Which adverse effect risk increases with higher morphine doses?

• A. Hypotension
• B. Nausea
• C. Urinary retention
• D. Respiratory depression

Answer: (D)

The main idea here is that opioid effects rise with higher doses, and the most dangerous, dose-limiting risk from morphine is respiratory depression. Morphine activates μ-opioid receptors in the brainstem, which blunts the ventilatory response to carbon dioxide. As the dose increases, tidal volume and respiratory rate fall, potentially leading to hypoventilation, hypoxemia, and apnea. This effect is directly tied to how much opioid is in the system, making it the key dose-related adverse outcome to monitor and mitigate.

Other adverse effects like nausea, urinary retention, and hypotension can also become more likely as dose climbs, but they are generally less life-threatening and not as consistently limiting to dose increases as respiratory depression.