Substance Index
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Opioids are a class of psychoactive substances that relieve pain and produce euphoria, relaxation, and contentment. They also cause sedation. At high doses, opioids slow breathing to a dangerous degree. Opioids imitate endorphins, the natural painkilling chemicals of the body, and act on the same opioid receptors. The name comes from opium, the extract of the poppy, and -oid ("resembling"). The term "opiate" covers only natural poppy derivatives, but "opioid" covers any substance that acts on these receptors.