This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Central Nervous system, Subject name: Pharmacology
Naltrexone is used for which of the following poisoning? 
Select and explain. 
A. Heroin, B. Atropine, C. Cannabis, D. Diazepam
A: Heroin
Answer: A: Heroin 
Explanation: Ref: KDT 6/e p467 Naltrexone is an orally effective opioid antagonist. It is useful for the maintenance of the patient of opioid poisoning once it has been treated with naloxone. Heroin is an opioid, whose poisoning can be treated by naloxone and naltrexone.