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Background A combination of opioid and nonopioid analgesic drugs may improve the quality of postoperative analgesia as well as reduce opioid requirements and their associated side effects. Studies have shown synergism between gabapentin and morphine in animal and human experiments and in the treatment of incisional pain. Therefore, the authors investigated, in a randomized, placebo-controlled, double-blind study, the effects of gabapentin on acute postoperative pain and morphine consumption in patients undergoing spinal surgery. Methods After standard premedication, 25 patients in the control group received oral placebo, and 25 patients in the gabapentin group received 1,200 mg of gabapentin, 1 h before surgery in a randomized fashion. Anesthesia was induced with propofol and cisatracurium and was maintained with sevoflurane and remifentanil. The total intraoperative remifentanil consumption by each patient was noted. All patients postoperatively received patient-controlled analgesia with morphine (1 mg/ml) with an incremental dose of 2 mg, a lockout interval of 10 min, and a 4-h limit of 40 mg. The incremental dose was increased to 3 mg, and the 4-h limit to 50 mg, if analgesia was inadequate after 1 h. Patients were questioned for the first 1 h in the PACU and were later evaluated in the ward at 1, 2, 4, 6, 12, and 24 h. Pain scores, heart rate, oxygen saturation measured by pulse oximetry, mean blood pressure, respiratory rate, sedation, morphine use, and total dose of morphine were recorded. Results Overall, pain scores at 1, 2, and 4 h were significantly lower in the gabapentin group when compared with the placebo group. Total morphine consumption in the gabapentin group was 16.3 +/- 8.9 mg (mean +/- SD) versus 42.8 +/- 10.9 mg in the placebo patients. The incidence of vomiting and urinary retention was significantly (P < 0.05) higher in the placebo group, but there was no difference in incidence of other adverse effects between the groups. Conclusions Preoperative oral gabapentin decreased pain scores in the early postoperative period and postoperative morphine consumption in spinal surgery patients while decreasing some morphine-associated side effects.