Efficacy of Melatonin, Low-dose Quetiapine, or Placebo in Patients With Psychiatric Disorders and Comorbid Insomnia

Inclusion Criteria: * 16 to 64 years of age * ICD-10 diagnosis of a current or previous mental or behavioral disorder (F20-F69, F84, F90-95) * For the diagnoses F84 and F90 a previous period of treatment with melatonin is required * For the 16-17 years old: Non-pharmacological treatment options including sleep hygiene education, weighted blanket or other gravity products have been tested with insufficient effect * Self-reported sleep difficulties at least three times per week in the preceding 3 months * Insomnia Severity Index score ≥11 * Women of childbearing potential: negative pregnancy test at baseline and use of highly effective contraception measures * Informed consent Exclusion Criteria: * Current treatment with melatonin or quetiapine * Severe somatic comorbidity * BMI ≥ 35 kg/m2 * Breastfeeding * Alcohol and/or substance dependency within the last 3 months * Inadequate Danish language skills * Not able to make an informed consent * Increased cardiac risk as assessed by presence of cardiac risk factors, cardiac symptoms, or prolonged QT-interval at baseline ECG