it acts primarily on the mu (some kappa and delta) opioid receptors as an agonist. It will induce similar effects of analgesia as other opioids, however, due to its potency, it will also induce strong side effects such as sedation. Consequently, that is why it is used as a tranquilizer for large animals. Carfentanil interacts predominately with the opioid mu-receptor. These mu-binding sites are discretely distributed in the brain, spinal cord, and other tissues. It exerts its principal pharmacologic effects on the central nervous system. Its primary actions of therapeutic value are analgesia and sedation. Carfentanil also depresses the respiratory centers, depresses the cough reflex, and constricts the pupils.