The primary aims of this study is to contrast the effectiveness of CBT-I and pharmacotherapy (lemborexant) compared to placebo on sleep and mental health outcomes in people with insomnia disorder and anxiety/depressive symptoms. In addition, the study will evaluate whether insomnia phenotypes (i.e., +/- 6hrs of sleep) at baseline moderate the effectiveness of the intervention on both sleep and mental health outcomes.

Participants meeting study criteria will be randomized to one of three conditions (1:1:1) involving a 8-week treatment protocol (6 consultations over an 8-week period): 1) CBT-I, 2) an active hypnotic medication (lemborexant, 5-10 mg at bedtime) or 3) a placebo medication. A stratified-based variable block randomization schedule will be used to assign eligible patients to study arms once they have completed baseline measures. Stratification will be based on objective (EEG-defined) sleep duration (< 6 h vs. > 6 h) and age (< 50 years old vs. > 50 years old).

CBT-I will be provided in six therapy sessions provided over an 8-week period by trained graduate therapists in clinical psychology. Lemborexant and placebo medication (compounded and coded by a pharmacy) will be provided by consulting physicians (blinded) in six consultations over an 8-week period. Physicians will have the option of increasing the initial starting dose from 5 mg to 10 mg if needed. Control participants will receive a placebo medication identical in size and color to the active medication.

The assessment phase will include baseline, post-treatment, and 6-month follow-up.

Inclusion Criteria:

• 18 years of age or older at the time of enrolment
• Meeting Diagnostic and Statistical Manual of Mental Disorders (DSM-5) criteria for insomnia disorder (Duke Sleep Interview), with total Insomnia Severity Index (ISI) score > 10, and score ≥ 2 on either the interference or distress item
• Minimal symptoms of anxiety and/or depression with Patient Health Questionnaire (PHQ-9) > 4 and/or Generalized Anxiety Disorder (GAD-7) > 4
• Ability to read and understand French or English
• Ability to use a smartphone, tablet, or computer, and access to home internet connection

Exclusion Criteria:

• Presence of a lifetime diagnosis of any psychotic or bipolar disorder
• Untreated psychiatric disorder (e.g., major depression) or risk for suicide
• Substance/alcohol use disorder within the past year
• Any life-threatening or progressive medical illness (e.g., cancer, chronic obstructive pulmonary disease) or neurological degenerative disease (e.g., dementia)
• Current use of sleep-promoting medications (prescribed or over-the-counter) or cannabis-derived products for sleep more than two nights per week
• Current use of tricyclic antidepressants, monoamine oxidase inhibitors, or atypical antidepressants
• Reported diagnosis of sleep disorder other than insomnia (e.g., obstructive sleep apnea, restless legs syndrome, rapid eye movement behavior disorder, delayed phase sleep disorder, narcolepsy)
• Total score > 5 on the Stop-Bang Questionnaire and/or clinical symptoms suggestive of sleep apnea (excessive daytime sleepiness), or Epworth score > 10, restless legs syndrome or other signs of other sleep disorders
• Atypical sleep schedules (i.e., habitual bedtimes later than 2:00 AM and rising times later than 10:00 AM on more than two days/nights per week as documented from a sleep diary)
• Working night shifts more than five nights per month in the last six months
• Consuming 2 or more alcoholic beverages per day regularly (3 days or more per week)
• Any contra-indications to using the study medication, including lung disease/breathing problems (e.g., chronic obstructive pulmonary disease), use of strong or moderate CYP3A inducers (strong - rifampin, carbamazepine, and St. John's Wort) (moderate - bosentan, efavirenz, etravirine, and modafinil), pregnant and breastfeeding women
• Not using any method of birth control

Participants assigned to the medication groups (active and placebo) and their prescribing physicians will be blind to medication treatment.