This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Pharmacology
[{'content': 'True about naltrexone is all except \nSelect and explain. \nA. Acts on opioid receptors, B. Is used in treatment of alcohol dependence, C. Is used to reduce craving in dependence, D. Is a opioid agonist', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. d (Is a opioid agonist). (Ref. Pharmacology by KD Tripathi - 6th pg. 467)Agonist-antagonists (K analgesics)Nalorphine, Pentazocine, ButorphanolPartial/weak m-agonist + k antagonistBuprenorphinePure antagonistsNaloxone, Naltrexone, NalmefeneNALTREXONE# Pure opioid antagonist, chemically related to naloxone.# Orally active and long duration of action (1-2 days) makes it suitable for 'opioid blockade' Rx in post-addicts.# It is more potent than naloxone.# Alcohol craving is also reduced by naltrexone; it is being used to prevent relapse of heavy drinking# HepatotoxicNewly developed opioid antagonist Nalmefene:# Hepatotoxic# Has higher oral bioavailability &# Is long acting.", 'role': 'assistant'}]