Introduction <p>Obesity and overweight have become a global epidemic, impacting people of all ages and socioeconomic status. Metabolic bariatric surgery remains the most effective and long-lasting way to lose weight and address obesity-related conditions. Effective pain management is crucial for a successful recovery after surgery. This randomized double-blind study aimed to compare the analgesic efficacy of ultrasound-guided trans-muscular quadratus lumborum (QL) block to preperitoneal local anesthetic infiltration during laparoscopic bariatric surgery and in the early postoperative period.</p> Methods <p>Eligible patients undergoing laparoscopic bariatric surgery under general anesthesia were randomly allocated to one of two equal groups receiving either bilateral ultrasound guided QL block or laparoscopic preperitoneal bupivacaine infiltration. The primary outcome was patient-reported pain scores at 1, 2, 4, 6, 12, and 24 h postoperatively. Secondary outcome measure were intraoperative fentanyl requirements, postoperative morphine requirements, and incidence of postoperative nausea and vomiting.</p> Results <p>A total of 44 patients were included and randomized equally into two groups. The QL block group had significantly longer block times and surgical durations compared to the preperitoneal local anesthetic infiltration group (p = 0.001 and p = 0.019, respectively). Intraoperative fentanyl requirements were similar between groups; however, postoperative morphine consumption was significantly lower, and the time to first morphine dose was significantly longer in the quadratus lumborum block group (p = 0.001 and p = 0.002, respectively). Postoperative nausea and vomiting occurred significantly less frequently in the QL block group (p = 0.04), and pain scores were significantly lower in this group during the first 6 h postoperatively (p &lt; 0.01).</p> Conclusion <p>The QL block was associated with reduced postoperative opioid consumption, lower early postoperative pain scores, and prolonged analgesic effect compared to preperitoneal infiltration. Optimizing anesthesia techniques in laparoscopic sleeve gastrectomy is essential for minimizing opioid use, reducing the risk of chronic postsurgical pain, and limiting opioid-related adverse effects. Further studies are warranted to evaluate and compare the efficacy of QL block versus preperitoneal infiltration in other types of metabolic bariatric surgery.</p> Key points <p><Table Float="No" ID="Taba"> <tgroup cols="1"> <colspec align="left" colname="c1" colnum="1" /> <tbody> <row> <entry align="left" colname="c1"> <p>1. The quadratus lumborum block provided stronger early postoperative analgesia, reflected by consistently lower pain scores during the first hours after surgery.</p> </entry> </row> <row> <entry align="left" colname="c1"> <p>2. Patients who received the quadratus lumborum block required less post operative morphine and had a longer interval before their first opioid dose.</p> </entry> </row> <row> <entry align="left" colname="c1"> <p>3. The incidence of postoperative nausea and vomiting was lower in the quadratus lumborum block group, supporting its opioid-sparing advantages.</p> </entry> </row> </tbody> </tgroup> </Table></p>