The Effect of Opiates on the Pain Threshold in Post-Addicts

One of the characteristics of morphine, when used clinically, is the constancy of its action. In the absence of tolerance, a given dose of morphine can be depended on to give a definite result. With one or two exceptions, this is true regardless of the nature or the anatomical location of the pain, unless this is so severe as to be beyond control by the drug. There is some individual variation in the side effects but the main analgesic action is quite constant. When the pain-threshold-raising action of mor-phine is studied by the Hardy-Wolff technique (1), taking care to avoid the development of tolerance, a fairly constant response is again ob-served (2). The effects are not identical in each individual tested, but are of the same order of magnitude. This report presents results obtained from pain threshold measurements, using morphine and 7 of its derivatives, in a group of men who had been addicted to opiates but who had received no regular doses of these drugs for at least 6 months prior to the study. The post-addiction period ranged from this minimum to a maximum of 8 years. METHODS A Hardy-Wolff apparatus with a 3-second exposure time was used in this study. The lamp was operated from 110 volt A. C. mains through a voltage-regulating trans-former, which reduced line fluctuations to an insignificant amount. The brightness of the lamp was controlled by a Variac and the stimulus intensity was measured with a wattmeter connected in the lamp circuit. Without cali-bration, this does not permit the radiation intensities to be determined in the basic units of calories per cm.2 per second, but since the results of these measurements are usually expressed as a percentage rise above the pre-injection level, the wattmeter readings give sufficient in-formation for determining time-action curves. Since it has been shown that the wattmeter readings are linear