Endocannabinoid signals rise during runs up to 230 km

At Lake Baldeney in Essen, 19 experienced runners completed a marathon while Dr. Michael Siebers and his team collected blood samples before the start, after 14 kilometers, 28 kilometers and approximately 43 kilometers. The body's own cannabis-like signaling molecule anandamide, or AEA, kept rising across the race and was still elevated 45 minutes into recovery.

The finding extends a line of research on the runner's high. In 2015, the University of Duisburg-Essen team reported that running's anxiety- and pain-reducing effects depend on cannabinoid receptors. A 2021 study involving 63 people found that the runner's high persisted even when the effects of endorphins were pharmacologically blocked, while endocannabinoid levels increased. Most earlier endurance studies had lasted less than 60 minutes.

The marathon runners also served as their own comparison. One to two months later, they walked the same route for the same amount of time they had previously needed to finish the marathon. Their AEA response was considerably smaller, giving the researchers a direct contrast between running and walking under similar conditions.

The team then followed 36 participants at the 2024 TorTour de Ruhr, running 100 kilometers, 160 kilometers or 230 kilometers. Blood samples taken before and after the event showed that AEA remained significantly elevated after all those distances; a second endocannabinoid, 2-AG, also increased. After finishing, runners reported less anxiety, while euphoria did not change significantly. Most participants experienced pain during the run, but five reported remaining pain-free.

Concretely, the research gives scientists a measurable endocannabinoid signal across full marathon and ultramarathon efforts, rather than only during shorter exercise sessions. It does not yet prove that AEA or 2-AG causes euphoria, reduces anxiety or changes pain perception. Siebers and Johannes Fuß say the next step is to determine precisely what role these molecules play in the runner's high.