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Opioids are substances that act on the nervous system in a similar way to opiates such as morphine and codeine.〔 In a medical context the term usually indicates medications that are artificially made rather than extracted from opium. Common examples include oxycodone, hydrocodone and hydromorphone. Opioids are primarily used in medicine for the treatment of pain. The side effects of opioids include sedation, respiratory depression, constipation, and a strong sense of euphoria. Opioid dependence can develop with ongoing administration, leading to a withdrawal syndrome with abrupt discontinuation. Morphine-like opioids are well known for their addictive properties, and for their ability to produce euphoria, motivating some to use opioids recreationally. They can cause death in overdose from respiratory depression. A number of substances occurring naturally in the body that can decrease the sensation of pain are also classified as opioids. Opioid like compounds found in natural opium latex are classified as opiates, not opioids. In 2013 between 28 and 38 million people used opioids recreationally (0.6% to 0.8% of the global population between the ages of 15 and 65). Opioids work by binding to opioid receptors, which are found principally in the central and peripheral nervous system and the gastrointestinal tract. These receptors mediate both the psychoactive and the somatic effects of opioids. Opioids are among the world's oldest known drugs; the medical use of the opium poppy predates recorded history. Although the term ''opiate'' is often used as a synonym for ''opioid'', the term ''opiate'' is properly limited to the natural alkaloids found in the resin of the ''Papaver somniferum'' (opium poppy), while ''opioid'' refers to synthetic substances.〔 ==Definition== The term "opioid" was first used in the early 1960s. Its basic meaning is "opiate-like" ("opiates" being a set of narcotic drugs derived from opium), and many sources do not define it more explicitly than that. The first scientific publication to use it, in 1963, included a footnote stating, ''"In this paper, the term, 'opioid', is used in the sense originally proposed by DR. GEORGE H. ACHESON (personal communication) to refer to any chemical compound with morphine-like activities"''.〔 By the late 1960s, it came to be understood that opiate effects are mediated by activation of specific molecular receptors in the nervous system, which were termed "opioid receptors". The definition of "opioid" was later refined to refer to substances that have morphine-like activities that are mediated by the activation of opioid receptors. One modern pharmacology textbook states: ''"the term opioid applies to all agonists and antagonists with morphine-like activity, and also the naturally occurring and synthetic opioid peptides"''. Some sources use the term "opioid" to exclude opiates, but the majority use it inclusively. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「opioid」の詳細全文を読む スポンサード リンク
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