If naloxone could reverse pain relief when no drugs were present, researchers guessed that the body must have its own pain-relief systems.
“Endorphin,” the word, comes from “endogenous morphine.” A number of such natural chemicals were later found, along with receptors in the brain upon which they and the opioids acted.
via How Staten Island Is Fighting a Raging Heroin and Prescription-Pill Epidemic.
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