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
NMDA blocker used as antitussive is 
Select and explain. 
A. Pholcodeine, B. Dextromethorphan, C. Diphenhydramine, D. Aprepitant
B: Dextromethorphan
Answer: B: Dextromethorphan 
Explanation: Dextromethorphan is a NMDA blocker which is a less potent antitussive. Side effects include addiction liability & hallucination.