Updated: Apr 2
A 2021 study entitled "Exercise-induced Euphoria and Anxiolysis do not Depend on Endogenous Opioids in Humans" that was published in the journal Psychoneuroendocrinology explored the phenomenon of exercise euphoria commonly called runner's high that has traditionally been attributed to the endogenous (internally produced) pain killer endorphin.
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What is Runner's High?
The study described the runner's high phenomenon as "a sense of well-being during endurance exercise characterized by euphoria and anxiolysis [anxiety reduction]. It has been a widespread belief that the release of endogenous opioids, such as endorphins, underlie a runner's high."
The study noted that exercise leads to the release of two classes of "rewarding molecules," endocannabinoids (such as 2-AG and anandamide) and opioids (such as endorphin).
In preclinical studies involving rodents, "we have shown that core features of a runner's high depend on cannabinoid receptors, not opioid receptors." The researchers behind this study had the goal of revealing the source and underlying mechanism of runner's high with human study subjects.
Exercise Produces Endocannabinoids
The study gathered data on 63 participants who "exhibited increased euphoria and decreased anxiety after 45 min of running on a treadmill in a moderate-intensity range." The study's authors described how running resulted in higher levels of the endocannabinoids 2-AG and anandamide.
To test the effect of the endocannabinoids on euphoria and anxiety levels, opioid blockers were employed. The study revealed that this opioid blockage did not prevent the development of euphoria and reduced anxiety, including "elevation of endocannabinoid levels following exercise."
To test the effect of the endocannabinoids on euphoria and anxiety levels, opioid blockers were employed. The study revealed that this opioid blockers did not prevent the development of euphoria and reduced anxiety in study participants, nor did it prevent "elevation of endocannabinoid levels following exercise."
This study indicates that the development of a runner's high does not depend on opioid signaling in humans, but instead results from the production of endocannabinoids such as 2-AG and anandamide. While this dynamic had been revealed previously in rodent models, this study was the first to validate endocannabinoids as the source of runner's high via a controlled study of humans.
View the original study.
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