A new study suggests that endorphins may have nothing at all to do with the so-called runner’s high. Instead, these warm fuzzy feelings may be the result of chemical compounds made by the body called endocannabinoids. The endocannabinoid system is also responsible for moderating the psychoactive, feel-good effects of marijuana, The New York Times reports.
Endorphins are the body’s natural painkillers. Back in the 1980s, scientists found that endorphin levels in the blood spiked after prolonged exercise. From there, people made the logical leap to assume that these chemicals also produced the sense of euphoria in the brain. But there’s a problem with this theory. Endorphins are big molecules, and are too large to fit through the brain’s gatekeeper - the blood-brain barrier. So there’s no way they could be responsible for the post-run high.
Researchers have spent the last decade looking for other explanations, which led them to cannabinoids."