opioid

Definition / meaning of opioid

A substance used to treat moderate to severe pain. Opioids are like opiates, such as morphine and codeine, but are not made from opium. Opioids bind to opioid receptors in the central nervous system. Opioids used to be called narcotics. An opioid is a type of alkaloid.

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Source(s):

The Web site of the National Cancer Institute (http://www.cancer.gov/)

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