Naltrexone is the first safe and effective pharmaceutical adjunct for use in the treatment of alcohol abuse. Theoretically it could be effective also as a means for terminating methadone maintenance and in the treatment of other forms of substance abuse. Two general types of protocols have been used with naltrexone. One protocol is similar to the protocol appropriate for use with disulfiram; it is designed to preclude use of the substance while on naltrexone. The other protocol is based on preclinical research showing that opioid antagonists can cause extinction of alcohol drinking; it is designed to maximize the effects from extinction. The results from the clinical trials are consistent with the conclusion that the major benefits from naltrexone treatment, regardless of protocol, are being caused by extinction. The extinction protocol is better from the position of public health, increasing the range of patients who can be treated, reducing the total cost and allowing patients to be treated with dignity. Pharmacological extinction is a new form of medicine, shown to be highly accessible and effective in treating excessive drinking and providing interesting possibilities for the treatment of other learned behavioural disorders.