This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, 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: None