<prompt> Which of the following drugs causes constipation?PropanololVerapamilNitroglycerinCaptopril  <response>: 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 