Nitrogen narcosis: what we (think we) know
Even in OWD—every beginner course—nitrogen narcosis is covered. The focus is usually on deeper dives; from around 30 m, nitrogen narcosis can become relevant. But people notice from the very first metres that something feels “different”. So there are changes that can’t yet be true nitrogen narcosis—but thinking, perception and action underwater are fundamentally different from on land.
Nitrogen narcosis—the more technical term for “depth intoxication”—is caused by high nitrogen partial pressures underwater. The deeper we dive on air, the higher the partial pressure of nitrogen we breathe. At some point, that nitrogen can have a narcotic effect on the nervous system.
So far, the textbook knowledge is fairly clear. It gets harder when you ask what divers actually mean when they say, “I was narced.” Because the term is used to lump together a whole range of things: mild impairment, a pleasant buzz, false confidence, fear, perceptual changes, slowing down—and in very rare reports even states where people were barely able to function for a moment.
So there isn’t just one kind of nitrogen narcosis. There are different manifestations that can overlap, sometimes gradually blending into each other and sometimes appearing surprisingly suddenly.
What is Nitrogen Narcosis?
One term for very different experiences
“Depth intoxication” sounds unsettling. The term “nitrogen narcosis”, used in the same sense, sounds almost medical—and for many, even more threatening. Anyone hearing about it for the first time usually has a lot of respect for it and waits for something very special to happen on the first deeper dives.
For some people, that’s exactly what happens. They suddenly feel unwell, get anxious, and want to go back up. Others relax, perhaps even become slightly euphoric. Many don’t notice anything at all, but conspicuously check their dive computer frequently. Others eventually pay attention to almost nothing at all. And it doesn’t start at the same depth for everyone.
When we talk about nitrogen narcosis, we can roughly mean three different things.
Not everything that feels different underwater is nitrogen narcosis
Underwater, we’re not simply the same people as on land—just with fins. Cold, work of breathing, distraction, equipment, stress, current, poor visibility, unfamiliar movements, and the simple fact that we—as land-dwelling creatures—are suddenly expected to function in an alien environment all change how we think and act. You can feel that in the first few metres.
You could say, somewhat pointedly: Underwater, everyone gets a bit dumber. Or expressed more scientifically: Underwater, even at shallow depths, it can be demonstrated that cognitive performance may be impaired—and that this effect can persist even after the dive. That’s not nitrogen narcosis in the narrow sense. But it explains why some things already feel more complicated underwater in shallow water than they do on land. And it’s important not to confuse this level with nitrogen narcosis.
In this project, we’re mainly interested in the effect nitrogen can have at greater depths under higher pressure. But the other factors don’t disappear—they add to it.
The pleasant narcosis
Nitrogen narcosis is often not threatening at all. Sometimes it’s rather pleasant: Everything feels a bit easier. Things that were annoying higher up suddenly don’t matter anymore. The depth feels calm, beautiful, special. You’re relaxed—maybe even a little euphoric. A bit “tipsy”, to compare it with more familiar intoxicated states. That’s probably where the term “martini effect”, common especially among older divers, mainly comes from.
This is precisely where one of the difficulties lies. Pleasant nitrogen narcosis doesn’t feel like a warning signal. It feels more like everything is just fine. Maybe everything is fine. Maybe you can still react sensibly, keep your buddy in sight, take gas management seriously, and control your own depth. Then this mild narcosis is something that many divers know and sometimes even enjoy. But pleasant doesn’t automatically mean safe.
If you’re very happy and content down there, don’t really want to surface, and yet you’ve just forgotten how much gas is left in the tank even though you checked a moment ago—then it’s no longer a poetic feeling of depth. It’s a sign that perception, attention and judgement have already changed.
When it tips over
An actually pleasant high can suddenly change. Whether, when and why this happens isn’t always clear.
That’s exactly one of the dangers: if you feel too secure in the pleasant, light euphoria, you may miss the right moment to ascend.
Calm can turn into uncertainty. Fascination can turn into fear. Colours may seem more intense; sounds strangely close or far away. Some report music, tones, singing, or an altered sense of time and space. The way up can suddenly seem very long. The environment can feel unfamiliar. You really want to go back up—now.
These descriptions sound dramatic, but they’re part of what some divers report from deep air dives—especially from times when trimix wasn’t yet available or was used far less widely.
Even more serious are reports of states sometimes described as “wah-wah”: everything roars, perception collapses, and afterwards you can barely remember how you made it back to the surface. The term was coined by Bob Raimo in a very personal account.
Very occasionally, there are also reports of a kind of “absence”: divers are not unconscious for a moment, but they’re also not really reachable or capable of acting. Such reports are rare, hard to classify, and not cleanly explained scientifically. But they do appear in accounts by experienced deep divers, including Sheck Exley.
For today’s recreational air dives to around 40 m, such severe loss of control isn’t the typical scenario. Much more relevant is the milder, harder-to-spot change: less attention, poorer judgement, more ease, less control.
How to recognize nitrogen narcosis
Nitrogen narcosis isn’t a neatly ordered symptom ladder. It’s not that concentration problems come first, then euphoria, then fear, then loss of control. Individual changes can appear suddenly, mix together, or be barely visible from the outside. Sometimes the affected person notices little themselves. Sometimes the buddy sees much earlier that something is off.
Still, there are patterns that are described again and again.
Attention and thinking
What seems self-evident on land can become complicated underwater. Simple tasks take longer. You forget things you just knew. You look at the computer and shortly afterwards can’t remember exactly what it said. You need more time to interpret information.
That’s probably closely linked to attention. Some studies on changes in cognitive performance underwater examined exactly this phenomenon: even comparatively small pressure-related changes can have measurable effects on attention and performance. The page on the current evidence goes into this in more detail.
Mood and judgement
Many reports of nitrogen narcosis don’t start with fear, but with a sense of wellbeing. Everything is beautiful. Everything is easy. The dive feels special. Limits seem less urgent. Things that actually need attention—gas, time, depth, buddy, plan—move a little further into the background.
That’s tricky because it doesn’t feel like loss of control. It feels more like control. From the outside, this behaviour is often perceived differently than it feels to the diver in that moment: someone with a clear head may notice a certain scatterbrainedness and carelessness.
Perception
Nitrogen narcosis can change perception. Colours may seem more intense, sounds unfamiliar, the environment unusually clear—or unusually unreal. Some describe an altered sense of time. Others later remember details they couldn’t really make sense of in the moment.
These reports are hard to measure, but they’re important for understanding. Because nitrogen narcosis isn’t just about reaction tests—it’s also a change in experience.
Ability to act
When attention, judgement and perception change, your ability to act suffers too. That doesn’t have to look dramatic right away. It can mean someone reacts more slowly, no longer actively follows the plan, loses sight of their buddy, or can’t complete a simple task cleanly. If a real problem occurs in this state, problem-solving ability can be significantly impaired.
If you feel like you want to stay down there forever, you need to go up.
Now. Immediately.
What is probably happening in the nervous system
We know quite a bit about how nitrogen narcosis can feel and what symptoms are associated with it. Less clear is exactly how it develops. Nitrogen narcosis is probably a problem of information transmission in the nervous system.
In our nervous system, electrical impulses play a major role. But it gets particularly interesting at the contact points between nerve cells, the so-called synapses. There, between two nerve cells, lies a tiny gap, the synaptic cleft. Information must be transmitted chemically here: One nerve cell releases messenger substances, called neurotransmitters. These bind to matching receptors on the next cell and trigger new signals there. When this system is disrupted, information no longer arrives quite the way it should.
A common explanation is that nitrogen under high pressure alters exactly this signal transmission—not like a switch that’s simply flipped, but more like a system that works less cleanly, more slowly, or differently.
Graphic: Illustration of a synapse. DataBase Center for Life Science (DBCLS), CC BY 4.0
Meyer–Overton: an important clue, but not a complete explanation
A classic explanation for the narcotic effect of gases is the Meyer–Overton correlation. From research on anesthetic gases, we know there is a relationship between fat solubility and narcotic effect. Gases that have a narcotic effect at lower pressures tend to be highly fat-soluble. This led to the Meyer–Overton hypothesis: the narcotic effect of a gas is related to its fat solubility.
At first, that sounds plausible. Nerve cells and their connections are surrounded by fatty structures. If a gas dissolves in these areas, it could alter those structures and thereby affect signal transmission.
Today, this explanation on its own is considered too simplistic. Fat solubility seems to be an important clue, but not the whole story. Today it’s assumed that additional mechanisms are involved: specific receptors, different neurotransmitters, complex changes in signal transmission. Sufficient solubility in fatty tissue may be a kind of prerequisite for a gas to have any narcotic effect at all. But it doesn’t, by itself, explain why and exactly how the anesthetic effect occurs.
For example, changes in the dopamine system have been demonstrated in animal experiments. Other research approaches try to trace more precisely how nitrogen and other gases act on receptors and neurotransmitters. Some of these ideas come from anesthesia research—and conversely, research into inert gas narcosis may also be of interest to medicine.
To this day, there is no truly clear, simple, unambiguous explanation.
What remains open?
So nitrogen narcosis isn’t a complete mystery. We know enough to take it seriously. We know that depth, gas partial pressure, environment, task, stress, cold, work of breathing, and individual differences can all play a role. We also know that narcosis doesn’t always feel the way you’d expect from textbook lists.
But we don’t know enough to explain every experience cleanly.
That’s exactly why we collect not only studies, but also reports: not to turn individual experiences into simple truths, but to take a closer look at which patterns repeat across these experiences.
