This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Pharmacology
Which of the following drugs causes constipation? 
Select and explain. 
A. Propanolol, B. Verapamil, C. Nitroglycerin, D. Captopril
B: Verapamil
Answer: B: Verapamil 
Explanation: It is a Calcium channel blocker. DOC for chronic PSVT Organic (secondary) constipation due to drugs causes e.g.-opiates, sedatives, anticholinergics including antiparkinsonian, antidepressants and antihistaminics, oral iron, clonidine, verapamil. (REF. ESSENTIALS OF MEDICAL PHARMACOLOGY K.D TRIPATHI-6th edition.Page No-530)