This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Opioids, Subject name: Pharmacology
Naltrexone is used to maintain abstinence following opioid withdrawal in addicts. It blocks all of the following features of opioid use, except. 
Select and explain. 
A. Euphoriant effects of opioids, B. Craving for opioids, C. Miosis, D. Respiratory depression
B: Craving for opioids
Answer: B: Craving for opioids 
Explanation: Ans. (B) Craving for opioids(Ref: Goodman and Gilman 12th/661)Naltrexone has no action in the absence of agonists but promptly reverses the opioid effects when administered i.v.It can reverse all effects of opioids like sedation, analgesia, constipation, respiratory depression and miosis etc but it do not reduce craving.