Endorphins are natural opioid peptides produced by the body. They reduce the perception of pain and can produce feelings of well-being or euphoria.

The name combines “endogenous” and “morphine.” Endorphins bind to the same receptors that are activated by opium-derived drugs, which is why morphine and heroin are so effective at blocking pain—and so addictive. The body releases endorphins in response to stress, pain, vigorous exercise, and certain forms of stimulation. The “runner’s high” reported by some endurance athletes is partly attributed to this release.

Endorphins modulate pain at multiple levels of the nervous system, including the spinal cord and brainstem. They also influence mood, appetite, and immune function. Synthetic drugs that block opioid receptors can reverse both the pain-relieving effects of endorphins and the respiratory depression caused by opioid overdose.

When the body needs to keep functioning despite injury or extreme effort, endorphins provide an internal buffer against pain.