Norfentanyl detection after negative confirmatory testing following heavy illicit fentanyl exposure: A two‐patient case series

Background and Objectives Prolonged fentanyl detection may complicate urine drug testing (UDT). We describe norfentanyl detection after negative confirmatory testing. Methods Two patients ( N = 2) entering residential treatment after heavy illicitly manufactured fentanyl exposure underwent clinically indicated serial UDT with confirmatory LC‐MS/MS. Results Both had negative confirmatory results followed by subsequent low‐level urinary norfentanyl detection. Recurrent exposure could not be excluded. Discussion These findings demonstrate diagnostic uncertainty rather than a defined pharmacokinetic mechanism. Conclusions and Scientific Significance Low‐level norfentanyl after negative confirmatory testing should prompt longitudinal assessment rather than automatic attribution to recurrent use or prolonged detection.