11. Active viral hepatitis (B or C) as demonstrated by positive serology

12. History of drug or alcohol dependency or abuse within approximately the last 2 years

13. A current diagnosis of sleep-related breathing disorder including obstructive sleepapnea (with or without continuous positive airway pressure [CPAP] treatment),periodic limb movement disorder, restless legs syndrome, circadian rhythm sleepdisorder, or narcolepsy, or an exclusionary score on screening instruments to ruleout individuals with symptoms of certain sleep disorders other than insomnia asfollows:

• STOPBang score >=5

• International Restless Legs Scale (IRLS) >=16

14. Apnea-Hypopnea Index >15 or Periodic Limb Movement with Arousal Index >15 asmeasured on the PSG at the 2nd Screening Visit

15. Reports symptoms potentially related to narcolepsy, that in the clinical opinion ofthe investigator indicates the need for referral for a diagnostic evaluation for thepresence of narcolepsy

16. Reports a history of sleep-related violent behavior, or sleep driving, or any othercomplex sleep-related behavior (example, making phone calls or preparing and eatingfood while sleeping)

17. For participants who underwent diagnostic PSG within 1 year before informed consent:

• Age 19 to 64 years: Apnea hypopnea Index >=10, or Periodic Limb Movements withArousal Index >=10,

• Age >=65 years: Apnea Hypopnea Index >15, or Periodic Limb Movements withArousal Index >15

18. Beck Depression Inventory-II (BDI-II) score >19 at Screening

19. Beck Anxiety Inventory (BAI) score >15 at Screening

20. Habitually naps during the day more than 3 times per week

21. Excessive caffeine use that in the opinion of the investigator contributes to theparticipants insomnia, or habitually consumes caffeine containing beverages after 18:00 and is unwilling to forego caffeine after 18:00 for the duration of his/herparticipation in the study. Participants are excluded if, in the previous 3 months,they had symptoms that would meet DSM-5 criteria for caffeine intoxication, whichincludes consumption of a high dose of caffeine (significantly in excess of 250 mg)and >=5 of the following symptoms: restlessness, nervousness, excitement, insomnia,flushed face, diuresis, gastrointestinal disturbance, muscle twitching, ramblingflow of thought and speech, tachycardia or cardiac arrhythmia, periods of highenergy, or psychomotor agitation. To be exclusionary, those symptoms must causedistress or impairment in social, occupational and other forms of functioning, andnot be associated with other substance, mental disorder or medical condition

22. Reports habitually consuming more than 14 drinks containing alcohol per week (females) or more than 21 drinks containing alcohol per week (males), or unwillingto limit alcohol intake to no more than 2 drinks per day or forego having alcoholwithin the 3 hours before bedtime for the duration of his/her participation in thestudy

23. Comorbid nocturia that is causing or exacerbating the insomnia

24. Used any prohibited prescription or over-the-counter concomitant medications within 1 week or 5 half-lives, whichever is longer, before the 1st dose of study medication (Run-in Period)

25. Used any modality of treatment for insomnia, including cognitive behavioral therapyor marijuana within 1 week or 5 half-lives, whichever is longer, before the 1st doseof study medication (Run-in Period)

26. Failed treatment with dual orexin receptor antagonist drugs (efficacy and/or safety)following treatment with an appropriate dose and of adequate duration in the opinionof the investigator

27. Transmeridian travel across more than 3 time zones in the 2 weeks before Screening,or between Screening and Baseline, or plans to travel across different time zonesduring the study

28. Performed shift work in the 2 weeks before Screening, or between Screening andBaseline, or plans to do during the study

29. A positive drug test at Screening, Run-in, or Baseline, or unwilling to refrain fromuse of recreational drugs during the study

30. Currently enrolled in another clinical trial or used any investigational drug ordevice within 30 days or 5* the half-life, whichever is longer, preceding informedconsent

31. Previously participated in any clinical trial of lemborexant