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 degrees 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.