A new study conducted at the Georgia Institute of Technology and the University of California, Irvine suggests that a class of chemicals known as cannabinoids may be the missing piece of the "runner's high" puzzle long sought by scientists.

"Exercise is good for the mind. For the millions of people who exercise, this is not a secret," said Arne Dietrich, the study's principal investigator and a former visiting professor at Georgia Tech. "It helps reduce stress, lowers anxiety, suppresses pain, produces a feeling of well-being and can even lead to a euphoric state. To scientists, however, the process that leads to this last phenomenon -- popularly known as the 'runner's high' -- remains an elusive mystery."

A critical clue in the mystery may have been found, however. As published recently in the journal Neuroreport, Dietrich's research team has found very high levels of a naturally occurring cannabinoid called anandamide in runners and cyclists who exercised at moderate intensity for an extended period.

Anandamide produces effects similar to those of THC, the psychoactive constituent of marijuana, leading researchers to speculate that "runner's high" may not be caused by endorphins released by the human body - as previously thought -- but by a naturally occurring cannabinoid high.

"I was aware of the limitations of the endorphin theory for explaining the runner's high, and I thought that Dr. Dietrich's novel hypothesis fit well within recent endocannabinoid discoveries," said Professor Phil Sparling, co-director of the Exercise Physiology Lab and Dietrich's host at Tech..

"The body's ability to produce cannabinoids is currently an intense area of research", said Dietrich, who studied them as a visiting professor in Georgia Tech's School of Applied Physiology this past year. His one-year stay at the Institute was made possible through the College of Sciences Faculty Development Program.

"Cannabinoids that are produced naturally by the body are called endocannabinoids," Dietrich said. "The body's endocannabinoid system has evolved primarily for pain modulation -- that is, pain or stress activates the system naturally. This activation, in turn, helps the body to modulate the pain."

"This natural analgesic system is independent of and complimentary to the body's opioid system," he said, and it performs other natural functions such as vasodilation, bronchodilation and sedation.

"Because anandamide and THC bind to the same receptor in the body, all these are also primary effects of smoking or ingesting cannabinoids from outside the body," Dietrich said.

For their study, researchers asked 24 young men to either run, cycle or sit. If they ran or cycled, participants began with a five-minute warm-up, then built up to a 70-80 percent heart rate, which they sustained for 45 minutes, followed by a cool-down.

In those subjects, investigators documented a dramatic endocannabinoid increase in their body, providing the first evidence that exercise activates the endocannabinoid system. "Numerous follow-up studies are necessary to understand the precise nature of this increase," Dietrich said, but it remains an exciting discovery for him and his team.

"Since exercise is physical stress -- albeit healthy stress -- and because it produces muscle break-down, I thought exercise might activate it. This is what we found," he said. "No other study has ever considered this possibility, which is why the results are so significant."

Dietrich believes the human body begins to produce high levels of endocannabinoids - and thus a natural "runner's high" -- during moderate-to-intense exercise that produces prolonged stress and pain.

"Once the endocannabinoid system is highly activated, it causes a naturally induced high, as the endocannabinoids produce the same effect than when it is activated unnaturally -- by smoking THC for instance," he said.

It does not appear that this effect causes any harm to runners and athletes who experience it after intense exercise, however.

"In exercise, there is a reason why the endocannabinoid system is activated," Dietrich said. "One has to deal with a physical stressor, and the endocannabinoid system fulfills its purpose. Smoking marijuana is a different story. This is an unnatural abuse of the system - not intended to be used this way by evolution."

Dietrich believes this study might provide a possible mechanism to explain why the "runner's high" might be caused, and it suggests that exercise might be useful to help in the treatment of chronic pain or glaucoma, both of which are treated in some parts of the country in clinical experimental trials using plant-derived cannabinoids such as THC.

"Our work raises many questions," Dietrich said. "We need to characterize which types of exercise best activate the system, at what intensity, and at what duration," he said.

"We also need to know: Are there sex differences? Why and when is the system overwhelmed? Can it be used to maximize performance in some way? How does this effect decision making - for example, at the end of a marathon race, or in a combat situation? Our findings produce entirely new avenues of research never considered previously," he said.

Dietrich is an assistant professor of psychology at Georgia College and State University in Milledgeville, where he also directs the Department of Psychology's Behavioral Neuroscience Laboratory. His experience at Georgia Tech was part of the College of Sciences Faculty Development Program, which Dean Gary Schuster said provides an exciting way for the Institute to help advance science throughout the state.

"The whole idea here is that Georgia Tech has resources available to it that some other institutions in the University System of Georgia do not, and faculty members at those institutions need to stay current in their disciplines just as much as ours do," Schuster said. "After all, only people who are active in their disciplines can transmit that excitement and inspiration to their students."

The Faculty Development Program provides an opportunity for other University System of Georgia faculty to spend either a semester or a year at Georgia Tech, collaborating on research and teaching students.

"It adds a new perspective to some of our courses, and it establishes a connection between us and other universities in Georgia," Schuster said. "I think it gives Georgia Tech a very positive way to contribute to research and teaching throughout the university system."