Several gases can cause hallucinations, but the most well-known is nitrous oxide, commonly called “laughing gas.” It produces euphoria, dissociation, and mild perceptual distortions when inhaled. Other gases, including volatile solvent vapors, carbon dioxide at high concentrations, carbon monoxide, and even the nitrogen in regular air under deep-water pressure, can also trigger hallucinations under the right conditions.
Nitrous Oxide (Laughing Gas)
Nitrous oxide is the gas most people encounter in a medical or dental setting, where it’s used as a mild sedative mixed with oxygen. It works by blocking a specific receptor in the brain that normally handles excitatory signaling, producing a rapid drop in stimulating brain activity. This is the same basic mechanism that ketamine uses, which explains why both substances create feelings of dissociation and altered perception. Nitrous oxide also activates opioid receptors and stimulates the brain’s reward pathway, which accounts for the intense euphoria users describe.
At controlled medical doses, nitrous oxide produces mild relaxation and slight perceptual changes. At higher concentrations or with repeated inhalation, the effects shift toward stronger dissociation, visual distortions, and hallucinations. People who misuse it recreationally typically inhale it from small pressurized canisters (sometimes called “whippets”), and heavy users may go through 75 to 100 canisters per day.
The serious risk with nitrous oxide isn’t the hallucinations themselves. It’s what the gas does to vitamin B12. Nitrous oxide chemically destroys the form of B12 your body needs for nerve function by oxidizing a key cobalt atom in the vitamin’s structure. Without functional B12, the insulation around your spinal cord and peripheral nerves begins to break down. Symptoms of this nerve damage can appear anywhere from a few days to six months after heavy use, or two to six weeks after even a single exposure in someone who already has low B12 levels.
Volatile Solvent Vapors
The fumes from common household and industrial products, including paint thinners, glues, gasoline, and certain aerosols, contain chemicals that can cause hallucinations. The most studied of these is toluene, a solvent found in paint, lacquer, and adhesives. Toluene has been classified as a “non-classical hallucinogen” because it activates the same serotonin receptors (5-HT2A) that classic psychedelic drugs like LSD target. It also blocks excitatory brain receptors in the same way nitrous oxide and ketamine do, creating a double mechanism for altering perception.
Toluene raises serotonin levels across multiple brain regions, including the frontal cortex, the memory center, and the brainstem. This flood of serotonin activity drives hallucinogen-like effects. Research in animals shows that toluene exposure during adolescence can permanently increase the sensitivity of serotonin receptors in the prefrontal cortex, the area responsible for decision-making and perception. This means young people who inhale solvents may become more vulnerable to psychosis long after they stop using them.
Deliberate inhalation of volatile solvents is widespread globally, particularly among adolescents and young people, largely because these products are legal and easy to obtain. Beyond hallucinations, solvent inhalation carries risks of sudden cardiac arrest, liver damage, and permanent brain injury.
Carbon Dioxide at High Levels
Carbon dioxide isn’t typically thought of as a hallucinogenic gas, but when it builds up in the blood beyond normal levels, it can cause hallucinations along with confusion, slurred speech, headache, and altered consciousness. This condition, called hypercapnia, occurs when blood CO2 levels rise above 45 mm Hg (the normal range sits between 35 and 45). It causes blood vessels in the brain to widen, increasing pressure inside the skull and disrupting normal brain function.
You wouldn’t normally encounter dangerous CO2 levels in everyday life. Hypercapnia typically happens in people with severe lung disease, during equipment failures in enclosed spaces like submarines or spacecraft, or in situations where someone is rebreathing their own exhaled air. The hallucinations from CO2 buildup are a sign of serious medical danger, not a recreational effect.
Carbon Monoxide
Carbon monoxide is an odorless, colorless gas produced by burning fuel, and it’s one of the most common causes of accidental poisoning. When inhaled, it binds to red blood cells roughly 200 times more tightly than oxygen does, starving the brain of oxygen. Neuropsychiatric effects, including hallucinations, confusion, and personality changes, occur in up to 50% of people who experience toxic exposure levels. These symptoms tend to appear when the percentage of carbon monoxide bound to hemoglobin in the blood reaches 25% to 50%, a range that also causes difficulty breathing and loss of consciousness.
What makes carbon monoxide particularly dangerous is that hallucinations and confusion can persist or reappear days to weeks after the initial exposure, even after the gas itself has cleared from the blood. This delayed neurological damage happens because oxygen deprivation triggers inflammation and cell death in vulnerable brain regions.
Nitrogen Under Pressure
Regular nitrogen, the gas that makes up 78% of the air you breathe, becomes a hallucinogen under the right conditions. Scuba divers who descend beyond about 30 meters (roughly 100 feet) while breathing normal air can experience nitrogen narcosis, sometimes called “rapture of the deep.” At that depth, the increased water pressure forces more nitrogen to dissolve into the blood, and it begins to affect the brain.
The first symptoms resemble mild alcohol intoxication: impaired judgment, poor concentration, and euphoria. As a diver goes deeper, the effects escalate to include idea fixation, loss of manual dexterity, hallucinations, and eventually stupor or coma. All divers are significantly impaired at 60 to 70 meters, though some individuals feel effects as shallow as 30 meters. The good news is that nitrogen narcosis reverses completely as the diver ascends and the excess nitrogen leaves the blood. The bad news is that impaired judgment at depth can prevent a diver from recognizing they need to ascend at all.
Anesthetic Gases in Medical Settings
Powerful anesthetic gases used during surgery, such as sevoflurane and desflurane, can cause hallucinations and agitation as they wear off. This is most common in children. In one study of pediatric patients undergoing ear, nose, and throat surgery, roughly 70% of children in both the sevoflurane and desflurane groups showed signs of emergence delirium, which can include confusion, hallucinations, and combative behavior. These episodes peak within the first 15 minutes after arriving in recovery and typically resolve within 30 minutes, though occasional cases last up to an hour.
Adults can also experience hallucinations during anesthesia recovery, though it’s less common. These episodes are temporary and don’t indicate any lasting neurological harm. They’re simply a side effect of the brain transitioning back to normal consciousness after being chemically suppressed.
Why These Gases Affect the Brain
Despite their chemical differences, hallucinogenic gases share a few common mechanisms. Most of them either block excitatory signaling in the brain (the same pathway ketamine disrupts), activate serotonin receptors involved in perception, or deprive the brain of oxygen. Some, like toluene, do more than one of these simultaneously. The hallucinations themselves arise because the brain, deprived of normal signaling patterns, begins generating its own sensory content to fill the gaps.
The intensity and character of the hallucinations depend on which gas is involved, how much is inhaled, and how long the exposure lasts. Nitrous oxide tends to produce dreamy, dissociative visual distortions. Solvent vapors can cause vivid, sometimes frightening hallucinations. Carbon monoxide and carbon dioxide hallucinations are typically accompanied by confusion so severe that the person may not realize they’re hallucinating at all, which is part of what makes those exposures so dangerous.