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: Psychiatry
[{'content': 'Which drug is most commonly used world wide in maintenance treatment for opioid dependence: \nSelect and explain. \nA. Naltrexone, B. Methadone, C. Imipramine, D. Disulfiram', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Methadone', 'role': 'assistant'}]