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': 'An anti-emetic drug that also decreases acid secretion due to its action on H1 receptors is : \nSelect and explain. \nA. Promethazine, B. Domperidone, C. Metoclopramide, D. Ondansetron', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Promethazine is a first-generation H1-antihistaminic drug. It is indicated for the treatment of allergic reactions. Because of its anticholinergic action and ability to cross the blood-brain barrier, it can be used as an antiemetic (particularly for prophylaxis of motion sickness) and as an anti-Parkinsonian drug (particularly in drug-induced Parkinsonism).\nAcid secretion is reduced mainly by H2-blocking drugs like ranitidine but even H1-antihistaminics can also reduce acid secretion at high doses (due to lack of selectivity at such high dose).', 'role': 'assistant'}]