Constipation is a known complication of the postoperative period after spinal surgery, where prescription pain medicines called opioids are traditionally used in high doses for the treatment of surgery-related pain. The goal of this study is to determine the effectiveness of Movantik (naloxegol)-a FDA-approved drug used to treat constipation that is caused by opioids-in preventing constipation in patients undergoing spinal fusion surgery at MGH.