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 one of the following drugs causes constipation? \nSelect and explain. \nA. Propranolol, B. Verapamil, C. Nitroglycerin, D. Captopril', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Verapamil Drugs causing constipation : Aluminium Hydroxide Ion exchange resins Verapamil Calcium carbonate Barium sulphate Opiates Ferrous sulphate Ganglionic blockers Phenothiazines Tricyclic antidepresants", 'role': 'assistant'}]