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: Gynaecology & Obstetrics
[{'content': 'Combined oral contraceptives interfere with action of following drugs except \nSelect and explain. \nA. Imipramine, B. Meperidine, C. Metoprotol, D. Metformin', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Combined OCPs do not influence effectiveness of metformin.', 'role': 'assistant'}]