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
[{'content': 'Which of the following inhibits rate limiting step of Norepinephrine synthesis \nSelect and explain. \nA. Cocaine, B. Amphetamine, C. Metyrosine, D. Bretylium', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Metyrosine inhibits tyrosine hydroxylase enzyme, which mediates the rate limiting step of norepinephrine synthesis (i.e conversion of Tyrosine to Dopa).', 'role': 'assistant'}]