Naltrexone: Physiological and psychological effects of single doses

An ascending series of single doses of the narcotic antagonist naltrexone, ranging from 20 to 160 mg, was administered to 8 abstinent former addicts in order to assess agonistic activity and any toxic side effects. There was little alteration of normal body function. Significant, but small, changes in sublingual temperature (0.4° F decrease), and diastolic blood pressure (1.7 mm Hg increase) were induced. Among the battery of tests assessing behavioral or mood feeling variables, only 2 showed significant between-condition effects: facilitated performance on the Cross-out Test (attention and perception), and a dose-related decrease in Morphine-Benzedrine Group (MBG) scores of the Addiction Research Center Inventory (ARCI) (mild euphoria). On the whole, subjects had few subjective reactions or unpleasant side effects. Naltrexone appears to be a safe, nontoxic medication in the dosage range examined.