endorphin

endorphin [en-dor´fin]
one of a group of opiate-like peptides produced naturally by the body at neural synapses at various points in the central nervous system pathways, where they modulate the transmission of pain perceptions. The term endorphin was coined by combining the words endogenous and morphine. Like morphine, endorphins raise the pain threshold and produce sedation and euphoria; the effects are blocked by naloxone, a narcotic antagonist