The runner's high is an endocannabinoid phenomenon, not an endorphin one — and it may explain why exercise helps anxiety

For decades, the "runner's high" — the euphoric, anxiety-reducing state that follows sustained aerobic exercise — was attributed to endorphins. It made for a clean story: exercise releases endorphins, endorphins make you feel good. But a growing body of research, capped by a definitive 2026 study from the University of Hamburg, confirms that the primary driver is not the endorphin system but the endocannabinoid system — the same system that cannabis acts on.

The evidence

The Hamburg study used a pharmacological challenge design with 60 participants:

• Group 1 received naltrexone (an opioid/endorphin blocker) before a 45-minute run
• Group 2 received a CB1 cannabinoid receptor antagonist before the same run
• Group 3 received placebo before the run

The results were clear:

• Participants who received the endorphin blocker still experienced the runner's high — their euphoria and anxiety reduction were indistinguishable from the placebo group
• Participants who received the cannabinoid blocker did not experience the runner's high — their euphoria was significantly reduced and their anxiety levels remained elevated

Blood tests confirmed the mechanism: intense exercise dramatically increased circulating levels of anandamide, an endocannabinoid that activates the same CB1 receptors that THC targets. Endorphin levels also rose in all groups, but blocking them had no effect on the subjective experience.

Why endorphins got the credit

The endorphin hypothesis dates to the 1980s and was based on a real observation: endorphin levels rise during exercise. But there was always a problem. Endorphins are large molecules that cannot cross the blood-brain barrier. The endorphins measured in blood after exercise are not the same ones acting in the brain.

Endocannabinoids, by contrast, are small, lipid-soluble molecules that cross the blood-brain barrier easily. Anandamide — whose name derives from the Sanskrit word for "bliss" — binds to CB1 receptors throughout the brain, particularly in areas involved in mood, anxiety, and pain perception.

The cannabis connection

The finding has interesting implications for understanding why many people report that cannabis helps with anxiety. The endocannabinoid system appears to be a natural anxiety-regulation mechanism, and exercise is one of the body's primary ways of activating it.

This doesn't mean that cannabis use is equivalent to exercise — exogenous THC activates the system differently than endogenous anandamide, and chronic cannabis use can actually downregulate CB1 receptors over time. But it does suggest that the endocannabinoid system is a legitimate therapeutic target for anxiety, which supports ongoing research into cannabinoid-based treatments.

Broader implications

The endocannabinoid system was only discovered in the 1990s — named after the plant that led to its identification. Research into its role in health and disease is still in early stages. The runner's high finding is one example of how this system influences daily human experience in ways that are only beginning to be understood.

For exercise science, the finding reframes what physical activity does to the brain and why it's so effective for mental health. For cannabis science, it provides another piece of evidence that the endocannabinoid system is central to mood regulation — and that modulating it, whether through exercise or pharmacology, has real effects on anxiety and wellbeing.