This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Adrenergic System, Subject name: Pharmacology
Which of the following is NOT an alpha adrenoceptor agonist? 
Select and explain. 
A. Clonidine, B. Methyldopa, C. Guanabenz, D. Guanfacine
B: Methyldopa
Answer: B: Methyldopa 
Explanation: Ans. (B) Methyldopa(Ref: KDT 8th/e p612)Methyl dopa itself is not an a2 agonist but it is converted to an active metabolite a-methyl norepinephrine which possesses a2 agonistic action. All other drugs listed in the question are a2 agonists for the treatment of hypertension.