CDC, White House Warn of ‘Rhino Tranq’ Medetomidine Spreading in Fentanyl Supply

The CDC and the White House Office of National Drug Control Policy have issued a national health advisory warning that the veterinary sedative medetomidine—dubbed “rhino tranq,” “mede,” or “dex”—is increasingly showing up mixed with fentanyl in the U.S. illicit drug supply. Federal surveillance data show medetomidine detections in drug samples jumped from 247 cases in 2023 to 2,616 in 2024 and 8,233 in 2025, with about 98% of positive samples also containing fentanyl and confirmed spread across at least 18 states and Washington, D.C., especially in the Northeast and Midwest. The alpha‑2 agonist causes deep, prolonged sedation, slow heart rate, low blood pressure and respiratory depression, and naloxone (Narcan) does not reverse its effects, leaving overdose patients at risk even after standard opioid reversal. Clinicians are being warned to expect severe, rapidly evolving withdrawal that can peak 18–36 hours after use and may require ICU‑level care, as seen in a May 2024 Chicago overdose cluster tied to medetomidine‑laced opioids that involved potentially more than 175 incidents, at least 16 hospitalizations and one death. The advisory underscores how the U.S. overdose crisis is being driven not just by fentanyl itself but by increasingly toxic, hard‑to‑detect sedative combinations that standard tox screens can miss, raising the stakes for emergency rooms, harm‑reduction programs and first responders.