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: Psychiatry
Which of the following is not used to treat ADHD? 
Select and explain. 
A. Dexamphetamine, B. Dexmethylphenidate, C. Dextromethorphan, D. Clonidine
C: Dextromethorphan
Answer: C: Dextromethorphan 
Explanation: Dextromethorphan is a NMDA antagonist used as cough suppressant.