Efficacy of Suvorexant in Patients With Effectively Treated Restless Legs Syndrome and Persistent Chronic Insomnia

Inclusion Criteria: 1. Men or women of any ethnic origin 2. Written informed consent is obtained 3. Speaks and writes in English 4. A willingness and ability to comply with study procedures 5. Age 25-85 years 6. Diagnosis of RLS via Cambridge-Hopkins RLS questionnaire 7. International Restless Legs Syndrome Study Group scale score (IRLS) \< 15 8. RLS treatment with a dopaminergic agonist or an alpha-2-delta agent 9. No changes in RLS medication in the previous month 10. DSM-5 criteria for Insomnia Disorder 11. Report a total sleep time ≤ 7 hours and wake after sleep onset (WASO) \> 45 minutes on 7 or more of the 14 nightly sleep logs during both the initial 2-week screening period and the two-week screening run-in period. WASO does not decrease by more than 50% on the 2-week sleep diary obtained between the screening visit and the randomization visit Exclusion Criteria: 1. Diagnosis of moderate/severe obstructive sleep apnea (AHI \> 30) not using continuous positive airway pressure therapy (CPAP) (can be included if CPAP adherent), or other untreated primary sleep disorders (e.g. narcolepsy) 2. Shift workers 3. Unwillingness to not use sedative-hypnotics (other than suvorexant) during the study period 4. Unwillingness to maintain stable RLS medication during the study unless medically indicated 5. Current use of an opiate medication 6. Unwillingness to not take stimulants (e.g. caffeine) after 4:00 pm during the study 7. Current major depressive episode, by report and as indicated by the Patient Health Questionnaire (PHQ-9) 8. Lifetime history of bipolar disorder, psychosis, or other serious psychiatric illness 9. Current alcohol/substance use disorder 10. BMI ≥ 40 kg/m\^2 11. Renal or hepatic disease judged to interfere with drug metabolism and excretion 12. Pregnancy or breastfeeding 13. Malignancy within past 2 years 14. Surgery within past 3 months 15. Neurological disorder or cardiovascular disease raising safety concerns about use of suvorexant and/or judged to interfere with ability to assess efficacy of the treatment 16. Medical instability considered to interfere with study procedures 17. Concomitant medications with drug interaction or co-administration concerns 18. Contraindications or allergic responses to suvorexant 19. History of being treated with suvorexant 20. Travel across two time-zones during the week prior to enrollment 21. Greater than 6 cups of coffee per day