Dextromethorphan differs from codeine in:: (A) Its antitussive action can be blocked by naloxone, (B) Depresses mucocilliary function of the airway mucosa, (C) Addiction common, (D) Causes no constipation
Answer is D. Dextromethorphan is a synthetic opiod derivative with antitussuive actions like codeine but with lesser side effects. It does not cause constipation and has no addiction liability but can cause nausea and drowsiness. Ref KD Tripathi 8th ed.