Quadazocine (WIN-44,441) is an opioid antagonist of the benzomorphan family which is used in scientific research. It acts as a silent antagonist at all three of the major opioid receptorsâÂÂü, ú, and ô, but with a significant preference in affinity for the ü receptor and the ú<sub>2</sub> subtype. As such, it has been touted as a "ú<sub>2</sub>-selective" antagonist, though this is not entirely accurate on account of its similar affinity for the ü receptor. As would be expected, quadazocine reverses the effects (e.g., analgesia) of opioid agonists like morphine and fentanyl in animals.