These scientists believed that endocannabinoids were more of a drug. Similar to the chemical structure of cannabis, the number of cannabinoids produced by our bodies is increasing during pleasant activities, such as orgasms, and also when we run, studies show. They can also cross the blood-brain barrier, making them viable candidates to raise a runner.
A few experiments in the past have strengthened the possibility. In one notable study from 2012, researchers lured dogs, humans, and ferrets to run on careers while measuring their blood levels of endocannabinoids. Dogs and humans are tentative, meaning they possess legs and muscles that are well adapted for distance running. Ferrets are not; they sneak and jump, but rarely walk descending miles, and they do not produce extra cannabinoids while running the treadmill. The dogs and humans did, however, indicating that they most likely experienced a runner height and that it could be traced back to their internal cannabinoids.
However, the study does not exclude a role for endorphins, as dr. Johannes Fuss realized. The director of the human behavior laboratory at the University Medical Center Hamburg-Eppendorf in Germany, he and his colleagues have long been interested in how different activities affect the inner workings of the brain, and after reading the ferret study and others, thought to take a closer look in the runner’s climax.
They started with mice, who are keen runners. For a 2015 study, they chemically blocked and allowed the uptake of endorphins into the animals’ brains, and then did the same with the uptake of endocannabinoids. When their endocannabinoid system was shut down, the animals ended their runs just as anxiously and creepily as at the beginning, indicating that they felt no runner. But when their endorphins were blocked, their behavior after running was calmer, relatively more blissful. They seem to have developed the familiar, soft buzz even though their endorphin systems were inactivated.
Mice are definitely not humans. Thus, for the new study, published in February in Psychoneuroendocrinology, dr. Fuss and his colleagues try to repeat the experiment, as far as possible, in humans. They recruited 63 experienced runners, male and female. They invited them to the lab, tested their fitness and current emotional states, drew blood and randomly assigned half to receive naloxone, an opioid-blocking drug, and the rest a placebo. (The drug they used to block endocannabinoids in mice is not legal in humans, so they could not repeat the part of the experiment.)