Endocannabinoids are a more likely intoxicant, these scientists believed. Similar in chemical structure to cannabis, the cannabinoids that our body produces increase in number during pleasant activities such as orgasms and also while running, as studies show. They can also cross the blood brain barrier, making them suitable candidates for causing a runner high.
Some previous experiments had reinforced this possibility. In a notable 2012 study, researchers persuaded dogs, humans, and ferrets to run on treadmills while measuring their blood endocannabinoid levels. Dogs and humans are volatile, which means they have bones and muscles that are good for distance running. Ferrets aren’t; They sneak and sprint, but rarely cover miles or produce extra cannabinoids while running on the treadmill. However, the dogs and humans stated that they most likely had a runner high and this was due to their internal cannabinoids.
However, this study did not rule out a role for endorphins, as Dr. Johannes Fuss recognized. The director of the Laboratory for Human Behavior at the University Medical Center Hamburg-Eppendorf in Germany and his colleagues had long been interested in how various activities affect the inner workings of the brain and had thought after reading the Ferret Study and others that it might be possible Take a closer look at the height of the runner.
They started with mice who are avid runners. For a 2015 study, they chemically blocked the uptake of endorphins in the animals’ brains and let them go. Then they did the same thing with ingesting endocannabinoids. When their endocannabinoid system was turned off, the animals ended their runs just as anxious and nervous as they were at the beginning, indicating that they had not felt high. But when her endorphins were blocked, her behavior after running was calmer and relatively blissful. They seemed to have developed that familiar, mild hum even though their endorphin systems had been inactivated.
However, mice are emphatically not humans. For the new study, published in Psychoneuroendocrinology in February, Dr. Fuss and his colleagues set about repeating the experiment on humans as much as possible. They recruited 63 experienced runners, men and women, invited them to the lab, tested their fitness and current emotional states, took blood and randomly assigned half to receive naloxone, a drug that blocks the absorption of opioids, and the rest, a placebo. (The drug they used to block endocannabinoids in mice isn’t legal in humans, so they couldn’t repeat this part of the experiment.)