Opioids, pain and addiction: Cause and consequence

Abstract

This chapter describes the developments in understanding of the effects of opioids on the pain response. Long-term opioid administration is associated with physiological dependence and tolerance. Opioid-maintained patients administering methadone show marked tolerance, as opioid effects are relatively small compared to what a similar methadone dose would produce in an opioid-naive person. Experimental pain models can be used to measure different aspects of pain perception. Pain can be induced by electrical, thermal, ischemic, chemical, or mechanical methods. These experimental models yield reproducible and reliable data useful for the assessment of pain sensitivity and tolerance. The research investigating the pain sensitivity of chronic pain patients managed with long-term administration of methadone or morphine shows that people in this group exhibit a similar response to experimentally induced pain when evaluated against methadone maintained patients in treatment for opioid addiction. It is found that opioid cross-tolerance and hyperalgesia are significant barriers to the provision of effective analgesia in the opioid-dependent patient. It is suggested that stabilizing patients on a maintenance agent such as methadone or buprenorphine achieves only part of the process of reversing addiction. © 2007 Elsevier B.V. All rights reserved.