Carfentanil stabilizes µ opioid receptor conformations that are ultra-efficient in inhibiting cAMP, resistant to naloxone or nalmefene but sensitive to naltrexone. - Endt, Franziska; Guo, Tao; Steinritz, Dirk; Amend, Niko; Gudermann, Thomas; Breit, Andreas (Archives of Toxicology, 2025)