Effects of Opioid Drugs on Sleep and Emotion in Patients With Moderate to Severe Cancer Pain

Inclusion Criteria: 1. Aged 18-75 years. 2. Histopathologically or cytologically confirmed diagnosis of malignancy, with moderate to severe cancer-related pain (NRS ≥ 4 points), meeting the WHO three-step analgesic ladder principle, having received opioid analgesic therapy for at least one week with a stable dose and well-controlled pain. 3. ECOG performance status score ≤ 3. 4. Possess basic cognitive function and ability to complete questionnaire-based assessments and wristband-based sleep monitoring. 5. Voluntarily sign the informed consent form and agree to comply with the study follow-up procedures. Exclusion Criteria: 1. Severe cognitive impairment, history of psychiatric disorder, or language/communication barriers that precludes completion of the assessments. 2. History of opioid abuse or dependence; history of alcohol or non-opioid substance abuse. 3. Severe hepatic or renal insufficiency (Child-Pugh Class C or eGFR \< 30 mL/min). 4. Life expectancy \< 3 months. 5. Women of childbearing age without effective contraception, or who are pregnant or breastfeeding. 6. Presence of other serious diseases or special conditions that, in the investigator's judgment, may interfere with the study outcomes. 7. Presence of contraindications to the study drug, such as paralytic ileus, chronic obstructive respiratory disease, or cor pulmonale.