Forget Endorphins: The Real Science Behind Runner's High and Why Women Feel It More Intensely.
After experiencing the elusive runner's high on almost all my runs, regardless of distance or duration, I wanted to understand exactly what was happening inside my body. It felt almost criminal that I could feel so invincible after exercising
That post-run "glow" is the holy grail of the endurance world, a shimmering state of euphoria, reduced pain, and tranquility that makes those early morning km’s worth the effort. For decades, we've been told this magic is the work of endorphins. It's a tidy, comforting story, but according to the latest neurobiological research, it's almost certainly a myth.
Despite its fame, the runner's high remains surprisingly elusive. Research indicates that only 69% to 77% of runners have ever actually experienced it. If you've ever wondered why that "glow" sometimes feels like a no-show, the answer lies within a much more complex internal pharmacy-our own "cannabis-like" endocannabinoid system.
The heavy hitters of this internal pharmacy aren't endorphins at all. Recent evidence suggests that while we've been praising opioids, our bodies have been rewarding us with a natural, exercise-induced "stone" that's far more sophisticated than we imagined.
The Endorphin Myth vs. The Lipophilic Reality
The media has clung to the "endorphin hypothesis" since the 1980s, but scientific support for it is remarkably thin. The primary hurdle is a biological gatekeeper known as the blood-brain barrier (BBB). This selective membrane acts like a sophisticated filter, blocking large, water-soluble molecules like endorphins from entering brain tissue while allowing smaller, fat-soluble compounds to pass through freely.
In contrast, endocannabinoids are lipophilic (fat-loving) molecules. Their chemical structure allows them to slip through the blood-brain barrier easily, reaching the brain regions responsible for mood, reward, and pain perception. Because peripheral endorphins in the blood can't reach the regions responsible for emotional shifts, they're poor candidates for the runner's high. As researchers confirmed in a 2023 systematic review analyzing human studies: "The endorphin hypothesis was poorly supported by evidence, although it was widely perpetrated by the media" (Siebers, Biedermann & Fuss, 2023).
A 2023 study examining the complete literature on exercise and endocannabinoids found that when researchers blocked opioid receptors in human subjects, the euphoric effects of running remained unchanged. The endocannabinoid system was driving the experience all along (Matei et al., 2023).
The Body's Natural "Bliss Molecules"
Our internal pharmacy relies on two primary ligands: Anandamide (AEA) and 2-Arachidonoylglycerol (2-AG). These molecules bind to CB1 and CB2 receptors throughout the body. If those names sound familiar, it's because AEA binds to the same CB1 receptors as THC, the active compound in cannabis.
The name Anandamide is derived from the Sanskrit word ananda, meaning "bliss"—and for good reason. While 2-AG levels can be variable, research consistently shows a robust spike in Anandamide following exercise. By penetrating the brain and modulating reward and anxiety pathways, these molecules provide the biological foundation for the sedation and joy we associate with the high. In essence, your long run is a way to get "naturally stoned." Although that is certainly not why I do it!
Unlike endorphins, endocannabinoids are small, fat-soluble molecules that move easily across the blood-brain barrier. Once there, they interact with CB1 receptors concentrated in areas of the brain that regulate mood, memory, pain perception, and reward (Matei et al., 2023).
The effects go beyond just feeling good. Research shows that endocannabinoid release during exercise contributes to significant reduction in anxiety and stress reactivity, increased pain tolerance, improved emotional resilience that persists after the workout ends, and enhanced focus and working memory in the hours following exercise. I personally feel like my bones are made of rubber and air and I am the happiest version of myself.
The "Goldilocks Zone" Why Your Intensity Matters
Tapping into this bliss isn't just about hammering it. To trigger the release of these molecules, you have to hit the Goldilocks Zone—an intensity that's not too easy, but not too taxing. A 2023 systematic review analyzing 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 (AAMHR)—sustained for at least 20 to 30 minutes (Siebers, Biedermann & Fuss, 2023). Mine hits around the 20 minute mark.
You can find your target zone with a bit of simple math: subtract your age from 220, then multiply by 0.70. If you're just walking (below 50% AAMHR) or sprinting at a breathless 90% capacity, the body often fails to trigger the Anandamide release. The system demands a moderate, sustained effort to unlock the vault.
This is the zone where you're working hard enough to breathe deeply but can still maintain the effort without stopping. Walking at a brisk pace, steady cycling, or rhythmic running all fit this profile. High-intensity interval training produces different hormonal responses—beneficial in their own ways, but not particularly effective for endocannabinoid release. This is can confirm personally and it has been my experience.
Duration matters more than intensity. The system doesn't respond well to short bursts. You need time—at least 20 to 30 minutes of sustained movement before endocannabinoid levels begin to climb meaningfully. This is why brief, intense sessions might leave you feeling accomplished but not particularly blissful.
The Female Advantage & Why Women Experience Stronger Endocannabinoid Responses
The research gets fascinating for women specifically. A 2024 study tracking endocannabinoid levels after a 60-minute outdoor run found something striking, women showed significantly higher increases in anandamide concentrations compared to men following the same exercise protocol (Weiermair et al., 2024).
Both sexes experienced increased mood and elevated endocannabinoids post-run, but the magnitude of anandamide elevation—the primary molecule responsible for the euphoric feeling—was notably greater in female participants. The researchers measured plasma concentrations before and after running and found that while both endocannabinoids (AEA and 2-AG) increased in women, the AEA response was sex-specific, with females demonstrating a more pronounced rise. Love that for us…
This isn't an isolated finding. The endocannabinoid system shows clear sexual dimorphism, meaning it functions differently in male and female bodies. Research demonstrates that women are generally more sensitive to cannabinoid signaling—both from endogenous molecules produced during exercise and from external cannabinoids (Craft, 2012).
So why and how does this happen? Estrogen appears to be the key player. Estrogen enhances endocannabinoid signaling by multiple mechanisms: it increases the density of CB1 receptors in the brain, modulates the enzymes that synthesize and break down endocannabinoids, and influences how readily these molecules bind to their receptors (Brents, 2016).
The Menstrual Cycle Connection - When Exercise Feels Easy
Endocannabinoid system activity doesn't stay constant across the menstrual cycle. Research examining endometrial tissue has revealed that genes controlling endocannabinoid synthesis, degradation, and receptor expression fluctuate predictably with hormonal changes (Tanaka et al., 2024; Montgomery et al., 2022).
During the follicular phase (from menstruation through ovulation), when estrogen rises steadily, several things happen:
CB1 receptor expression increases in multiple tissues
Enzymes that synthesize anandamide become more active
Enzymes that break down anandamide (like FAAH) decrease
The net effect? Higher circulating endocannabinoid levels and greater receptor sensitivity. This is when many women report that workouts feel easier, recovery is faster, and the post-exercise mood boost is more pronounced. It's not just psychological, t's also biological.
Around ovulation, anandamide levels peak naturally. The enzyme that breaks down anandamide (FAAH) hits its lowest point right at ovulation, allowing endocannabinoid concentrations to remain elevated (Brents, 2016). Adding exercise on top of this hormonal backdrop creates ideal conditions for a robust runner's high.
During the luteal phase, when progesterone dominates and estrogen drops, the picture changes. 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, 2016).
This doesn't mean you should skip training during the luteal phase, necessarily as there are other metabolic advantages during this window—but it does explain why some weeks, the same run that felt transcendent earlier in the cycle now feels like pushing through resistance and why your muscles might feel heavier and your system feels slower.
How Often You Run Changes What You Feel
How you experience this high depends heavily on your habits. The 2024 study by Weiermair and colleagues found that regular runners tend to experience a more profound psychological lift, reporting stronger mood improvements than occasional runners.
However, there's an adaption response in that, while regulars get the better mood, occasional runners actually show a more raw, pronounced chemical spike in 2-AG. This suggests that for a newcomer, the "high" is a blunt chemical surge, whereas for the veteran, it becomes a more refined psychological shift (Weiermair et al., 2024).
The "Withdrawal" Factor and Homeostatic Downregulation
While a single run provides a spike in bliss, chronic over-training can lead to a counter-intuitive crash. This is governed by homeostatic downregulation. If you spike the system too often, the body tries to find a new balance by increasing the activity of FAAH, the enzyme responsible for breaking down Anandamide.
A 2023 systematic review examining chronic exercise found that while acute exercise increases endocannabinoids, long-term endurance training programs can lead to a decrease in baseline endocannabinoid levels. The neurobiological consequences of this downregulation aren't yet fully clear (Siebers, Biedermann & Fuss, 2023).
Studies of exercise addiction reveal that "addicted" individuals actually had lower baseline AEA levels at all time points. When deprived of exercise, these individuals experienced a literal chemical withdrawal which included fatigue, anger, and confusion—because their bodies had downregulated their natural bliss molecules to cope with the constant training.
This can lead to a dysfunctional system where the very thing that's supposed to make you feel good stops working the way it should.
What This Means for Perimenopause
For women in perimenopause or postmenopause, estrogen volatility or decline changes the endocannabinoid equation. Inconsistent estrogen levels mean inconsistent endocannabinoid signaling, which can make the runner's high less predictable.
Research on the endocannabinoid system across the lifespan is still emerging, but we know that the crosstalk between estrogen and endocannabinoid signaling is bidirectional (Meccariello et al., 2021). When estrogen fluctuates wildly—as it does in perimenopause—the endocannabinoid system loses some of its rhythmic predictability but it doesn’t mean it’s gone completely.
This doesn't mean the benefits disappear, but it does mean the subjective experience of exercise may shift. Some days you'll catch that familiar wave of euphoria. Other days, despite doing everything right, it won't arrive. Understanding this hormonal context removes the self-blame and allows you to view exercise as beneficial even when it doesn't feel blissful. Of course if you add HRT to the mix this could significantly increase the likelihood of you continuing to experience it but it may be less predictable. In my case, it has helped me get my runners high back, while the testosterone gave me the drive back to get the work done. This is my personal experience of course and it will be different for each woman and each phase she is in. Your fueling strategy will also contribute of course.
A New Recipe for Bliss
For women managing perimenopausal anxiety, chronic stress, or low-grade depression, consistent moderate-intensity movement becomes a tool for nervous system regulation. The endocannabinoid system overlaps significantly with the hypothalamic-pituitary-adrenal (HPA) axis, meaning that exercise-induced endocannabinoid release can help recalibrate stress responses over time (Matei et al., 2023).
This is why people describe exercise as better than therapy on good days. You're directly influencing the same receptors that regulate fear extinction, emotional processing, and stress recovery. The effect is real, measurable, and reproducible.
By hitting that 70-85% AAMHR for 30 to 45 minutes, you aren't just doing "cardio"—you're engaging a 1000’s of-years-old reward system designed to make movement feel like a miracle. Track how this feels across your cycle if you're still menstruating. You might notice that the same workout protocol feels wildly different depending on where you are hormonally. There's no moral failure in that variability—it's your endocannabinoid system responding to estrogen's rise and fall.
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 inconsistent.
If our bodies evolved to reward us for movement with a chemically induced high, what are the long-term biological costs of our modern, sedentary lifestyle? Perhaps the "high" isn't an optional perk, but a state of being we were never meant to live without.
Runners High for women
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.
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