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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.
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.
1. any opiumlike substance, as the endorphins produced by the body or the synthetic compound methadone.adj.
2. pertaining to such a substance.