The real cause of "Runner's High" may surprise you. It'll surprise you less if you smoke pot.

Endorphins may have been getting too much credit for "runner's high," that euphoric lift we get when we exercise intensely.

According to a new experiment using lab mice as models, "The findings suggest that endorphins have little to do with runner's high." 

That euphoric exercise rush "may be the product of a completely different but oddly familiar substance — the body's own endocannabinoids, the chemicals that, like the cannabinoids in marijuana, lighten mood."

Screen Shot 2015-10-07 at 4.16.32 PM

From the New York Times:

Endocannabinoids are, essentially, internally produced marijuana, or cannabis. Cannabis contains cannabinoid molecules, which are small enough to cross the blood-brain barrier and attach there to receptors, producing a floaty, hey-dude high.

In recent years, scientists have found that exercise raises the levels of endocannabinoids in the bloodstreams of people and animals, making these molecules good candidates to underlie the runner's high.

But few studies have directly compared the effects of endorphins and endocannabinoids to determine which really makes exercise mildly intoxicating.

The results of the new study, published this week in Proceedings of the National Academy of Sciences, are available here. Researchers from the University of Heidelberg's Central Institute of Mental Health tested the anxiety levels of healthy lab mice, then gave them running wheels.

"In general, these post-running mice were more chill than before."

When researchers gave the mice endocannabinoid blockers, that chill vanished.

More in Gretchen Reynold's writeup at the Times: "Homing In on the Source of Runner's High," or in the PNAS.