Expanding Oversight of Opioid Prescribing and Payment Act of 2018 (Sec. 2) This bill requires the Medicare Payment Advisory Commission to report to Congress on: (1) how Medicare pays for opioid and non-opioid pain management treatments in inpatient and outpatient hospital settings; (2) current incentives for prescribing opioid and non-opioid treatments under Medicare inpatient and outpatient prospective payment systems, along with recommendations to address any identified adverse incentives; and (3) how opioid use is currently tracked and monitored through Medicare and any areas for improvement.