Experimental: Cognitive Behavioral Treatment for Insomnia (CBT-I)

Participants in this treatment group will receive CBT-I. CBT-I sessions will occur weekly for the first 4 sessions and biweekly for the last 2 sessions (treatment phase is thus 8 weeks). : Graduate level students in clinical psychology will serve as therapists for this project.

Experimental: Lemborexant medication

Participants assigned to this group will be prescribed 5 to 10 mg of lemborexant to be taken at bedtime in 5 mg capsules. Lemborexant (Dayvigo) is a Dual Orexin Receptor Antagonist approved by Health Canada for the treatment of adult with insomnia, characterized by difficulties with sleep onset and/or sleep maintenance. Pharmacy staff will package medications for each participant in a generic bottle labeled with the participant's ID code and treatment dates (identical for the lemborexant and placebo arms). Six consultation visits will be conducted during the 8-week treatment phase to monitor treatment response and drug side effects. The starting dose will be 5 mg with titration to 10 mg if needed (i.e., based on clinical response and tolerability) following the first week.

Placebo_comparator: Placebo

Participants assigned to this group will be prescribed 5 to 10 mg of placebo to be taken at bedtime in 5 mg capsules identical to lemborexant. Pharmacy staff will package medications for each participant in a generic bottle labeled with the participant's ID code and treatment dates (identical for the lemborexant and placebo arms). Six consultation visits will be conducted during the 8-week treatment phase to monitor treatment response and drug side effects. The starting dose will be 5 mg with titration to 10 mg if needed (i.e., based on clinical response and tolerability) following the first week.