Tehran University of Medical Sciences Archives of Anesthesiology and Critical Care 2423-5849 0 0 2026 06 22 1621 1621 Seyed Hossein Hamidi Department of Anesthesiology, School of Medicine, Babol University of Medical Sciences, Babol, Iran. Nadia Banihashem Department of Anesthesiology, School of Medicine, Babol University of Medical Sciences, Babol, Iran. Parviz Amri Department of Anesthesiology, School of Medicine, Babol University of Medical Sciences, Babol, Iran. Amin Ghanbarpour Juybari Department of Anesthesiology, School of Medicine, Mazandaran University of Medical Sciences, Sari, Iran. Zeinab Babaei Nesami Department of Anesthesiology, School of Medicine, Babol University of Medical Sciences, Babol, Iran. 2026 04 21 2026 05 11 Background: Postoperative pain remains one of the most prevalent clinical challenges and, despite advances in anesthesia and analgesia, is not yet fully measurable or optimally controlled. Although morphine is among the most commonly used opioids for postoperative pain management, its adverse effect profile imposes limitations on its clinical utility. Methadone, a long-acting opioid with multiple mechanisms of action, may represent a suitable alternative for improving postoperative analgesic quality. However, evidence comparing intramuscular methadone with intramuscular morphine in spinal surgeries is limited. This study aimed to compare the effects of intramuscular methadone and morphine on pain intensity, opioid requirements, recovery time, and postoperative adverse effects following lumbar disc surgery. Methods: This double-blind randomized clinical trial was conducted on 80 patients scheduled for lumbar disc surgery with American Society of Anesthesiologists (ASA) physical status I–II. Patients were randomly assigned into two equal groups to receive either intramuscular methadone (0.1 mg/kg) or intramuscular morphine (0.1 mg/kg), administered 30 minutes prior to the end of surgery. Pain intensity was assessed using the Visual Analog Scale (VAS) at 4, 8, 12, and 24 hours after extubation. Additionally, rescue morphine consumption, time to achieve an Aldrete score >9, hemodynamic parameters, and the incidence of adverse effects were compared between the groups. Data were analyzed using SPSS software with appropriate statistical tests. Results: Mean pain scores at all measured time points were significantly lower in the methadone group compared to the morphine group (p < 0.001). Rescue morphine consumption within the first 24 hours postoperatively was also significantly lower in the methadone group (p < 0.001). Patients receiving methadone achieved an Aldrete score >9 in a shorter time and demonstrated greater hemodynamic stability. The incidence of hypotension and bradycardia was higher in the morphine group, whereas no significant difference was observed between the groups regarding nausea and vomiting. Conclusion: The findings indicate that intramuscular methadone provides more effective postoperative pain control than intramuscular morphine following lumbar disc surgery. It is associated with reduced need for rescue opioids, improved recovery indices, and a lower incidence of certain adverse effects. Methadone may therefore be considered a safe and effective option in postoperative pain management protocols for spinal surgeries. https://aacc.tums.ac.ir/index.php/aacc/article/view/1621