Subjects will receive naloxegol 25mg daily or usual care for a 2-week initial treatment period followed by 3-day washout period, then a 2-week crossover treatment period where subjects will receive naloxegol or usual care. Treatment assignment during the initial and crossover treatment periods will be dictated by the randomization arm. Subjects will also have the option to participate in a 12-week extension phase of naloxegol.