A medical professional, most often a licensed physician, who is responsible for receiving and reviewing all confirmed “positive ” drug-test results from the laboratory. The MRO is generally responsible for contacting all individuals testing “positive ” to inquire about possible prescription or over-the-counter medications which may have caused a “positive ” test result. The MRO must have knowledge of substance-abuse disorders and the appropriate medical training in order to interpret and evaluate “positive ” test results, together with an individual’s history and any other relevant medical information.