Endorphins

What are Endorphins?

Endorphins are naturally occurring peptides produced in the brain and pituitary gland. Often called the body's natural painkillers, they act at opioid receptors and help regulate pain. They also participate in reward, mood and stress responses.

Examples of endorphins

Beta-endorphin is a well-studied example, produced from the precursor proopiomelanocortin (POMC). It occurs in a full-length form and shorter processed forms. As Fricker and colleagues explain, “endorphins” should not be used as a catch-all name for every opioid peptide made by the body.

How they work

Endorphins bind to opioid receptors, the same family of receptors acted on by drugs such as morphine. This can reduce the perception of pain. Their effects depend on where they are released and what is happening in the body; a higher blood level does not automatically mean someone feels less stressed.

What about a runner's high?

Endorphins get much of the credit for exercise-induced euphoria. The evidence is more interesting than that familiar story. In a double-blind study of 63 participants, Siebers and colleagues (2021) found that exercise-related euphoria and anxiety reduction persisted when opioid receptors were blocked with naltrexone.

That result challenges the idea that endorphins are necessary for a runner's high. It does not settle every mechanism involved in exercise, but it gives us a good reason to stop treating “endorphins” as a complete explanation for why a run can feel good.