ENHANCEMENT OF MORPHINE ANALGESIA BY THE ALPHA(2)-ADRENERGIC ANTAGONIST YOHIMBINE

Although interactions between opioids and adrenergic agonists in the t reatment of pain have been demonstrated in humans, the contribution of specific adrenergic receptors in this interaction remains to be clari fied. In a double-blind, placebo-controlled study in male patients wit h postoperative dental pain, we investigated the effect of preoperativ e administration of the alpha(2)-adrenergic antagonist, yohimbine, on analgesia produced by postoperative intravenous morphine. Although yoh imbine by itself did not affect the pain, the overall analgesic effect of morphine was significantly enhanced in the presence of yohimbine. This report is the first to demonstrate that an alpha(2)-adrenergic an tagonist enhances opiate analgesia in humans.