This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Pharmacology
[{'content': 'Constipation is caused by all of the following drugs except \nSelect and explain. \nA. Neostigmine, B. Atropine, C. Morphine, D. Fentanyl', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (A) Neostigmine(Ref: KDT 6th/e p101, 455)Neostigmine is an inhibitor of acetylcholinesterase and thus acts like a cholinergic drug. Therefore, it can produce diarrhea (not constipation).Atropine is an anti-cholinergic drug, thus can cause constipation.Morphine and fentanyl are opioids. These can also result in constipation.', 'role': 'assistant'}]