A first-of-its-kind study, published in the journal BMC Medicine, has found that long-distance running can lead to an increase in the amount of THC-like molecules in the body.
Researchers at the University of Duisburg-Essen found that levels of anandamide – an endocannabinoid sometimes called the “bliss molecule” – increased throughout a marathon and were still raised 45 minutes after runners had finished. The rise was much smaller when the same people walked the same route for the same amount of time.
Runner’s high is a feeling described as one of euphoria and calmness mixed with reductions in anxiety and pain, and is experienced by people who enjoy endurance sports. Until recently, it was believed endorphins caused the phenomenon, but it is now widely believed that endorphins cannot cross the blood-brain barrier.
Endocannabinoids are molecules the body makes naturally. They act on the same signalling system as cannabis compounds, but are not derived from cannabis, nor is there evidence that runners are somehow producing THC.
Anandamide (AEA) has a similar composition and produces the same calming and euphoric effects as the high associated with the THC produced from consuming cannabis.
Other endocannabinoids released during endurance sports include 2-arachidonoylglycerol (2-AG) and 1-arachidonoylglycerol (1-AG).
To understand the link between running and endocannabinoids, researchers conducted two studies. The first involved 19 experienced runners completing a marathon around Lake Baldeney in Essen, Germany. Researchers took blood samples before the start, after 14km and 28km, at the finish and again after 45 minutes of recovery. Runners were asked to abstain from eating or drinking anything containing caffeine, to avoid nicotine products for the whole day prior, and were instructed not to run during the previous 24 hours. Runs were scheduled at the weekend to coincide with lower levels of cortisol.
One or two months later, the same participants returned to walk the same course. Their walks were matched to the time each had taken to finish their marathon, allowing the team to compare running with a lower-intensity activity over the same duration.
AEA rose progressively over the marathon and remained elevated during recovery. A second endocannabinoid, 2-AG, rose later in the marathon. Both changes were more marked during running than walking.
The second part of the research followed 36 competitors in the 2024 TorTour de Ruhr, who raced 100km, 160km or 230km. Runners in this cohort were also instructed to abstain from caffeine and nicotine and screened, but less vigorously, as their study was set within a competitive environment. Blood tests taken before and after the races again showed higher AEA levels after the runners had finished. Levels of 2-AG also rose after the ultramarathons.
“Our findings show robust and time-dependent changes in circulating [endocannabinoid] levels during prolonged endurance exercise,” the researchers wrote.
During the marathon, participants reported more euphoria and lower anxiety than during the walking session, particularly towards the end of the route. Among ultramarathon runners, anxiety fell after the race, while euphoria did not change significantly. Pain, meanwhile, increased substantially during the longer races.
However, when asked, only three of the 19 marathon runners said they experienced a runner’s high during their race. Twelve of the 36 ultramarathon runners reported one, while 19 said they did not. “No formal definition of the runner’s high was provided, and responses were therefore based on participants’ individual understanding of the concept,” the study said, making that result difficult to interpret.
The researchers say that while the findings show an association between prolonged running, higher levels of endocannabinoids and some changes in mood, they do not demonstrate that AEA or 2-AG directly cause the runner’s high. They added that future research will need to explore how these molecules interact with brain signalling and other chemicals involved in exercise.