This Is Your Brain…This Is Your Brain on Less Oxygen: Any Questions?*

For years, I’ve been suggesting that some of the extraordinary experiences produced by intense breathwork might have a very non-mystical, physiological explanation: the brain may be receiving less oxygen, not more.

I’m talking about practices such as Holotropic Breathwork, Rebirthing, Conscious Connected Breathing, and the rapid-breathing phases of the Wim Hof Method. These techniques can produce powerful sensations, emotional experiences, changes in perception, and sometimes states that participants describe as mystical or transcendent.

As with my recent articles about why we really don’t want to breathe like babies, a closer look at respiratory physiology reveals a much different story than you might hear from a proponent of any of the above methods.

More breathing doesn’t necessarily mean more oxygen

Most people assume that taking lots of deep, rapid breaths increases the amount of oxygen reaching the brain. It sounds reasonable, but that’s not how our respiratory system actually works.

Under ordinary conditions, the hemoglobin in our arterial blood is already carrying nearly as much oxygen as it can. Breathing harder generally doesn’t add much more. What it does do is remove more carbon dioxide (CO₂).

Carbon dioxide isn’t merely a waste product. It plays an essential role in regulating how oxygen reaches our tissues.

When we hyperventilate, CO₂ levels can drop dramatically and rapidly. This produces two important effects: blood vessels in the brain constrict, reducing blood flow, and changes in blood chemistry make hemoglobin hold onto oxygen more tightly, making it less inclined to release into the tissues. This second phenomenon is known as the Bohr effect.

So here’s the paradox: you can be breathing vigorously, have plenty of oxygen in your blood, yet still be reducing the amount of oxygen available to your brain.

What does the research show?

A 2025 study published in Communications Psychology investigated 61 experienced practitioners of Holotropic and Conscious Connected Breathwork. Researchers measured carbon dioxide levels during sessions and compared them with participants’ reports of altered consciousness.

They found that falling CO₂ levels were significantly associated with the onset of altered states. The more participants depleted their CO₂, the more likely they were to report changes in consciousness.

A 2026 brain-imaging study went further. Researchers examined 30 experienced practitioners of high-ventilation breathwork, using MRI to measure blood flow through the brain before and during the exercises.

The study found that high-ventilation breathwork produced an average reduction in blood flow through the brain’s gray matter of 45.5%.

That’s an astounding finding. It doesn’t mean the brain received exactly 45.5% less oxygen, nor does it definitively establish that participants experienced brain tissue hypoxia. What it did demonstrate was a substantial reduction in the circulation supplying the brain during a practice designed to produce altered consciousness.

Interestingly, the degree of reduced blood flow didn’t reliably predict the intensity of the participants’ experiences, suggesting that other factors are also involved.

What do fighter pilots have to do with this?

For decades, military researchers have studied what happens to fighter pilots and astronauts when they undergo centrifuge training that exposes them to powerful gravitational forces.

Under high G-forces, blood is pulled away from the head, reducing circulation to the eyes and brain. Subjects may experience tunnel vision, visual darkening, disorientation, dreamlike sensations, and eventual loss of consciousness.

Some have also reported experiences resembling aspects of what are commonly called near-death experiences.

Aerospace physician James Whinnery investigated hundreds of these episodes and published a fascinating comparison in 1997: Psychophysiologic Correlates of Unconsciousness and Near-Death Experiences.

One particularly striking feature is tunnel vision: the visual field narrows as the periphery darkens, sometimes leaving a small central area of light before vision disappears. Some near-death accounts include the more elaborate sensation of traveling through darkness toward a brilliant light.  Participants in many breathwork trainings are led to believe this exact same phenomenon is a re-experiencing of their journey through the long dark tunnel of their mothers' birth canal, thus the association with "re-birthing."

In centrifuge training, the problem is reduced blood pressure at brain level. In hyperventilative breathwork, it’s primarily the loss of CO₂ that constricts cerebral blood vessels. Different causes, but potentially overlapping consequences for the brain.

These aren’t necessarily identical phenomena, but the similarities are hard to ignore..

And then there’s Wim Hof

The Wim Hof Method adds another dimension because it combines repeated rapid breathing with periods of breath retention.

The rapid breathing lowers CO₂. During the subsequent breath holds, blood oxygen levels can fall dramatically.

In a 2014 study published in Proceedings of the National Academy of Sciences, researchers documented how Wim Hof method produced pronounced respiratory alkalosis and, during some breath holds, severe reductions in oxygen saturation among participants trained in the method.

The study also demonstrated changes in adrenaline and inflammatory responses. But showing that a technique can dramatically alter physiology isn’t the same as establishing that those alterations are beneficial.

And, because the Wim Hof method if often practiced in water, with submerged breath holding, it can be incredibly dangerous. Scott Carney, a former advocate of Wim Hof, investigated 21 deaths and 18 injuries associated with the practice.

Live Science, in 2024, published Gambling With Your Life: Experts Weigh In on Dangers of the Wim Hof Method.  Their independent examination of the physiological risks found hypoxic blackouts and drowning following hyperventilation, potentially dangerous cardiac arrhythmias, and contradictions between official safety warnings and Hof’s public demonstrations.

Extraordinary experiences, ordinary physiology?

Someone might have a profound emotional experience during breathwork, gain a new perspective on a personal problem, or feel considerably better afterward. None of that needs to be dismissed, but we should distinguish those experiences from the explanations being offered to explain them.

If someone experiences a sense of leaving their body, that doesn’t establish that consciousness has literally separated from the body. If someone experiences an overwhelming emotional release, that doesn’t establish that stored trauma has been expelled from their tissues.

And if someone feels they’ve accessed a higher level of consciousness, we should at least consider whether they’ve experienced an altered state partly produced by reduced cerebral circulation.

A powerful experience isn’t necessarily evidence that the story we tell about it is true.

There’s also a practical safety issue. Hyperventilation and breath retention can cause fainting, and lowering CO₂ can suppress the urge to breathe even as oxygen levels fall. These practices should never be combined with swimming or bathing. People with cardiovascular, neurological or respiratory conditions have additional reasons for caution.

What if the real benefit of breathwork is something much simpler?

In my recent articles about infant breathing, I challenged the popular idea that adults should imitate babies because infants supposedly possess a naturally correct breathing pattern.

Babies breathe the way they do because they have very different respiratory mechanics and metabolic demands. Their breathing is appropriate for their circumstances, not a model of ideal adult respiration.

I think something similar gets overlooked in discussions of breathwork.

We spend enormous amounts of time debating which breathing technique is best, which pattern activates the right part of the nervous system, or which practice supposedly unlocks some extraordinary physiological or psychological benefit.

But what if the most valuable long-term benefit of learning a new breathing technique is simply that in learning a new way to breathe, we’re necessarily unlearning our habitual way of breathing?

Our breathing patterns develop over a lifetime in response to our bodies, experiences, activities and environments. Some of those patterns become so familiar that we scarcely notice them, let alone recognize that we have alternatives.

Learning to breathe differently gives us those alternatives. It allows us to experience how our respiratory system responds to changes in rhythm, depth, effort, posture and attention. Perhaps we discover that the pattern we’ve been using isn’t the only one available to us.

And that’s where I think the real value lies: not in replacing one supposedly incorrect breathing pattern with a new, supposedly correct one, but in expanding our capacity to adapt.

That kind of freedom doesn’t require mystical explanations, extraordinary experiences, or deliberately compromising the circulation supplying our brains. It requires something both simpler and more challenging: learning how to do something differently, and discovering that we have a choice.

* For readers who weren’t around in the 1980s, the title and illustration for this article are a nod to the famous 1987 anti-drug public service announcement, “This Is Your Brain on Drugs.”⁠  It featured an egg, a frying pan, and the unforgettable closing line: “Any questions?”

Research referenced

• Decreased CO₂ saturation during circular breathwork supports emergence of altered states of consciousness. Communications Psychology (2025).
• How high ventilation breathwork alters consciousness: Hypoperfusion, network dynamics, and subjective experience. (2026).
• Whinnery, J. E. (1997). Psychophysiologic correlates of unconsciousness and near-death experiences. Journal of Near-Death Studies, 15(4), 231–258.
• Kox, M., et al. (2014). Voluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humans. Proceedings of the National Academy of Sciences, 111(20), 7379–7384.

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