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Any of various compounds that bind to specific receptors in the central nervous system and have analgesic and narcotic effects, including naturally occurring substances such as morphine; synthetic and semisynthetic drugs such as methadone and oxycodone; and certain peptides produced by the body, such as endorphins. Also called opiate.

o′pi·oid′ adj.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


a. any of a group of substances that resemble morphine in their physiological or pharmacological effects, esp in their pain-relieving properties
b. (modifier) of or relating to such substances: opioid receptor; opioid analgesic.
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014


(ˈoʊ piˌɔɪd)

1. any opiumlike substance, as the endorphins produced by the body or the synthetic compound methadone.
2. pertaining to such a substance.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.


adj & n opioide m
English-Spanish/Spanish-English Medical Dictionary Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.
References in periodicals archive ?
Activation of endogenous opioid gene expression in human keratinocytes and fibroblasts by pulsed radiofrequency energy fields.
According to researchers, findings indicated that emotional responses to external stimuli are mediated by the endogenous opioid system.
"This suggests that the brain's own endogenous opioid system may play a role in wanting to eat beyond what is needed," notes Prof.
(8) Berberine has an antinociceptive effect, which may be in part due to its impact on contractility, or mediated via its interactions with the endogenous opioid system, (9) or via nitric oxide synthesis.
However, recent studies have unveiled that the endogenous opioid system is probably one of the chief modulatory mechanisms related to this process [26-30].
Stress-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis is seen in both diseases with the resultant release of corti-cotropin releasing factor (CRF) and dynorphin, an endogenous opioid peptide (Figure 1(a)).
ENK are produced from a propeptide precursor, proenkephalin (proENK), which is translated from preproenkephalin mRNA that is encoded by a gene distinct from the other endogenous opioid peptides [19, 20].
Recently, it was demonstrated that neurons expressing the dopaminergic receptors were immunopositive for the endogenous opioid met-enkephalin [3].
Researchers have explored the involvement of the endogenous opioid system in the antinociceptive effect of medicinal herbs (Calixto et al.
Central endogenous opioid inhibition of supraoptic oxytocin neurons in pregnant rats.
The endogenous opioid system is involved in a variety of physiological processes such as analgesia, stress, reward or adaptive homeostatic functions (temperature control, water and food intake).
In particular, nicotine enhances the endorphinic mu receptor mRNA and protein expression in brain regions important for drug reward in rodents [4,5] and stimulates endogenous opioid release [6], resulting in mu receptor activation.