Inclusion criteria:
Participants will meet the following
* Outpatients between 13 and 17 years of age at time of consent
* Diagnostic and Statistical Manual, 5th edition (DSM-5) criteria for Autism Spectrum Disorder (ASD) on the basis of clinical evaluation, confirmed with the Autism Diagnostic Interview-Revised (ADI-R) and the Autism Diagnostic Observation Schedule, 2nd Ed (ADOS-2) or the Childhood Autism Rating Scale, Second Edition (CARS-2)
* Males and females
* Availability of polysomnography (PSG) and/or actigraphy data
* Sleep disturbances as assessed using Children's Sleep Habits Questionnaire (CSHQ) with a score of 41 or higher and sleep efficiency of 85% or less and/or total sleep time less than 7 hours and/or wake after sleep onset of more than 30 minutes as measured by polysomnography (PSG) or actigraphy
* care provider who can reliably bring participant to clinic visits, provide trustworthy ratings, and interacts with participant on a regular basis
* stable medications for at least 2 weeks, with the exception of Prozac which is required to be stable for at least 4 weeks
* no planned changes in psychosocial and biomedical interventions during the trial
* willingness to provide additional saliva samples and participate in key study procedures (i.e., safety measurements every visit, PSG at weeks 4 and 8, and wear the actigraphy watch for 2 weeks before the beginning of trial as well as during the 8 weeks of the trial).
* requirement of dual protection contraception use in females who are sexually active and are of childbearing potential. Dual use contraceptive methods involve the use of both a hormonal method (oral contraceptives, long-acting reversible contraceptives, etc.) and a barrier method (condoms).
Exclusion criteria:
Participants will be excluded if one or more of the following is met
* active suicidal ideation or DSM-5 diagnosis of severe depression, substance use disorder, schizophrenia, schizoaffective disorder, or psychotic disorder
* unstable medical problems: migraine, asthma, seizure disorder, significant physical illness (e.g., anaphylaxis, serious liver, renal, or cardiac pathology), obstructive sleep apnea and severe hepatic insufficiency
* evidence of a metabolic, or infectious etiology for the participant's autism on the basis of medical history, neurologic history, and available tests for inborn errors of metabolism
* pregnant or sexually active females not using a reliable method of contraception (urinary tests for pregnancy will be employed in this study)
* Benzodiazepines, antiepileptic medications when prescribe for seizure disorder/epilepsy, melatonin and centrally-acting antihistamines
* history of hypersensitivity to suvorexant
* history of severe side effects from suvorexant
* history of adequate trial of suvorexant
* current use of any medications known to interact with suvorexant such as medications inhibiting CYP3A
* history of narcolepsy
