An MRO is a licensed physician (MD or DO) with DOT-required training who reviews and verifies drug test results (49 CFR 40.121).

• The MRO reviews the CCF and the laboratory result.
• For a positive, adulterated, substituted, or invalid result, the MRO interviews the employee to see whether there is a legitimate medical explanation, such as a valid prescription.
• The MRO then reports the verified result to the employer's DER and, for CDL drivers, reports verified positives and certain refusals to the Clearinghouse.

The MRO acts as an independent, impartial gatekeeper for the accuracy of the process. Med-Stop provides MRO review services.