This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pancreas, Subject name: Pharmacology
[{'content': 'Which of the following oral hypoglycemic agent is preferred in obese patients? \nSelect and explain. \nA. Tolbutamide, B. Glipizide, C. Gliclazide, D. Metformin', 'role': 'user'}, {'content': "Answer: D \nExplanation: Metformin doesn't cause weight gain. It may rather cause weight loss. So, it is preferred in obese patients.", 'role': 'assistant'}]