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Pain is a complex construct that is defined by the International Association for the Study of Pain (IASP) as “an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.” The current IASP definition of pain was recommended by the Subcommittee on Taxonomy and adopted by the IASP Council in 1979. This definition has become widely accepted by health care professionals and researchers in the pain field and adopted by several professional, governmental, and nongovernmental organizations, including the World Health Organization. In recent years, some in the field have reasoned that advances in our understanding of pain warrant a reevaluation of the definition and have proposed modifications. Therefore, in 2018, the IASP formed a 14-member, multinational Presidential Task Force comprising individuals with broad expertise in clinical and basic science related to pain to evaluate the current definition and accompanying note, and recommend whether they should be retained or changed. This review provides a synopsis of the critical concepts, the analysis of comments from the IASP membership and public, and the committee’s final recommendations for revisions to the definition and notes, which were discussed over a 2-year period. The task force ultimately recommended that the definition of pain be revised to “an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage,” and that the accompanying notes be updated to a bulleted list that included the etymology. The revised definition and notes were unanimously accepted by the IASP Council early this year.1,2 Just as the definition of pain is multifaceted, so too are there multiple options for the treatment of pain. There are multiple drug classes used to treat pain including the opioid analgesics and non-opioid analgesics. Non-opioid analgesics are further divided into drug classes including salicylates (aspirin), non-steroidal anti-inflammatories (such as ibuprofen) and acetaminophen (Tylenol). Other classes are used for pain management as well, including anesthetic agents, skeletal muscle relaxants, and adjuvants (such as some antidepressants).

The focus for this chapter will be the opioid analgesics.


Historically, the term narcotic was often applied to opioid compounds because when taken, they tend to have sedative or sleep-inducing side effects, and high doses can produce a state of unresponsiveness and stupor. However, narcotic is a misleading name, because it describes a side effect rather than the principal therapeutic effect. Besides this misleading name, the term has negative connotations as being “illicit” and illegal. Some opioids are illegal, but many are legally prescribed with FDA approval for medical use. The most common illegal opioid drug is heroin, which has no legal purpose in the U.S.

Current terminology refers to this class as opiate analgesics because some of these compounds are derived from opium. The term opioid represents all types of narcotic analgesic-like agents, regardless of their origin.2 Consequently, most sources preferentially use ...

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