['insomnia disorder']
['lemborexant', 'placebo']

        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 to forego caffeine after 18:00 for the duration of his/her
             participation in the study

          -  History of drug or alcohol dependency or abuse within approximately the previous 2
             years

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

          -  A prolonged QT/QT interval corrected by Fridericia's formula (QTcF >450 ms) as
             demonstrated by a repeated electro cardiogram(ECG) at Screening (repeated only if
             initial ECG indicates a QTcF interval >450 ms)

          -  Current evidence of clinically significant disease (e.g., cardiac, respiratory,
             gastrointestinal, renal, neurological [including participants who lack capacity and/or
             whose cognitive decline indicates disorientation to person/place/time and/or
             situation], or psychiatric disease or malignancy other than basal cell carcinoma) or
             chronic pain that in the opinion of the investigator(s) could affect the participant's
             safety or interfere with the study assessments

          -  Comorbid nocturia resulting in frequent need to get out of bed to use the bathroom
             during the night

          -  Scheduled for major surgery during the study

          -  Used any prohibited prescription or over-the-counter concomitant medications within 1
             week before the first dose of study medication

          -  Used any modality of treatment for insomnia, including cognitive behavioral therapy or
             marijuana within 2 weeks before Screening

          -  Failed treatment with suvorexant (Belsomra®) (efficacy and/or safety) following
             treatment with an appropriate dose and of adequate duration in the opinion of the
             investigator

          -  Transmeridian travel across more than 3 time zones in the 2 weeks before Screening, or
             between Screening and Study Baseline

          -  Previously participated in any clinical trial of lemborexant
      