Ninety-two patients scheduled with an elective multilevel lumbar laminectomy (L3−S1) with fusion were randomized into either receiving 0.2 mg of preoperative intrathecal morphine (ITM) or a control of saline solution. The primary outcome measured was post-operative pain at rest and during movement through a Visual Analogue Scale (VAS) at at 1, 3, 6, 12, 24, 48, and 72 hours after operation. Secondary outcomes measured included the following: vitals (heart rate and mean arterial pressure) both intra-operation and post-operation, time to movement, length of hospital stay, incidence of adverse events, patient-reported comfort and satisfaction, time to first analgesic use, incidence of additional analgesic use, sedation scores using the Ramsay scale, as well as propofol, remifentanil, and sufentanil consumption. Results revealed significantly VAS pain scores up to 24 hours post-operation in ITM group compared to the control, as well as significantly lower consumption of analgesics.