Methadone, hydromorphone, and fentanyl are what type of opioid?

• A. Mu agonist
• B. Mu antagonist
• C. Kappa agonist
• D. Delta agonist

Answer: (A)

Opioids work by binding to and activating opioid receptors in the nervous system, with the mu receptor being the primary mediator of analgesia and many characteristic opioid effects. Methadone, hydromorphone, and fentanyl are high-potency synthetic opioids that act as mu receptor agonists, meaning they stimulate these receptors to produce pain relief, euphoria, and, importantly, respiratory depression and constipation. They are not antagonists, and their effects are not primarily driven by kappa or delta receptor activation. So the best description is that these drugs are mu receptor agonists.