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
Pure opiate antagonists are all of the following 
Select and explain. 
A. Naloxone, B. Nalorphine, C. Nalmefene, D. Naltrexone
B: Nalorphine
Answer: B: Nalorphine 
Explanation: , Nalorphine was the first opiod antagonist introduced in 1951 which could reverse morphine action. Later it was found to have agonistic action or kappa re eptor as well, producing lower ceiling analgesia. It is not used clinically because of dysphoric and psychotomimetic effects. Ref KD Tripathi 8th ed.