40 patients scheduled for primary unilateral TKA were randomized to undergo the procedure with spinal anaesthesia with or without a loading dose of intravenous dexmedetomidine. The purpose of this study was to determine if dexmedetomidine was associated with significantly decreased postoperative consumption of morphine when compared to placebo up to 24 hours postoperatively. Secondary outcomes of interest included time to first analgesic request (PCA), pain experienced at rest, time to discharge from PACU, patient satisfaction with analgesia, hemodynamic and respiratory changes, and opioid-related adverse effects. Results demonstrated that patients in the dexmedetomidine group had significantly lower mean cumulative morphine consumption at 6, 12, and 24 hours. Additionally, patients treated with dexmedetomidine were observed with significantly delayed time until first analgesic request, a lower number of cases of itchiness and nausea/vomiting, lower intraoperative mean arterial pressure, longer time to PACU discharge, and greater patient satisfaction.