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: Forensic Medicine
[{'content': 'An unknown patient presents with pyrexia, constricted pupils, hypotension, cyanosis and stupor progressing to coma. Poisoning is due to - \nSelect and explain. \nA. Phenobarbitone, B. Cannabis, C. Dhatura, D. Diphenhydramine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Among the given four options, only Phenobarbitone (Barbiturate) can cause constricted pupils.\nAll the given symptoms can occur in barbiturates (phenobarbitone) poisoning.', 'role': 'assistant'}]