The real science behind runner's high, and why women feel it more intensely. P.s It’s not endorphins.
I experience runner's high on almost every run, regardless of distance or duration. Well mostly anyway. After a while I started to feel almost guilty about it, like I had somehow stumbled into a biological lottery that most people don't win. So I went looking for the science behind what was happening on a cellular level.
What I found was that the story we've been told for decades is almost entirely wrong. Like many things…
That post-run glow, the euphoria, the reduced pain, the specific tranquillity that makes early morning kilometres feel worthwhile, has been attributed to endorphins since the 1980s. You have proabably heard that story at some point. It is also, according to the current neurobiological evidence, almost certainly a myth.
Research suggests that only 69 to 77% of runners have ever experienced a true runner's high. If you have wondered why it sometimes doesn't arrive despite doing everything right, the answer lies in a system your body has been running in the background this whole time: your endocannabinoid system.
Why endorphins probably aren't responsible
The endorphin hypothesis has been repeated so often that it feels like established fact. The scientific support for it, though, is surprisingly thin, and the reason comes down to basic biology.
The blood-brain barrier is a selective membrane that acts as a filter between your bloodstream and your brain tissue. It blocks large, water-soluble molecules from crossing into brain tissue while allowing smaller, fat-soluble compounds through freely. Endorphins are large and water-soluble. They cannot cross the blood-brain barrier in meaningful quantities, which means they cannot reach the brain regions responsible for mood, reward, and pain perception. They are poor candidates for producing a psychological experience.
Endocannabinoids are structurally different. They are lipophilic (fat-loving) molecules that move through the blood-brain barrier with ease, reaching exactly the brain regions where mood and reward are regulated. A 2023 systematic review analysing the full body of human research on this question was direct: "The endorphin hypothesis was poorly supported by evidence, although it was widely perpetrated by the media" (Siebers, Biedermann and Fuss, Neuroscientist, 2023).
A separate 2023 study found that when researchers blocked opioid receptors in human subjects entirely, the euphoric effects of running remained unchanged. The endocannabinoid system was producing the experience all along (Matei et al., International Journal of Molecular Sciences, 2023). I think that’s pretty cool.
The molecules doing the actual work
Your endocannabinoid system relies primarily on two molecules: anandamide (AEA) and 2-arachidonoylglycerol (2-AG). These bind to CB1 and CB2 receptors throughout the body and brain. If CB1 sounds familiar, it is the same receptor that THC, the active compound in cannabis, binds to.
The name anandamide comes from the Sanskrit word ananda, meaning bliss, which tells you something about what it does. Research consistently shows a robust spike in anandamide following moderate-intensity aerobic exercise, and once it crosses the blood-brain barrier it modulates the reward and anxiety pathways that produce the sedation and euphoria we associate with runner's high. Your long run is, in a very literal neurobiological sense, a way to get naturally stoned. That is certainly not why I do it, but it does explain rather a lot.
Beyond the immediate feeling, endocannabinoid release during exercise contributes to reduced anxiety and stress reactivity, increased pain tolerance, improved emotional resilience that persists well after the workout ends, and enhanced focus and working memory in the hours following exercise. Personally, I feel like my bones are made of rubber and air and I am the happiest version of myself. The science supports that experience entirely.
Why intensity and duration both matter
Triggering this response requires hitting what you might think of as a biological threshold: an intensity that is neither too easy nor too demanding.
A 2023 systematic review analysing 21 human studies found that anandamide and 2-AG levels rise significantly during aerobic exercise performed at moderate intensity, roughly 70 to 85% of your age-adjusted maximum heart rate, sustained for at least 20 to 30 minutes (Siebers, Biedermann and Fuss, Neuroscientist, 2023). My own experience aligns with this precisely. The high tends to arrive around the 20-minute mark, fairly reliably.
To find your target zone, subtract your age from 220 and multiply by 0.70 for the lower end of the range. Below 50% of maximum heart rate, the body typically does not trigger meaningful anandamide release. Above 90%, the system is under a different kind of stress and the response shifts accordingly. The zone where you are working hard enough to breathe deeply but could sustain the effort for an extended period is the zone you are looking for. Steady running, rhythmic cycling, and brisk walking all fit this profile. High-intensity interval training produces different hormonal responses, beneficial in other ways, but not particularly effective for endocannabinoid release. This I can confirm from personal experience.
Duration matters as much as intensity. The system does not respond well to short bursts. Brief intense sessions may leave you feeling accomplished, but the endocannabinoid release requires time: at least 20 to 30 minutes of sustained effort before levels begin to climb meaningfully.
Why women feel this more strongly
The research becomes particularly interesting for women specifically.
A 2024 study tracking endocannabinoid levels after a 60-minute outdoor run found that women showed significantly higher increases in anandamide concentrations compared to men following the same exercise protocol (Weiermair et al., Sports, 2024). Both sexes experienced elevated endocannabinoids and improved mood post-run, but the magnitude of the anandamide elevation was notably greater in female participants. The AEA response was sex-specific, with women demonstrating a more pronounced rise. I love that for us.
This is consistent with broader research showing that the endocannabinoid system exhibits clear sexual dimorphism: it functions differently in male and female bodies. Women show greater sensitivity to cannabinoid signalling, both from endogenous molecules produced during exercise and from external cannabinoids (Craft, Life Sciences, 2012).
Estrogen appears to be the mechanism behind this difference. It enhances endocannabinoid signalling through several pathways simultaneously: increasing the density of CB1 receptors in the brain, modulating the enzymes that synthesise and break down endocannabinoids, and influencing how readily these molecules bind to their receptors (Brents, Yale Journal of Biology and Medicine, 2016). Higher estrogen means a more sensitive and responsive endocannabinoid system, which translates directly into a more pronounced runner's high.
How your cycle shapes your experience of exercise
Endocannabinoid system activity does not remain constant across the menstrual cycle. Research examining endometrial tissue has confirmed that the genes controlling endocannabinoid synthesis, degradation, and receptor expression fluctuate predictably with hormonal changes across the cycle (Tanaka et al., Cannabis and Cannabinoid Research, 2024; Montgomery et al., Scientific Reports, 2022).
During the follicular phase, when estrogen rises steadily from menstruation through ovulation, CB1 receptor expression increases across multiple tissues, the enzymes that synthesise anandamide become more active, and the enzymes that break it down become less active. The net effect is higher circulating endocannabinoid levels and greater receptor sensitivity. This is when many women report that workouts feel more manageable, recovery is faster, and the post-exercise mood lift is more pronounced. That experience is not psychological. It is biological.
Around ovulation, anandamide levels peak naturally. The enzyme responsible for breaking down anandamide hits its lowest point right at ovulation, allowing endocannabinoid concentrations to remain elevated (Brents, Yale Journal of Biology and Medicine, 2016). Adding exercise on top of this hormonal backdrop creates ideal conditions for a strong runner's high.
During the luteal phase, when progesterone dominates and estrogen falls, the picture shifts. CB1 receptor activity decreases, and the enzymes that degrade endocannabinoids become more active. Progesterone has mild antagonistic effects on cannabinoid receptors, which may explain why movement feels heavier and the euphoric payoff seems muted in the days before menstruation (Brents, Yale Journal of Biology and Medicine, 2016). This does not mean training during the luteal phase is without value: there are other metabolic advantages during this window. But it does explain why the same run that felt transcendent earlier in the cycle can feel like pushing through resistance a week later, and why your muscles might feel heavier and your system slower. That variability is not a failure. It is your endocannabinoid system responding to estrogen's rise and fall.
How training history changes what you feel
The 2024 Weiermair study found that regular runners tend to experience a more pronounced psychological lift from running, reporting stronger mood improvements than occasional runners. Interestingly, occasional runners show a more chemically pronounced spike in 2-AG, suggesting that for a newcomer the high is a more raw chemical surge, while for the experienced runner it becomes a more refined and sustained psychological shift (Weiermair et al., Sports, 2024).
There is also a homeostatic adaptation to be aware of. While a single run produces a spike in endocannabinoid activity, chronic overtraining can produce the opposite effect over time. If the system is repeatedly stimulated at high intensity, the body may increase the activity of the enzyme responsible for breaking down anandamide in order to restore balance. A 2023 systematic review found that while acute exercise reliably increases endocannabinoids, long-term high-volume endurance training programmes can lead to a decrease in baseline endocannabinoid levels (Siebers, Biedermann and Fuss, Neuroscientist, 2023).
Studies of exercise dependency have found that individuals with compulsive exercise patterns had lower baseline anandamide levels at all time points, and when deprived of exercise, experienced what amounts to a literal chemical withdrawal: fatigue, irritability, and confusion. The system that is supposed to reward movement had been downregulated by overuse. This is worth holding in mind, particularly for women who use training as their primary tool for managing stress and mood.
What this means in perimenopause
For women in perimenopause, where estrogen is declining in an erratic and non-linear pattern, the endocannabinoid equation shifts.
Inconsistent estrogen levels mean inconsistent endocannabinoid signalling, which can make runner's high less predictable (I have noticed this myself). The research on this interaction across the menopausal lifespan is still developing, but the bidirectional crosstalk between estrogen and the endocannabinoid system is well established (Meccariello et al., International Journal of Molecular Sciences, 2021). When estrogen fluctuates as it does in perimenopause, the system loses some of its rhythmic predictability. It does not disappear, but the experience of exercise shifts.
Some days the familiar wave arrives. Other days, despite doing everything right, it does not. Understanding the hormonal context behind that variability removes a significant amount of self-blame and allows you to approach movement as beneficial even when it does not feel blissful.
In my own experience, HRT has made runner's high more consistent, and the addition of testosterone has restored the drive to get the work done in the first place. That is my personal experience and it will be different for every woman and every phase she is in. Fuelling strategy also plays a role: a body that is under-resourced will not produce the same endocannabinoid response as one that is properly fuelled.
For women in perimenopause managing anxiety, disrupted sleep, or low-grade mood changes, consistent moderate-intensity movement is a genuine tool for nervous system regulation. The endocannabinoid system overlaps significantly with the hypothalamic-pituitary-adrenal axis, meaning that exercise-induced endocannabinoid release can help recalibrate stress responses over time (Matei et al., International Journal of Molecular Sciences, 2023). This is why exercise can feel, on the right day, genuinely better than anything else available to you. You are directly influencing the receptors that regulate fear extinction, emotional processing, and stress recovery.
For women whose cycles are no longer predictable, or who are postmenopausal, consistency matters more than intensity. Regular moderate exercise trains the endocannabinoid system to respond even when hormonal support is less reliable. The system evolved to reward movement. It responds well to being given the opportunity to do so.
References:
Brents, L.K. (2016) 'Marijuana, the endocannabinoid system and the female reproductive system', Yale Journal of Biology and Medicine, 89(2), pp. 175-191.
Craft, R.M. (2012) 'Sex differences in cannabinoid pharmacology: a reflection of differences in the endocannabinoid system?', Life Sciences, 92(8-9), pp. 476-481.
Matei, D., Trofin, D., Iordan, D.A., Onu, I., Condurache, I., Ionite, C. and Buculei, I. (2023) 'The endocannabinoid system and physical exercise', International Journal of Molecular Sciences, 24(3), 1989.
Meccariello, R., Santoro, A., D'Angelo, S., Morrone, R., Fasano, S., Viggiano, A. and Pierantoni, R. (2021) 'The complex interplay between endocannabinoid system and the estrogen system in central nervous system and periphery', International Journal of Molecular Sciences, 22(3), 972.
Montgomery, G.W., Tanaka, K., Subramaniam, S., Atluri, S., Amoako, A.A. and Mortlock, S. (2022) 'Gene expression of the endocannabinoid system in endometrium through menstrual cycle', Scientific Reports, 12, 9172.
Raichlen, D.A., Foster, A.D., Gerdeman, G.L., Seillier, A. and Giuffrida, A. (2012) 'Wired to run: exercise-induced endocannabinoid signaling in humans and cursorial mammals with implications for the "runner's high"', Journal of Experimental Biology, 215(8), pp. 1331-1336.
Siebers, M., Biedermann, S.V. and Fuss, J. (2023) 'Do endocannabinoids cause the runner's high? Evidence and open questions', Neuroscientist, 29(3), pp. 352-369.
Tanaka, K., Subramaniam, S., Atluri, S., Amoako, A.A., Mortlock, S., Montgomery, G.W. and McKinnon, B. (2024) 'Endometrial cell-type specific regulation of the endocannabinoid system and the impact of menstrual cycle and endometriosis', Cannabis and Cannabinoid Research, 10(4), pp. 512-526.
Weiermair, T., Svehlikova, E., Boulgaropoulos, B., Magnes, C. and Eberl, A. (2024) 'Investigating runner's high: changes in mood and endocannabinoid concentrations after a 60 min outdoor run considering sex, running frequency, and age', Sports, 12(9), 232.
If you're a woman in perimenopause struggling with metabolic health despite doing "all the right things," the missing piece might be understanding your unique internal landscape. My Sérenité Women's Wellness Program uses blood pathology analysis to create truly personalized nutrition protocols that work with your specific metabolism. Learn more about working together
