Clinical Research Directory

Inclusion Criteria: 1. Chinese aged ≥ 60. 2. Provision of written informed consent. 3. Having a DSM-5 diagnosis of insomnia disorder (i.e., having difficulty initiating sleep, maintaining sleep, or early morning awakening at least three times a week for at least three months, with clinically significant impairment or distress). 4. Having a score of \> 14 on the ISI, indicating clinical insomnia. Exclusion Criteria: 1. Having a current diagnosis or a history of manic or hypomanic episodes, schizophrenia spectrum disorders, neurodevelopmental disorders, neurocognitive disorders, organic mental disorders, intellectual disabilities, or substance abuse or dependence. 2. Having a progressive medical condition directly related to the onset and course of insomnia (e.g., cancer, chronic pain). 3. Undergoing treatment for diseases known to affect sleep (e.g., chemotherapy). 4. Having an untreated sleep disorder that may disrupt sleep continuity and quality (e.g., sleep-disordered breathing) except for insomnia disorder and circadian sleep-wake phase disorder. 5. Having mild to significant cognitive impairment, defined by having a score of \< 22 on MOCA. 6. Concurrent and regular use of extraneous melatonin or melatonin agonist (e.g., ramelteon). 7. Receiving concurrent psychological treatment for insomnia. 8. Meeting potential contraindications for melatonin (e.g., undergoing dialysis) or concurrently using medications that have a potential drug interaction with melatonin (e.g., anticoagulant and anti-platelet). 9. Being a night shift worker.