Sixty-two patients with rotator cuff tears scheduled for an arthroscopic rotator cuff repair were randomized to receive an interscalene brachial plexus block with ropivacaine and dexmedetomidine (DEX) or ropivacaine alone to decrease post-operative pain. The outcomes of interest included pain on a Visual Analog Scale (VAS), patient satisfaction, pain-related cytokine levels (i.e., cortisol, interleukin (IL) 6, IL-8, IL-1b, substance P), time to rebound pain, severity of rebound pain on a VAS, as well as functional scores (i.e., Constant score, American Shoulder and Elbow Surgeons (ASES) score). Outcomes were assessed up to 48 hours post-operation. The results revealed significantly favourable VAS pain scores and patient satisfaction scores up to 18 hours post-operation in the DEX group compared to the control group. IL-6 and IL-8 levels were significantly lower in the DEX group. Cortisol at 6 hours post-operation and Substance P levels at 1 hour post-operation were significantly lower in the DEX group. Whilst the severity of rebound pain was not significantly different between the 2 treatment arms, the time to rebound pain was significantly longer in the DEX group compared to the control group. Thus, the addition of dexmedetomidine appears to prolong the analgesic effects of interscalene brachial plexus nerve blockades in patients undergoing arthroscopic rotator cuff repairs.