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
An unknown patient presents with pyrexia, constricted pupils, hypotension, cyanosis and stupor progressing to coma. Poisoning is due to - 
Select and explain. 
A. Phenobarbitone, B. Cannabis, C. Dhatura, D. Diphenhydramine
A: Phenobarbitone
Answer: A: Phenobarbitone 
Explanation: Among the given four options, only Phenobarbitone (Barbiturate) can cause constricted pupils.
All the given symptoms can occur in barbiturates (phenobarbitone) poisoning.