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: Pharmacology
Naltrexone is: March 2013 
Select and explain. 
A. (mu) agonist, B. 6 (delta) agonist, C. lc (kappa) antagonist, D. NOP receptor antagonist
C: lc (kappa) antagonist
Answer: C: lc (kappa) antagonist 
Explanation: Ans. C i.e. lc antagonist Naltrexone is an opioid receptor antagonist used primarily in the management of alcohol dependence and opioid dependence.