Abstract

Using a variety of subjective and objective measures, the relative potency of heroin to morphine administered intravenously to postaddicts found 1.80 to 2.66 mg of morphine sulfate equal to 1 mg of heroin. In addition, it was found that postaddicts could identify heroin and morphine as such with a high degree of accuracy when these agents were administered intravenously either on an acute or chronic basis. Though postaddicts showed no preference for one or the other of these drugs when administered on a single injection basis, five out of eight expressed a preference for heroin in the short-term addiction study. However, on the basis of postaddicts' reports on "the most important effects of morphine and heroin," no constellation of effects could be discerned that explained the preference for heroin. Equipotent doses of these drugs had quite comparable action time courses when administered intravenously, and on this basis there was no marked difference in their ability to produce feelings of "euphoria," ambition, nervousness, relaxation, drowsiness, or sleepiness. Although the heroin abstinence syndrome was of shorter duration than that of morphine, the peak intensity was quite comparable for the two drugs. Data acquired during short-term addiction studies did not support the statement that tolerance develops more rapidly to heroin than to morphine. These findings have been discussed in relation to the physicochemical properties of heroin and morphine and the metabolism of heroin.