endorphin

American  

[en-dawr-fin] / ɛnˈdɔr fɪn /

noun

1. any of a group of peptides occurring in the brain and other tissues of vertebrates, and resembling opiates, that react with the brain's opiate receptors to raise the pain threshold.

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endorphin British  

/ ɛnˈdɔːfɪn /

noun

1. any of a class of polypeptides, including enkephalin, occurring naturally in the brain, that bind to pain receptors and so block pain sensation

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endorphin Scientific  

/ ĕn-dôr′fĭn /

1. Any of a group of peptide substances secreted by the anterior portion of the pituitary gland that inhibit the perception of painful stimuli. Endorphins act as neurotransmitters in the pain pathways of the brain and spinal cord. Narcotic drugs may stimulate the secretion of endorphins.

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Closer Look

Endorphins are long chains of amino acids, or polypeptides, that are able to bind to the neuroreceptors in the brain and are capable of relieving pain in a manner similar to that of morphine. There are three major types of endorphins: beta-endorphins are found almost entirely in the pituitary gland, while enkephalins and dynorphins are both distributed throughout the nervous system. Scientists had suspected that analgesic opiates, such as morphine and heroin, worked effectively against pain because the body had receptors that were activated by such drugs. They reasoned that these receptors probably existed because the body itself had natural painkilling compounds that also bonded to those receptors. When scientists in the 1970s isolated a biochemical from a pituitary gland hormone that showed analgesic properties, Choh Li, a chemist from Berkeley, California, named it endorphin, meaning “the morphine within.” Besides behaving as a pain reducer, endorphins are also thought to be connected to euphoric feelings, appetite modulation, and the release of sex hormones. Prolonged, continuous exercise contributes to an increased production of endorphins and, in some people, the subsequent “runner's high.”

Etymology

Origin of endorphin

1970–75; end(ogenous) (m)orphine, with -ine respelled as -in ²

Explanation

If you’re getting sore and tired while running, don’t worry! Just wait for your endorphins to kick in. An endorphin is a hormone that your body produces to ease pain and make you feel calm and happy. Endorphins are sometimes called "natural pain killers," since that's the way they act in the body. Things like stress and exercise can stimulate the release of endorphins. A “runner’s high” happens when a runner gets a rush of endorphins. Your nervous system and pituitary gland send endorphins to your brain, where they bind to special receptors. It's similar to what happens when you take a painkilling medication. In fact, the word endorphin is a blend of “endogenous” (meaning "inside the body") and “morphine" (a medication that relieves pain).

Example Sentences

It may be a thrill show and a shallow endorphin rush, but the one thing that it isn’t is journalism, which we still happily criticize.

From Salon • Feb. 6, 2026

Zoe Giles, a 34-year-old mother of two in Kent, England, gets an endorphin rush each time a package arrives from Shein or Temu.

From The Wall Street Journal • Dec. 18, 2025

Gen Z and millennials are increasingly trading late alcohol-fuelled nights for early-morning endorphin highs to take part in run clubs and earn virtual kudos on fitness apps like Strava.

From BBC • May 2, 2025

A mutation in a gene called pro-opiomelanocortin prevents the production of a hormone and a kind of endorphin, the absence of which acts as a starvation signal.

From Science Magazine • Mar. 8, 2024

Because I make such a point of getting in my workout every day, my husband has accused me of being an endorphin junkie, and he is right!

From How and When to Be Your Own Doctor by Solomon, Steve