Testing for Nonprescribed Fentanyl and Percentage of Positive Test Results Among Patients with Opioid Use Disorder — United States, 2019–2020 Posted on December 16, 2021 By Becky Carter Justin K. Niles, MA; Jeffrey Gudin, MD; Alana M. Vivolo-Kantor, PhD; R. Matthew Gladden, PhD; Desiree Mustaquim, PhD; Puja Seth, PhD; Harvey W. Kaufman, MD MMWR Morb Mortal Wkly Rep 2021;70:1649–1651 Access article Chemistry, Seized Drugs/Controlled Substances, Toxicology