Early Efficacy and Mechanisms of Lemborexant vs. Online CBT-I for Chronic Insomnia with Subthreshold Depression: a Randomized Controlled Trial

INTERVENTION: eCBT‐I group:online cognitive behavioral therapy for insomnia;Lemborexant group:oral lemborexant; CONDITION: This study focuses on a specific clinical population: patients with chronic insomnia disorder (difficulty initiating or maintaining sleep, or early‐morning awakening for >=3 months, accompanied by daytime functional impairments) comorbid with subthreshold depression (presence of depressive symptoms such as low mood or loss of interest for >=2 weeks, PHQ‐9 score 5‐14, not meeting major depression c PRIMARY OUTCOME: Insomnia Severity Index (ISI); SECONDARY OUTCOME: Cognitive Emotion Regulation Questionnaire (CERQ);Dysfunctional Beliefs and Attitudes about Sleep Scale‐16 (DBAS‐16);Polysomnography (PSG);daily sleep diary;Ruminative Responses Scale‐Chinese Version (RRS‐CV);Resting‐state functional magnetic resonance imaging (rs‐fMRI);Generalized Anxiety Disorder 7‐item scale (GAD‐7);Epworth Sleepiness Scale (ESS);Hospital Anxiety and Depression Scale (HADS);Pre‐sleep Arousal Scale (PSAS);Patient Health Questionnaire‐15(PHQ‐15);Munich ChronoType Questionnaire (MCTQ);Patient Health Questionnaire‐9 (PHQ‐9);Columbia‐Suicide Severity Rating Scale (C‐SSRS);Ford Insomnia Response to Stress Test (FIRST);Liver Function Tests (LFTs);Renal Function Tests;Adverse Event Record Form;Complete Blood Count (CBC);Structured Clinical Interview for Sleep and Psychiatric Disorders; INCLUSION CRITERIA: 1. Age between 18 and 65 years (inclusive). 2. Meet the diagnostic criteria for Chronic Insomnia Disorder according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM‐5), with a disease duration of >=3 months. 3. Meet the criteria for "subthreshold depression": presence of >=2 DSM‐5 depressive symptoms (at least one of which is "depressed mood" or "loss of interest/pleasure"), lasting for >=2 weeks, causing clinically significant distress or functional impairment, but not meeting the diagnostic criteria for a major depressive episode; or a total score of 5–14 on the Patient Health Questionnaire‐9 (PHQ‐9), with a score <=1 on item 9 (suicidal ideation). 4. Have a minimum education level equivalent to the completion of grade six, and be proficient in using a smartphone or computer. 5. Voluntarily participate in the study, fully understand, and sign a written informed consent form.