Naloxone (Narcan) reverses opioid effects because it is which pharmacologic class?

• A. It is an agonist at opioid receptors
• B. It is a receptor antagonist that reverses opioid effects
• C. It is a partial agonist at opioid receptors
• D. It irreversibly binds opioid receptors

Answer: (B)

Naloxone reverses opioid effects because it acts as an opioid receptor antagonist. It binds with high affinity to mu, kappa, and delta receptors but does not activate them. By occupying these receptor sites, it blocks opioids from binding and activating the receptors, thereby reversing the downstream effects such as respiratory depression, sedation, and analgesia. This blocking is competitive and reversible, so naloxone can displace opioids and stop their effects, but as naloxone levels decline, opioids can reoccupy receptors if they’re still present, which is why symptoms can recur. It is not an agonist or a partial agonist, since it does not produce opioid-like effects, and it is not irreversible, since receptor binding is reversible.