Qualitative urine drug assays are frequently used in conjunction with opioid contracts as a means of monitoring use of prescribed controlled substances as well as concurrent use of illicit substances in patients receiving opioids for chronic nonmalignant pain (CNMP) management. Appropriate use of these screening tests, in conjunction with opioid contracts, may provide the health care provider with additional information needed to safely prescribe opioids for selected individuals with CNMP. It is important for the practitioner caring for patients subject to random urine drug screening to understand interferences with the commonly used urine drug assays, as well as knowing options to confirm contested test results. We reviewed the literature on urine drug assay test interferences and present a summary of this information in this article.