Naloxone Metabolism Associated With Unexpected Noroxymorphone Detected in Urine During Pregnancy.

BACKGROUND: Urine drug testing (UDT) is commonly used in obstetrics to monitor opioid use disorder treatment, but interpretation can be difficult and may trigger harmful consequences, including child welfare reporting. Noroxymorphone, also referred to as nornaloxone, may arise from metabolism of naloxone, oxycodone, or oxymorphone and may be detected in patients taking buprenorphine/naloxone. CASES: Two pregnant individuals receiving buprenorphine/naloxone had unexpected presumptive positive opiate screens. Confirmatory testing showed isolated low-level noroxymorphone (46 and 79 ng/mL) without detectable parent opioids, consistent with naloxone metabolism rather than opioid use. Both patients experienced significant distress after the initial results. CONCLUSION: Clinicians should recognize naloxone-associated noroxymorphone to avoid misclassifying return to use. Confirmatory testing and interpretation are essential to prevent harm and preserve clinician-patient trust.