EFFECTS OF ORAL MORPHINE ON COLD PRESSOR TOLERANCE TIME AND NEUROPSYCHOLOGICAL PERFORMANCE

We investigated the analgesic effects of escalating doses (0.214, 0.28 6, 0.357, and 0.429 mg/kg) of oral morphine on tolerance to painful co ld pressor in a double-blind, active placebo-controlled (diphenhydrami ne) study in 45 normal volunteers. The highest dose of morphine admini stered is equivalent to the starting dose recommended by the Agency of Health Care Policy and Research for the management of cancer pain and acute postoperative pain. We assessed analgesia in terms of cold pres sor tolerance time and self-reported ratings of pain intensity and unp leasantness. Subjects receiving the highest dose of oral morphine show ed significantly higher tolerance time than subjects receiving diphenh ydramine. Neither morphine or diphenhydramine significantly reduced ra tings of pain intensity and unpleasantness. neuropsychological testing revealed that the two highest doses of morphine impaired the episodic retrieval of a word list, but the same doses did not affect motor, pe rceptual, or attentional tasks.