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Background: The administration of an analgesic drug prior to nociceptive surgical stimulus could result in a better postoperative pain management. The aim of this study was to evaluate the effect of preoperative oral morphine sulphate on postoperative pain relief., Methods: Sixty patients undergoing major abdominal surgery were randomly assigned to premedication with 0.5 mg/kg oral morphine sulphate (oral morphine group) or 0.05 mg/kg oral midazolam (active placebo group). Primary outcome was efficacy of morphine premedication on opioid administration of IntraVenous Patient Controlled Analgesia (IVPCA) doses, at 4, 24, and 48 hours after completion of surgery and reducing static and dynamic visual analogue scale (sVAS and dVAS) scores. Secondary outcome was the time needed for the recovery of canalization of the gastro-intestinal tract. It was also evaluated fentanyl intraoperative consumption. Statistical analysis was performed by linear regression and student t test. Values of P<0.05 were considered significant., Results: The two groups were comparable with respect to patient characteristics. At 24 and 48 hours post surgery, administered IVPCA doses were reduced in the oral morphine group compared to the active placebo group (P<0.05). Values of sVAS and dVAS were significantly lower in the oral morphine group compared to the active placebo group at all assessment times (P<0.05). Fentanyl consumption was similar in both groups. Needs of a ketorolac rescue dose was greater in the ap versus the om group (21 patients in the ap vs 9 patients in the om group, P<0.001). Mean gastrointestinal canalization did not significantly differ between groups., Conclusions: In major abdominal surgery, premedication with oral morphine sulphate produces better postoperative pain control and has an opioid-sparing effect without delaying gastrointestinal canalization time.