Reemergence of Carfentanil: A Growing Threat in the U.S. Opioid Crisis

All authors conceptualized and drafted the first and subsequent versions of this article. All authors read, revised the drafts and approved the final manuscript. Carfentanyl, a highly potent synthetic opioid originally used as a tranquilizer for large animals, is re-emerging as a significant public health threat in the U.S1–3. The recent sevenfold increase in overdose deaths with carfentanil detected (from 29 in early 2023 to 238 in mid-2024) suggests a rapid resurgence. Unlike the 2016–2017 outbreak, which was localized and had low illegally manufactured fentanyl (IMF) co-detection rates (<25%), the current wave spans 37 states with 87% IMF co-detection, indicating a broader and more integrated presence in the illicit drug supply.4