This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Central Nervous system, Subject name: Pharmacology
Dextromethorphan differs from codeine in: 
Select and explain. 
A. Its antitussive action can be blocked by naloxone, B. Depresses mucocilliary function of the airway mucosa, C. Addiction common, D. Causes no constipation
D: Causes no constipation
Answer: D: Causes no constipation 
Explanation: 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.