The Runner’s High: New research shows that cannabinoids, not endorphins, are responsible – and that has important therapeutic implications

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So it’s not the endorphins after all! The runner’s high certainly exists – the mild euphoria and deep sense of relaxation you experience after 45 minutes or so of moderately intense exercise. But a clever experiment run by German researchers published this month rules out the “endogenous opioids” (endorphins) and says it’s the endocannabinoid system that’s responsible: “this study indicates that the development of a runner’s high does not depend on opioid signaling in humans, but makes eCBs [endocannabinoids] strong candidates.”

They took 63 experienced runners, male and female, and divided them into 2 groups. The controls simply ran on a treadmill for 45 minutes and most experienced a runner’s high. The other half, the experimental group – and this is the neat part – were given a drug, naltrexone, that blocks the uptake of endorphins in the brain; i.e., if this group says they experienced a runner’s high it couldn’t have had anything to do with their internal opioid system because it was inactivated by naltrexone.

Result: An equal number of people in the experimental and control groups experienced a runner’s high.

So why did the opioid-inactivated experimental group still experience a runner’s high? The authors give 3 reasons: It’s understood that exercise leads to the release of eCBs, which they characterize as “rewarding” molecules; after running, both the control and experimental groups had higher plasma levels of the eCBs anandamide (AEA) and 2-arachidonoglycerol (2-AG); and, this study builds on the authors earlier work with mice that showed directly that a runner’s high depends on cannabinoids, not opioids.

In fact, the mice study was even stronger because there they were able to administer a drug that inactivated the endocannabinoid system with the result that the mice did not show signs of the runner’s high as measured by their decreased tolerance to light stimuli (which measures anxiety) and to standing on a hot plate (measuring pain and stress). (This inactivating drug is not permitted to be used in humans).

This study matters because it demonstrates, especially to the uninitiated, the biological activity of the eCB system. More importantly, notice what the system does – it’s directly involved in the modulation of pain, stress, and anxiety, and can yield a mild sense of euphoria. Thus lending credence to the multitudes of people the world over who use cannabinoids for exactly those reasons.

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