Which adverse effect is most life-threatening and may require naloxone?

• A. Drowsiness
• B. Itching
• C. Constipation
• D. Respiratory depression

Answer: (D)

Opioids can suppress the brain’s breathing drive by activating mu receptors in the brainstem, which dampens the response to carbon dioxide and lowers both respiratory rate and depth. This can rapidly lead to hypoxemia and life-threatening respiratory failure, making respiratory depression the most dangerous adverse effect. Naloxone is a competitive opioid receptor antagonist that quickly displaces opioids from their receptors, restoring normal respiratory drive and reversing the life-threatening depression. That’s why naloxone is used in suspected opioid-induced respiratory depression. The other effects—drowsiness, itching, and constipation—are uncomfortable and common but do not by themselves cause immediate danger or require reversal with naloxone in the same urgent way. Drowsiness is CNS sedation, itching stems from histamine release, and constipation is a slower GI effect; none pose the same acute risk as respiratory failure.