Some describe it as euphoria. Others as calm, clarity or even a sense of being completely absorbed in the moment. Many people experience some version of it after a long run. For years, scientists believed the phenomenon was caused by endorphins, the body’s natural opioids, but recent neuroscientific research indicates this might not wholly be the case.
Endorphins cannot cross the blood-brain barrier—the tightly regulated system that protects the brain from substances in the bloodstream. So while endorphins may well contribute to pain relief elsewhere in the body, they cannot fully explain the feelings of euphoria and emotional wellbeing generated by a runner’s high within the brain itself.
Exercise activates the Endocannabinoid System (ECS). Endocannabinoids are naturally produced by our bodies. They help with functions such as pleasure, memory and stress regulation. One of the most important chemicals produced by the ECS is anandamide. It helps reduce anxiety, ease pain and create feelings of calm and wellbeing.
Researchers found that levels of anandamide—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. Unlike endorphins, anandamide crosses the blood-brain barrier with ease.
Anandamide activates cannabinoid receptors in regions involved in emotion, motivation, reward and pain perception. The resulting effects are remarkably similar to many features of the runner’s high, including reduced anxiety, better movement, less pain and feelings of calm.
“Our findings show robust and time-dependent changes in circulating [endocannabinoid]
levels during prolonged endurance exercise”, researchers wrote.
This isn’t to suggest that endorphins play no role in a runner’s high. Modern neuroscience suggests endorphins and endocannabinoids work together, with endocannabinoids probably playing the larger role in producing the emotional aspects of the experience.
Several other neurotransmitters also play a part in a runner’s high. Dopamine, which is central to motivation and reward, helps reinforce actions that are beneficial for survival. Rather than simply producing pleasure, dopamine encourages us to repeat a behaviour that the brain considers valuable. Serotonin contributes to emotional stability and wellbeing, while noradrenaline enhances alertness and focus.
For those who want to chase after a runner’s high, research suggests there’s a sweet spot to achieving it and it doesn’t require long-distance, extreme endurance. Most studies report increases in endocannabinoids after approximately 30 to 60 minutes of continuous aerobic exercise performed at moderate to vigorous intensity—so roughly 70-85% of maximum heart rate. The key is that the physiological stress is high enough to trigger these neurochemical responses without overwhelming the body.
That said, there is considerable individual variation. Although one survey found that around two-thirds of recreational runners had experienced a runner’s high at least once, it didn't necessarily happen on every run. Some people also appear naturally more responsive to exercise-induced endocannabinoid release. Genetics, sex, fitness level, sleep quality, psychological state and even expectations may all influence whether someone experiences runner’s high on any given day, too.
“Our findings suggest that changes in circulating endocannabinoid concentrations may represent an important physiological feature of prolonged endurance exercise in humans and occur alongside affective changes to potentially promote long-distance running”.