To direct the Comptroller General to conduct a study and submit a report to Congress on best practices in use by Federal departments and agencies to reduce opioid usage following medical procedures.

Combating Opioid Misuse By Advancing Treatment Act of 2018 or the COMBAT Act of 2018 This bill requires the Government Accountability Office to conduct a study on best practices used by federal departments and agencies to reduce opioid use following a medical procedure that is conducted, funded, or otherwise supported by such agencies and departments.