Naloxone is a potent and rapidly acting narcotic antagonist, with a duration of action which is shorter (3 to 4 hours) than that of heroin. In a clinical trial of naloxone in the treatment of heroin dependence, a daily oral dose of 100 mg. at 8 A.M. and 7 P.M. effectively blockaded 20 mg. of heroin, with partial blockade of 40 mg., for up to 10 hours after the morning dose. In narcotic antagonism therapy of opiate dependence, naloxone has the advantages of potency, rapid action, absence of secondary effects, and acceptability. It has the disadvantages of brief action and high cost.