A marathon, 100 kilometers or even 230 kilometers in one go: Anyone running such distances puts enormous strain on their body. At the same time, levels of the body’s own cannabis-like signaling molecules rise significantly. Dr. Michael Siebers from the Institute of Forensic Psychiatry and Sex Research at the University of Duisburg-Essen and his team have, for the first time, tracked in greater detail how these so-called endocannabinoids develop over the course of an entire marathon and during extreme ultramarathon distances. The study has been published in BMC Medicine.
Dr. Michael Siebers is part of the research group led by Prof. Dr. Johannes Fuß, which has been studying the runner’s high for many years. In 2015, the team showed that the anxiety- and pain-reducing effects of running depend on cannabinoid receptors. A study involving 63 people demonstrated in 2021 that the runner’s high still occurs when the effects of endorphins are pharmacologically blocked. At the same time, endocannabinoid levels increased. This suggested that endocannabinoids play an important role in the phenomenon.
Previous studies, however, had mainly examined endurance exercise lasting less than 60 minutes. The current study took a different approach: For the first part of the investigation, 19 experienced runners completed a marathon around Lake Baldeney in Essen,Germany. The researchers took blood samples before the start and after 14, 28 and approximately 43 kilometers, with a final sample taken after 45 minutes of recovery. For comparison, the same participants returned one to two months later and walked along the same route for the same amount of time they had previously needed to complete the marathon. The body’s own cannabis-like signaling molecule anandamide, or AEA, showed a particularly marked response.
“We found that anandamide does not only increases at the beginning of a run. Its concentration continues to rise over the course of an entire marathon, and levels are still elevated even 45 minutes later. During walking, the change was considerably smaller,” says Dr. Michael Siebers, who led the study.
Conditions were even more extreme in the second part of the study: 36 participants in the 2024 TorTour de Ruhr ran distances of 100, 160 or 230 kilometers. The researchers took blood samples before and after the race. AEA levels were significantly elevated even after these distances. A second endocannabinoid, 2-AG, also increased. At the same time, the ultramarathon runners reported less anxiety after finishing, whereas euphoria did not change significantly. Most participants reported experiencing pain during the run, while five said they remained pain-free. “The study therefore provides new insights into the biological processes behind extremely long-distance running,” explains Siebers, who is a runner himself.
“Our current findings show that the endocannabinoid system remains active even during very long runs,” says Prof. Dr. Johannes Fuß. “However, we cannot yet conclude from these results that the signaling molecules are actually responsible for the runner’s high. To establish that, we need to determine more precisely what role they play in euphoria, anxiety reduction and pain perception during running.”
* The study was supported by the Medical Faculty of the University of Duisburg-Essen and the Stiftung Universitätsmedizin Essen (Essen University Medicine Foundation).
Publication: https://link.springer.com/article/10.1186/s12916-026-05186-z
Further information:
Dr. Michael Siebers, Institute of Forensic Psychiatry and Sex Research, michael.siebers@lvr.de
Prof. Dr. Johannes Fuß, Director of the Institute of Forensic Psychiatry and Sex Research, johannes.fuss@uni-due.de