Naltrexone is a long acting, specific mu-opioid receptor antagonist. It can be used to prevent relapse in former opioid dependent patients and former alcohol-dependent patients. Its role in opioid dependence is to block access of self-administered opioids to opioid receptors, and no tolerance to its antagonist activity is likely to develop.^13,18

However, its effect in alcohol dependency is less understood. It is thought that alcohol consumption will reinforce an alcohol-induced stimulation of the endogenous opioid system. Naltrexone reduces the risk of a full relapse if a limited amount of alcohol is consumed, and it will reduce desire for alcohol during abstinence and after ingesting alcohol. It also does not cause a reaction if alcohol is ingested, unlike disulfiram.¹³