Naltrexone is used to maintain abstinence following opioid withdrawal in addicts. It blocks all of the following features of opioid use, except:
Euphoriant effects of opioid
Craving for opioid
Miosis
Respiratory depression
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 opioid like sedation, analgesia, constipation, respiratory depression and Miosis etc but it do not reduce craving.
Central Nervous system