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: Surgery
Which of the following drugs cause relaxation of LES? 1. Nitrates 2. Histamine blockers 3. Morphine 4. Atropine 5. Calcium channel blockers 
Select and explain. 
A. 1,2 & 3, B. 1,4 & 5, C. 1,2 & 5, D. All
B: 1,4 & 5
Answer: B: 1,4 & 5 
Explanation: Factor causing relaxation of LES Factor increasing LES pressure Pharmacological agents:nitrates, anticholinergics, barbiturates, calcium channel blockers, caffeine, theophylline, diazepam, dopamine, prostaglandin E1 and E2 and meperidine Pepperdine Chocolate Coffee Alcohol Smoking Fat Antacids Cholinergics Domperidone Metoclopramide Prostaglandin F2 Also know: LES pressure is higher in the supine position than in the upright position. Ref: Schwarz 9/e, Page 812; Harrison 17/e, Page 1741.