'Runner's high' similar to marijuana high due to endocannabinoids in the body, not endorphins: study

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The accepted preconceived notion that endorphins cause the improvement of mood after a strenuous exercise may not be right at all. A study published at the Proceedings of the National Academy of Sciences found that the "runner's high" is caused by endocannabinoids and not by the "happy hormones."

According to Medicine Net, endorphins are neurotransmitters or chemicals that pass signals from neuron to the next. They are triggered by stimuli of stress, pain or fear and can come from parts of the brain, nervous system, spinal cord or pituitary gland. Endorphin secretion can boost the improvement of mood, moderates appetite and increases the immune response. Endocannabinoids are basically the body's natural source of marijuana, and like the effects of the plants, it can decrease pain, improve appetite and elevate the mood.

The researchers from Central Institute of Mental Health of the University of Heidelberg tested on mice models using running wheels. After the exercise, they found that mice had elevated levels of endorphins and endocannabinoids. They were less anxious and have reduced pain sensitivity.

When the team blocked the mice's endocannabinoid receptors, they found that the mice have heightened pain sensitivity and just as anxious in the first place.

"These highly active rats would run on their wheels constantly," said Greg Ruegsegger, lead author from The University of Missouri, via Science Daily. "However, when we chemically activated their mu-opioid receptors, those rats drastically reduced their amounts of activity. Since exercise and addiction to substances follow this same chemical process in the brain, it stands to reason that activating these receptors in people with dangerous addictions could provide the same rewards they are craving without the use of dangerous drugs or alcohol."

"[This shows] for the first time to our knowledge that cannabinoid receptors are crucial for main aspects of a runner's high," the study authors wrote.

When the researchers conducted a similar experiment to block out the mice's opioid receptors, they found that it made no significant difference in their activity levels.

The results of the mice study cannot be said the same for humans. According to Yahoo, the mice in the experiments ran for three miles per day to acquire a runner's high and this suggests that "humans have evolved to be in motion."