The Molecule of Bliss What Really Powers the Runner’s High?
The runner’s high has always sounded almost mysterious.
Someone exercises for a long time, gets tired and uncomfortable, and then suddenly feels calmer, lighter or unusually focused. Sometimes the discomfort seems less important. For some people, exercise even leaves them with a sense of well-being that lasts beyond the workout.
For years, the standard explanation was simple: endorphins.
But exercise scientists now believe the story is more complicated.
One of the most closely studied alternatives is the endocannabinoid system, a network of chemical messengers and receptors involved in pain, mood, stress, appetite and other processes. Among these messengers is anandamide, a lipid molecule whose name comes from a Sanskrit word associated with joy or bliss.
And new research published in 2026 is giving scientists an unusually detailed look at what happens to these molecules during very long-distance exercise.
A new look at an old mystery
Researchers from the University of Duisburg-Essen studied experienced runners during a marathon and also examined participants completing ultramarathon distances of 100, 160 and 230 kilometers.
In the marathon portion, 19 runners provided blood samples before the race and at several points during and after it. Anandamide levels rose as the marathon progressed and remained elevated 45 minutes after finishing. The increase was considerably smaller during a comparable period of walking.
In the ultramarathon group, which included 36 participants, both anandamide and another endocannabinoid called 2-AG were elevated after the races. The runners also reported less anxiety after finishing, although their reported euphoria did not significantly change.
That last detail is important.
The researchers did not conclude that anandamide has been proven to cause the runner’s high. Instead, they say the findings provide new evidence that the endocannabinoid system remains active during prolonged exercise and deserves further investigation.
So what happened to endorphins?
Endorphins are still part of the story.
They are naturally produced opioid peptides involved in pain regulation and stress responses. But the old idea that exercise simply causes endorphins to flood the brain and create the entire runner’s high has become difficult to support.
One reason is that circulating beta-endorphins do not readily cross the blood-brain barrier. Researchers therefore began looking more closely at other systems that could help explain the emotional changes associated with exercise.
A systematic review of human studies found that most investigations of acute exercise detected increases in endocannabinoids. However, the authors also emphasized that human evidence was not yet strong enough to prove that these molecules directly cause the runner’s high.
That distinction matters: an association is not the same as proof of cause and effect.
Meet anandamide
Anandamide is one of the body’s naturally occurring endocannabinoids. It interacts with cannabinoid receptors, particularly CB1 receptors, which are widely distributed throughout the nervous system.
Because anandamide is a lipid messenger, it behaves differently from peptide hormones such as endorphins. It is produced and broken down relatively quickly, allowing the body to adjust signaling according to changing conditions.
Exercise appears to influence this system, particularly during aerobic activity.
Researchers have proposed that endocannabinoid signaling may contribute to several experiences associated with exercise, including changes in pain perception, anxiety and mood. A previous meta-analysis found generally consistent increases in anandamide after acute exercise, although the size of the response varied substantially between studies.
It is probably not just one molecule
The most interesting lesson may be that the runner’s high is not a single-chemical phenomenon.
Anandamide may be one important player, but dopamine, serotonin, endorphins and other signaling systems also participate in how the brain responds to physical activity.
That makes sense when you think about the experience itself.
Exercise can change how a person perceives pain, regulate stress responses, affect motivation and influence mood. Expecting one molecule to explain all of those effects is probably too simplistic.
The 2026 marathon research strengthens the case for endocannabinoids, but it does not eliminate the possibility that several biological systems are working together.
What does this mean if you are older?
You do not need to run a marathon—or anything remotely close to one—to benefit from physical activity.
That is particularly important for older adults.
Research on physical activity in later life consistently focuses on practical benefits such as maintaining physical function, supporting quality of life and helping people remain independent. An umbrella review involving older adults found evidence that physical activity and exercise programs can influence health-related quality of life.
The goal, therefore, should not be chasing an extreme physiological state.
A brisk walk, comfortable cycling session, swimming workout, dancing or another activity you can perform safely may provide meaningful benefits without the enormous physical stress of an ultramarathon.
And if you have heart disease, significant joint problems, balance difficulties, or another medical condition, it is sensible to discuss an appropriate exercise level with your healthcare professional before substantially increasing activity.
The surprising takeaway
The runner’s high is becoming less mysterious—not because scientists have discovered one magical “bliss molecule,” but because research is revealing a much more sophisticated conversation between the brain and body.
The latest findings show that prolonged running can produce striking changes in naturally occurring endocannabinoids, particularly anandamide. But researchers are still working out exactly how those changes translate into feelings of calm, reduced anxiety, altered pain perception or euphoria.
That uncertainty actually makes the discovery more interesting.
Exercise does not simply tire the body and then somehow make the brain feel better afterward. It triggers a complex biological response involving multiple signaling systems.
And somewhere within that conversation, anandamide appears to have an important part to play.
The next time physical activity leaves you feeling unexpectedly clear-headed or calm, there may be a fascinating explanation unfolding beneath the surface—but scientists are still discovering exactly how all the pieces fit together.
Photo by Tirachard Kumtanom: https://www.pexels.com/photo/woman-about-to-run-during-golden-hour-347134/
About Wellcore Weekly: Wellcore Weekly covers health, wellness, nutrition, sleep, fitness, and medical research with timely, easy-to-understand updates for everyday readers.
