Suvorexant 20 mg + placebo matching suvorexant 40 mg for participants <65 years old; Suvorexant 15 mg + placebo matching suvorexant 30 mg for participants ≥65 years old; all study drug is tablet for oral administration, taken once daily at bedtime. Participants receive this dose during the 3-month TRT Phase and, if applicable, the optional 3-month EXT Phase. During the 1-week DB RO following the TRT/EXT phase, participants in this study arm receive the noted suvorexant dose or placebo, in a 1:1 ratio. During the 2-week single-blind Run-in period prior to randomization all participants receive placebo to suvorexant once daily at bedtime.

Matching placebos to suvorexant 40 mg and 20 mg for participants <65 years old; matching placebos to suvorexant 30 mg and 15 mg for participants ≥65 years old; all study drug is tablet for oral administration, taken once daily at bedtime. Placebo is a third treatment arm for comparison to the two active (suvorexant) treatment arms during the 3-month TRT Phase and, if applicable, the optional 3-month EXT Phase. During the 1-week DB RO following the TRT/EXT phase, participants in this study arm continue to receive placebo. During the 2-week single-blind Run-in period prior to randomization all participants receive placebo to suvorexant once daily at bedtime.

WASO is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of wakefulness from the onset of persistent sleep (i.e., 10 consecutive minutes of sleep) to the end of PSG assessment the following morning. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

sTSOm is the average over a defined day range of the participant's report of the duration of time that it took to fall asleep, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Month 1 range is Days 23-30 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

sTSOm is the average over a defined day range of the participant's report of the duration of time that it took to fall asleep, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Month 3 range is Days 76-90 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

LPS is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of time from the beginning of PSG assessment ("Lights-Off") to the first interval of 10 consecutive minutes of sleep. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

LPS is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of time from the beginning of PSG assessment ("Lights-Off") to the first interval of 10 consecutive minutes of sleep. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

An AE is any unfavorable and unintended change in the structure, function or chemistry of the body temporally associated with study drug administration, whether or not considered related to the study drug. Participants with an AE occurring during the initial 3-month DB TRT Phase are counted once in this summary.

An AE is any unfavorable and unintended change in the structure, function or chemistry of the body temporally associated with study drug administration, whether or not considered related to the study drug. Participants who discontinued study drug treatment due to an AE occurring during the initial 3-month DB TRT Phase are counted once in this summary.

sTSTm is the average over a defined day range of the participant's report of the total amount of time spent asleep before waking for the day, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Month 1 range is Days 23-30 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

sTSTm is the average over a defined day range of the participant's report of the total amount of time spent asleep before waking for the day, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Month 3 range is Days 76-90 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

WASO is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of wakefulness from the onset of persistent sleep (i.e., 10 consecutive minutes of sleep) to the end of PSG assessment the following morning. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

WASO is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of wakefulness from the onset of persistent sleep (i.e., 10 consecutive minutes of sleep) to the end of PSG assessment the following morning. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

WASO is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of wakefulness from the onset of persistent sleep (i.e., 10 consecutive minutes of sleep) to the end of PSG assessment the following morning. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

sTSOm is the average over a defined day range of the participant's report of the duration of time that it took to fall asleep, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Week 1 range is Days 2-8 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

sTSOm is the average over a defined day range of the participant's report of the duration of time that it took to fall asleep, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Month 1 range is Days 23-30 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

sTSOm is the average over a defined day range of the participant's report of the duration of time that it took to fall asleep, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Month 3 range is Days 76-90 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

LPS is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of time from the beginning of PSG assessment ("Lights-Off") to the first interval of 10 consecutive minutes of sleep. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

LPS is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of time from the beginning of PSG assessment ("Lights-Off") to the first interval of 10 consecutive minutes of sleep. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

LPS is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of time from the beginning of PSG assessment ("Lights-Off") to the first interval of 10 consecutive minutes of sleep. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

After a 2-week single-blind placebo Run-in, participants received placebo to suvorexant daily before bedtime during the 3-month DB TRT Phase.

Total of all reporting groups

N=252, 383, 384, 1019 for Suvorexant Low Dose, Suvorexant High Dose, Placebo and Total, respectively.

N=193, 291, 290, 774 for Suvorexant Low Dose, Suvorexant High Dose, Placebo and Total, respectively. WASO was assessed during sleep laboratory (polysomnography [PSG]) assessment, which was conducted in a subset of the study population.

N=252, 383, 384, 1019 for Suvorexant Low Dose, Suvorexant High Dose, Placebo and Total, respectively.

N=193, 291, 290, 774 for Suvorexant Low Dose, Suvorexant High Dose, Placebo and Total, respectively. LPS was assessed during sleep laboratory (PSG) assessment, which was conducted in a subset of the study population.

sTSTm is the average over a defined day range of the participant's report of the total amount of time spent asleep before waking for the day, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Month 3 range is Days 76-90 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

Randomized participants with ≥1 post-randomization e-diary observation after ≥1 dose of study drug, and baseline data were included in this analysis. The Primary hypothesis included only the suvorexant HD-placebo comparison.

WASO is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of wakefulness from the onset of persistent sleep (i.e., 10 consecutive minutes of sleep) to the end of PSG assessment the following morning. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

Randomized participants with ≥1 post-randomization PSG observation after ≥1 dose of study drug, and baseline data were included in this analysis. The Primary hypothesis included only the suvorexant HD-placebo comparison.

WASO is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of wakefulness from the onset of persistent sleep (i.e., 10 consecutive minutes of sleep) to the end of PSG assessment the following morning. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

Randomized participants with ≥1 post-randomization PSG observation after ≥1 dose of study drug, and baseline data were included in this analysis. The Primary hypothesis included only the suvorexant HD-placebo comparison.

sTSOm is the average over a defined day range of the participant's report of the duration of time that it took to fall asleep, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Month 1 range is Days 23-30 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

Randomized participants with ≥1 post-randomization e-diary observation after ≥1 dose of study drug, and baseline data were included in this analysis. The Primary hypothesis included only the suvorexant HD-placebo comparison.

sTSOm is the average over a defined day range of the participant's report of the duration of time that it took to fall asleep, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Month 3 range is Days 76-90 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

Randomized participants with ≥1 post-randomization e-diary observation after ≥1 dose of study drug, and baseline data were included in this analysis. The Primary hypothesis included only the suvorexant HD-placebo comparison.

LPS is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of time from the beginning of PSG assessment ("Lights-Off") to the first interval of 10 consecutive minutes of sleep. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

Randomized participants with ≥1 post-randomization PSG observation after ≥1 dose of study drug, and baseline data were included in this analysis. The Primary hypothesis included only the suvorexant HD-placebo comparison.

LPS is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of time from the beginning of PSG assessment ("Lights-Off") to the first interval of 10 consecutive minutes of sleep. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

Randomized participants with ≥1 post-randomization PSG observation after ≥1 dose of study drug, and baseline data were included in this analysis. The Primary hypothesis included only the suvorexant HD-placebo comparison.

sTSTm is the average over a defined day range of the participant's report of the total amount of time spent asleep before waking for the day, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Week 1 range is Days 2-8 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

Randomized participants with ≥1 post-randomization e-diary observation after ≥1 dose of study drug, and baseline data were included in this analysis.

sTSTm is the average over a defined day range of the participant's report of the total amount of time spent asleep before waking for the day, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Month 1 range is Days 23-30 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

Randomized participants with ≥1 post-randomization e-diary observation after ≥1 dose of study drug, and baseline data were included in this analysis. Only suvorexant LD-placebo comparison included, as suvorexant HD-placebo comparison is included in Primary hypothesis.

sTSTm is the average over a defined day range of the participant's report of the total amount of time spent asleep before waking for the day, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Month 3 range is Days 76-90 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

Randomized participants with ≥1 post-randomization e-diary observation after ≥1 dose of study drug, and baseline data were included in this analysis. Only suvorexant LD-placebo comparison included, as suvorexant HD-placebo comparison is included in Primary hypothesis.

WASO is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of wakefulness from the onset of persistent sleep (i.e., 10 consecutive minutes of sleep) to the end of PSG assessment the following morning. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

Randomized participants with ≥1 post-randomization PSG observation after ≥1 dose of study drug, and baseline data were included in this analysis.

WASO is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of wakefulness from the onset of persistent sleep (i.e., 10 consecutive minutes of sleep) to the end of PSG assessment the following morning. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

Randomized participants with ≥1 post-randomization PSG observation after ≥1 dose of study drug, and baseline data were included in this analysis. Only suvorexant LD-placebo comparison included, as suvorexant HD-placebo comparison is included in Primary hypothesis.

WASO is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of wakefulness from the onset of persistent sleep (i.e., 10 consecutive minutes of sleep) to the end of PSG assessment the following morning. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

Randomized participants with ≥1 post-randomization PSG observation after ≥1 dose of study drug, and baseline data were included in this analysis. Only suvorexant LD-placebo comparison included, as suvorexant HD-placebo comparison is included in Primary hypothesis.

sTSOm is the average over a defined day range of the participant's report of the duration of time that it took to fall asleep, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Week 1 range is Days 2-8 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

Randomized participants with ≥1 post-randomization e-diary observation after ≥1 dose of study drug, and baseline data were included in this analysis.

sTSOm is the average over a defined day range of the participant's report of the duration of time that it took to fall asleep, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Month 1 range is Days 23-30 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

Randomized participants with ≥1 post-randomization e-diary observation after ≥1 dose of study drug, and baseline data were included in this analysis. Only suvorexant LD-placebo comparison included, as suvorexant HD-placebo comparison is included in Primary hypothesis.

sTSOm is the average over a defined day range of the participant's report of the duration of time that it took to fall asleep, as recorded in a daily e-diary. Averages were derived by taking the mean of all available daily measurements (excluding the mornings following any PSG nights) falling within the day range; Month 3 range is Days 76-90 (Day 1 is day of first double-blind dose). A participant must have at least 3 days of data during the defined day range to calculate an average for the day range; otherwise, the mean value was considered missing for that day range. The baseline value is the mean of the last 7 daily measurements obtained during the placebo Run-in period.

Randomized participants with ≥1 post-randomization e-diary observation after ≥1 dose of study drug, and baseline data were included in this analysis. Only suvorexant LD-placebo comparison included, as suvorexant HD-placebo comparison is included in Primary hypothesis.

An AE is any unfavorable and unintended change in the structure, function or chemistry of the body temporally associated with study drug administration, whether or not considered related to the study drug. Participants with an AE occurring during the initial 3-month DB TRT Phase are counted once in this summary.

All Patients as Treated (APaT) population, consisting of all randomized participants who received at least one dose of study medication

An AE is any unfavorable and unintended change in the structure, function or chemistry of the body temporally associated with study drug administration, whether or not considered related to the study drug. Participants who discontinued study drug treatment due to an AE occurring during the initial 3-month DB TRT Phase are counted once in this summary.

All Patients as Treated (APaT) population, consisting of all randomized participants who received at least one dose of study medication

LPS is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of time from the beginning of PSG assessment ("Lights-Off") to the first interval of 10 consecutive minutes of sleep. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

Randomized participants with ≥1 post-randomization PSG observation after ≥1 dose of study drug, and baseline data were included in this analysis.

LPS is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of time from the beginning of PSG assessment ("Lights-Off") to the first interval of 10 consecutive minutes of sleep. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

Randomized participants with ≥1 post-randomization PSG observation after ≥1 dose of study drug, and baseline data were included in this analysis. Only suvorexant LD-placebo comparison included, as suvorexant HD-placebo comparison is included in Primary hypothesis.

LPS is measured during overnight sleep laboratory (PSG) assessments at baseline, Night 1, Month 1 and Month 3, and is defined as the duration of time from the beginning of PSG assessment ("Lights-Off") to the first interval of 10 consecutive minutes of sleep. Beginning of PSG assessment ("Lights-Off") is at approximately the participant's habitual bedtime. The participant is awakened, or allowed to get out of bed if already awake, after 8 hours of PSG recording ("Lights-On"). PSG assessments consist of electronic measurement of brain activity and eye and muscle movements. PSG data was scored by a Centralized PSG reading center.

Randomized participants with ≥1 post-randomization PSG observation after ≥1 dose of study drug, and baseline data were included in this analysis. Only suvorexant LD-placebo comparison included, as suvorexant HD-placebo comparison is included in Primary hypothesis.

After a 2-week single-blind placebo Run-in, participants received suvorexant HD (40 mg for participants aged 18 to <65 years; and 30 mg for participants aged ≥65 years) daily before bedtime during the 3-month DB TRT Phase.

After a 2-week single-blind placebo Run-in, participants received placebo to suvorexant daily before bedtime during the 3-month DB TRT Phase.

After receiving suvorexant LD during the 3-month DB TRT Phase, participants could continue on same dose during the optional 3-month DB EXT Phase.

After receiving suvorexant HD during the 3-month DB TRT Phase, participants could continue on same dose during the optional 3-month DB EXT Phase.

After receiving placebo to suvorexant during the 3-month DB TRT Phase, participants could continue on placebo to suvorexant during the optional 3-month DB EXT Phase.

After receiving suvorexant LD during the 3-Month DB TRT Phase, and for some participants, the optional 3-Month DB EXT Phase, participants received their same dose of suvorexant during a 1-week DB RO Phase.

After receiving suvorexant LD during the 3-Month DB TRT Phase, and for some participants, the optional 3-Month DB EXT Phase, participants received placebo to suvorexant during a 1-week DB RO Phase.

After receiving suvorexant HD during the 3-Month DB TRT Phase, and for some participants, the optional 3-Month DB EXT Phase, participants received their same dose of suvorexant during a 1-week DB RO Phase.

After receiving suvorexant HD during the 3-Month DB TRT Phase, and for some participants, the optional 3-Month DB EXT Phase, participants received placebo to suvorexant during a 1-week DB RO Phase.

After receiving placebo to suvorexant during the 3-Month DB TRT Phase, and for some participants, the optional 3-Month DB EXT Phase, participants received placebo to suvorexant during a 1-week DB RO Phase.

During 14-day Follow-up after last dose no study drug was administered. Follow-up AE data is presented for TRT/EXT participants who entered Follow-up directly from TRT or EXT Phase and had received suvorexant LD during TRT/EXT Phase.

During 14-day Follow-up after last dose no study drug was administered. Follow-up AE data is presented for TRT/EXT participants who entered Follow-up directly from TRT or EXT Phase and had received suvorexant HD during TRT/EXT Phase.

During 14-day Follow-up after last dose no study drug was administered. Follow-up AE data is presented for TRT/EXT participants who entered Follow-up directly from TRT or EXT Phase and had received placebo during TRT/EXT Phase.

During 14-day Follow-up after last dose no study drug was administered. Follow-up AE data is presented for RO participants who entered Follow-up from RO Phase, and had received suvorexant LD during TRT/EXT and RO Phases.

During 14-day Follow-up after last dose no study drug was administered. Follow-up AE data is presented for RO participants who entered Follow-up from RO Phase, and had received suvorexant LD during TRT/EXT Phase and placebo during RO Phase.

During 14-day Follow-up after last dose no study drug was administered. Follow-up AE data is presented for RO participants who entered Follow-up from RO Phase, and had received suvorexant HD during TRT/EXT and RO Phases.

During 14-day Follow-up after last dose no study drug was administered. Follow-up AE data is presented for RO participants who entered Follow-up from RO Phase, and had received suvorexant HD during TRT/EXT Phase and placebo during RO Phase.

During 14-day Follow-up after last dose no study drug was administered. Follow-up AE data is presented for RO participants who entered Follow-up from RO Phase, and had received placebo during TRT/EXT and RO Phases.