Although not always required, an MRO is an important part of an effective drug testing program. An MRO is generally a licensed medical doctor who has special training in substance abuse. Using an MRO helps to protect both the employer and the employees. For example, if a drug test is positive, the MRO reviews the results, makes sure the chain of custody procedures were followed, and contacts the employee to make sure there are no medical or other legitimate reasons for the positive results. For example, some prescription medicines can cause a positive test result. If this is the case, and if a doctor prescribed the medicine, the test is reported as negative. Otherwise, the MRO reports the positive test results to the employer. Only after the MRO his reached his or her final conclusion does the MRO report the result to the employer.