<p>Effective postoperative pain management is crucial, particularly in lumbar vertebral fusion surgery. Intrathecal morphine (ITM) offers targeted pain relief with reduced systemic side effects. To assess the efficacy and safety of 0.3 mg ITM for postoperative analgesia in opioid-dependent and non-opioid-dependent patients undergoing lumbar vertebral fusion surgery. This randomized controlled trial enrolled opioid-dependent and non-opioid-dependent patient’s lumbar vertebral fusion surgery, divided into four groups (25 per group). Patients received either ITM or nothing. Visual analog scale (VAS) scores were assessed at various time points (baseline, 4, 8, 12, 18, and 24 h) as primary outcome. During this study, side effects and extra requirements of morphine were assessed. Finally, 100 patients were analyzed after 24 h follow-up. No significant difference in baseline VAS scores existed between groups. However, a significant relationship between intervention and control groups was observed at 4, 8, 12, and 18 h in both opioid-dependent and non-opioid-dependent patients. Opioid-dependent patients showed no significant relationship after 24 h. ITM reduced total morphine requirements and morphine-associated side effects were minimal. ITM (0.3 mg) is an effective and safe alternative for postoperative analgesia in lumbar vertebral fusion surgery for both opioid-dependent and non-opioid-dependent patients. Future studies should investigate optimal dosages and combinations with other pain medications.</p>