Nitrous Oxide and Vitamin B12 Nerve Damage

Table of Contents

1. What Nitrous Oxide Is and Where It Is Used
2. How the Gas Switches Off Vitamin B12
3. Why a Normal B12 Blood Test Can Mislead
4. Who the Reports Describe
5. Symptoms Described in Case Series
6. How Hospitals Diagnose It
7. Treatment and Recovery in the Studies
8. How Fast Reported Cases Have Grown
9. Blood Clots, Deaths and Other Harms
10. Signs Hospitals Treat as Urgent
11. What Is Still Not Known
12. Key Research Papers
13. Connections
14. Featured Videos

What Nitrous Oxide Is and Where It Is Used

Nitrous oxide is a colourless gas made of two nitrogen atoms and one oxygen atom. It has three very different lives.

• Medicine. It has a long history as an anaesthetic gas, often called "laughing gas", used in dentistry, in childbirth and alongside other anaesthetics in surgery. Here the dose and the time are controlled, and the gas is mixed with oxygen.
• Food. It is the propellant in whipped-cream dispensers and the small chargers that fit them. It is used because it dissolves well in fat and makes cream foam.
• Recreation. The same chargers, and newer large, sometimes flavoured tanks, are emptied into balloons and inhaled for a brief feeling of euphoria and light-headedness. A 2026 review in Current Medical Research and Opinion describes the gas as now sold with easy and discreet access in forms that appeal to children and young adults, and estimates that more than 13 million people in the United States have used it recreationally at least once.

The nerve damage described on this page is overwhelmingly a story of the third use. Medical exposure is short and supervised; the reported anaesthetic cases describe people who were already low in vitamin B12 without knowing it (see Who the Reports Describe).

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How the Gas Switches Off Vitamin B12

Vitamin B12 is built around a single atom of cobalt. For B12 to do its work, that cobalt has to sit in a particular reduced chemical state. A 1993 paper in Archives of Surgery describes the core problem: nitrous oxide irreversibly oxidises the cobalt, and the oxidised B12 is inactive.

Inactive B12 matters because the body uses it in two enzyme reactions, both described in that paper and in a 2022 review of toxicity mechanisms in Food and Chemical Toxicology:

1. Methionine synthase uses B12 to turn homocysteine into methionine. Methionine feeds the body's "methylation" chemistry, which among many jobs maintains myelin, the fatty insulating sheath around nerve fibres. The review states that nitrous oxide inactivates this enzyme directly.
2. Methylmalonyl-CoA mutase uses a second form of B12 to process certain fats and amino acids. The review describes this enzyme as cofactor-depleted after nitrous oxide.

When the first enzyme stops, homocysteine builds up in the blood. When the second stops, methylmalonic acid builds up. Those two substances are therefore the tell-tale footprints of B12 that is present but not working. The review lists further affected pathways (the folate cycle, glutathione production, the cell's energy cycle), which is why so many different laboratory markers can shift.

Exactly how the chemical block leads to damaged myelin is not fully settled. A French study of 93 people who regularly used nitrous oxide found that lower blood methionine went along with more severe nerve symptoms, but the average methionine level in every severity group stayed within the normal range. The authors concluded that a fall in methionine cannot be the only mechanism, and that other mechanisms are probably involved.

The B12 absorption animation shows how B12 normally reaches the body; nitrous oxide works after that point, on B12 that has already been absorbed.

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Why a Normal B12 Blood Test Can Mislead

A standard B12 blood test counts how much B12 is in the blood. It cannot tell whether that B12 still has working cobalt. This produces the single most important feature of nitrous oxide nerve damage: the B12 number is often normal or only slightly low.

• The 2016 systematic review of the case literature in the American Journal on Addictions found low or low-normal B12 in 52 of its 91 cases, with homocysteine and methylmalonic acid "occasionally" raised.
• A Chinese study comparing 50 young people with nitrous oxide-related spinal cord damage against 48 older people whose damage had other causes found a median B12 of 218 pg/mL in the nitrous oxide group against 96 pg/mL in the other group, while homocysteine was raised to a similar degree in both.
• In a 21-patient Chinese series, homocysteine was clearly raised in 14 of 18 people tested, but B12 was low in only 3 of 18.
• In a 2026 study of adolescents aged 14 to 18 (5 new patients plus 54 from the published literature), B12 deficiency was found in 45%, but raised homocysteine or methylmalonic acid in 92%. The authors note that the damage can appear without anaemia.
• A 2026 study of 81 people across 100 hospital stays in six Sydney hospitals measured how well each test picked up spinal cord damage. Low B12 caught only 22% of cases and low holotranscobalamin (the "active B12" test) only 5%. Raised homocysteine caught 95% and raised methylmalonic acid 93%, though both were also raised in many people without spinal cord damage (specificity 13% and 45%).

The French hospital series reported the same picture from the other side: of 31 patients admitted for nitrous oxide use, the median homocysteine was 87.7 µmol/L (normal below 15) and the median methylmalonic acid 3.8 µmol/L (normal below 0.5), while folate stayed within the normal range. The authors called a functional B12 deficiency "a consistent feature". The broader role of methylmalonic acid as a B12 marker is covered on the Nerve Health and Neuropathy page.

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Who the Reports Describe

Recreational users, mostly young

Almost every recent series describes young adults. The average age was 22.6 years in the 21-patient Chinese series and in a seven-patient Thai series (ages 19 to 32); 21.4 years in the 50-patient Chinese comparison; and a median of 23.7 years in the French series, where 79% were men. The United States poison-centre data from 2003 to 2024 found that people aged 20 to 29 made up the largest share of calls (37%), and 63% were male. The 2026 adolescent study shows that teenagers as young as 14 are affected too.

The amount matters

The Sydney study estimated each person's weekly and total lifetime exposure. Higher cumulative exposure went along with worse nerve damage, including spinal cord degeneration and nerve damage in the limbs, and with more severe neuropathy. The authors describe total exposure as the strongest predictor of severe outcomes, a dose-dependent relationship. The adolescent study adds that a B12 level that was already marginal before use may be a predisposing factor, and calls this an open research question.

Anaesthesia in people already low in B12

Medical nitrous oxide causes this damage only rarely. The 1993 Archives of Surgery paper collected five cases (four from earlier literature and one new) in which people not known to be B12 deficient developed subacute combined degeneration of the spinal cord after nitrous oxide anaesthesia. The authors describe people with B12 deficiency as exceedingly sensitive to neurological deterioration after nitrous oxide anaesthesia, and report that if the problem goes unrecognised the deterioration can become irreversible and fatal. In these reports the gas did not create the deficiency from nothing; it tipped an existing, hidden deficiency over the edge. Common hidden causes of low B12, such as pernicious anaemia, long-term metformin or acid-suppressing medicines, and plant-only diets, are listed on the Vitamin B12 Deficiency hub.

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Symptoms Described in Case Series

The pattern described across the reports is damage to two places at once: the long nerves of the arms and legs, and the back and side columns of the spinal cord that carry position sense and movement signals. Doctors call the combination myeloneuropathy.

• Numbness and tingling that starts in the feet and hands. In the adolescent study, symptoms were predominantly sensory. In the 21-patient series, 62% reported a subjective loss of feeling.
• Unsteady walking and poor balance. Losing position sense means the feet no longer "report" where they are. In the 21-patient series, 71% had impaired vibration sense and a positive Romberg test (swaying or falling when standing with the eyes closed). Limb numbness, weakness and unsteady gait were the most common findings in both groups of the 50-versus-48 Chinese comparison.
• Weakness. Movement problems appeared in 19 of 21 patients in one series, and in about half of those the weakness was limited to both legs. Reflexes were reduced or absent in 67%.
• Bladder and sexual problems. The 2026 review lists bladder and erectile dysfunction and, less commonly, paralysis.
• Mind and mood. The 2016 systematic review found psychiatric effects, including psychosis, in 11 of its 91 cases. In the Thai series, two of seven patients had encephalopathy (confusion from brain dysfunction). The 2026 review lists cognitive problems, and the United States poison-centre data recorded confusion in 14% of calls.

The onset is typically subacute, meaning over days to weeks rather than minutes. In the Thai series, people had been inhaling the gas for between one month and one year before symptoms began. The 50-versus-48 comparison found that, at presentation, the nitrous oxide group had on average milder disability than older people with spinal cord damage from other causes.

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How Hospitals Diagnose It

The case series describe three pieces of evidence used together, along with the history of exposure, which the Sydney authors describe as central because the blood markers alone are not confirmatory.

Blood tests

Homocysteine and methylmalonic acid are the sensitive markers, for the reasons in the section above. The Sydney study measured a median homocysteine of 50 µmol/L (normal 5 to 15) with a half-life of about 14.6 hours, and a median methylmalonic acid of 0.68 µmol/L (normal below 0.27). The 2026 review reports that guidance from the European Federation of Clinical Chemistry and Laboratory Medicine sets out the diagnostic parameters.

The "inverted V" on spinal MRI

Magnetic resonance imaging (MRI) of the neck part of the spine can show a bright signal in the back columns of the cord. On a cross-section image, the two damaged columns side by side form a shape like an upside-down letter V, which radiologists call the "inverted V" sign. In the 50-patient Chinese comparison, MRI was abnormal in 80% of the nitrous oxide group and the inverted V sign appeared in 72%, against 31.2% of people with spinal cord damage from other causes. The nitrous oxide lesions were wider but covered fewer spinal segments. In the 21-patient series the sign appeared in 8 of 17 scans, and in the adolescent study MRI showed long changes in the back columns in 89%. A normal MRI does not rule the condition out: in the Thai series, only two of seven patients had a visible lesion.

Nerve conduction tests

Electrical tests of the limb nerves typically show an axonal pattern, meaning the nerve fibres themselves are damaged, not only their insulation. This was found in 17 of 20 patients in the 21-patient series, in 88% in the adolescent study, and in all seven Thai patients.

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Treatment and Recovery in the Studies

The treatment described in the case series has two parts: the exposure to the gas ends, and vitamin B12 is replaced. The 2026 review reports that the European laboratory-medicine guidance describes supportive care and replenishing B12 with intramuscular cyanocobalamin (B12 injections). The same review reports two unsettled points: adding methionine directly "may" have a role but is not universally recommended, and routine folic acid is controversial, with the authors favouring it only when blood folate is low.

What happened afterwards

• Adolescents (59 patients). With B12 treatment, 27% recovered and 61% improved, which leaves about one in eight with no recorded improvement.
• 21-patient Chinese series (6 to 12 months of follow-up). B12, homocysteine and MRI findings recovered rapidly after B12 replacement, and the authors called the outlook "relatively good".
• Thai series (7 patients). At about two months, every patient had only minimal improvement. After more than six months, most had moderate to complete recovery. The authors describe the short-term outcome as generally unfavourable and the long-term outcome as showing remarkable improvement.
• Rehabilitation cohort (16 patients, Sydney, 2015 to 2022). Patients aged 18 to 43 were referred for rehabilitation, and every one needed help to walk or with self-care on admission. Their independence scores rose from a median of 84 to 117 with inpatient rehabilitation, but all of them still needed further rehabilitation after discharge.

Read together, the studies describe recovery that is often good but slow and not always complete, and the Sydney study links the most severe damage to the largest total exposure. The general B12 recovery timeline is discussed on the Nerve Health and Neuropathy page.

The United States poison-centre analysis found that B12 or folate treatment was recorded in only 6.3% of calls. The authors read this, together with the high number of single-substance exposures, as a sign that both the diagnosis and its severity are under-recognised.

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How Fast Reported Cases Have Grown

• United States. A 22-year analysis of the National Poison Data System found 1,751 calls about intentional nitrous oxide misuse in people aged 13 and over from 2003 to 2024. Yearly calls rose from 28 in 2003 to 401 in 2024, an increase of 1,332%. Over half (55%) of exposures had moderate or major effects, including numbness (12%), unsteady movement (11%) and confusion (14%); 29% led to hospital admission and 10% to intensive care. Most exposures (85%) happened at home. The authors suggest that newer flavoured, high-volume tanks may be contributing. The 2026 review adds that deaths rose six-fold from 2010 to 2023.
• Australia. Calls about nitrous oxide to Australian Poisons Information Centres rose sixfold, from 16 in 2016 to 111 in 2020. Among yearly samples of people who regularly use ecstasy or other stimulants, recent nitrous oxide use rose by about 10% a year from 2009 to 2020, with the sharpest rise from 2015 to 2018. Frequency and amount per user stayed stable and low in that group, and use and online interest had levelled off in recent years, while harms kept rising.
• France and Australia, hospital level. The French series recorded 31 admissions in 34 months at a single university hospital and called nitrous oxide use an emerging public health problem in France. The Sydney rehabilitation audit described referrals rising over its eight years.

On regulation, the papers read for this page do not describe specific laws. The United States poison-centre authors call for better clinical awareness, regulatory oversight and public health measures, and the 2026 review names public health information and regulation as ways to prevent harm.

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Blood Clots, Deaths and Other Harms

Nerve damage is the best-known harm, but not the only one.

• Blood clots. A 2022 systematic review found 14 patients in 13 published reports with clots linked to recreational nitrous oxide: deep vein thrombosis, pulmonary embolism, clots in the gut, liver and spleen veins, clots in the brain's veins, stroke, heart attack and clots in limb arteries. The authors suggest the high homocysteine produced by inactivated B12 as a possible link, while noting that the exact mechanism is unclear. They describe ending the inhalation as necessary to prevent recurrent clots.
• Deaths. The 2016 systematic review found 11 publications reporting 29 deaths related to nitrous oxide misuse.
• Acute injuries. The 2016 review lists pneumomediastinum (air leaking into the chest) and frostbite from the very cold gas; the 2026 review lists frostbite and asphyxia (lack of oxygen).
• Blood. The 2026 review lists macrocytic anaemia (large, immature red cells), the same blood picture seen in other forms of B12 deficiency.
• Raised pressure inside the skull. Two of the five new adolescent patients had raised intracranial pressure, which the authors suggest as a possible association needing further study.

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Signs Hospitals Treat as Urgent

The reports above describe damage that can progress and that, in the anaesthetic cases, became irreversible when it went unrecognised. Hospitals treat these signs in someone exposed to nitrous oxide as urgent:

• numbness or tingling that is spreading up the legs or into the hands over days
• new difficulty walking, frequent falls, or legs that "do not know where they are", especially in the dark
• new weakness of the legs or arms
• loss of bladder or bowel control
• confusion, hallucinations or a sudden change in behaviour
• signs of a clot: a swollen, painful leg; sudden chest pain or breathlessness; sudden weakness of one side of the face or body, or difficulty speaking

The general B12 red-flag list is on the Vitamin B12 Deficiency hub. Decisions about testing and treatment belong with a clinician.

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What Is Still Not Known

• A safe amount. The Sydney study found a dose-dependent relationship, but no study read for this page sets a threshold below which recreational use is free of nerve risk. Exposure amounts in these studies are self-reported estimates.
• Why some people and not others. The adolescent study suggests that a pre-existing, hidden low B12 may predispose people, and calls for more research.
• The full mechanism. The methionine study shows that low methionine alone does not explain the damage.
• Methionine and folic acid. Whether adding methionine, or folic acid in people with normal folate, changes outcomes is unsettled.
• Long-term outcomes. Most follow-up in these studies runs for months, not years, and the patients are drawn from hospitals, which tilts the picture towards more severe cases. Nearly all the evidence is retrospective case series rather than controlled trials.
• The true number of cases. Poison-centre calls capture only the cases someone reports. The United States authors suggest that the condition is under-recognised.

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Key Research Papers

1. Flippo TS, Holder WD Jr. Neurologic degeneration associated with nitrous oxide anesthesia in patients with vitamin B12 deficiency. Arch Surg. 1993;128(12):1391-5. PubMed PMID: 8250714
2. Garakani A, Jaffe RJ, Savla D, Welch AK, Protin CA, Bryson EO, McDowell DM. Neurologic, psychiatric, and other medical manifestations of nitrous oxide abuse: A systematic review of the case literature. Am J Addict. 2016;25(5):358-69. PubMed PMID: 27037733
3. Zheng R, Wang Q, Li M, Liu F, Zhang Y, Zhao B, Sun Y, Zhang D, Yan C, Zhao Y, Li W. Reversible Neuropsychiatric Disturbances Caused by Nitrous Oxide Toxicity: Clinical, Imaging and Electrophysiological Profiles of 21 Patients with 6-12 Months Follow-up. Neuropsychiatr Dis Treat. 2020;16:2817-2825. PubMed PMID: 33262596
4. Gao H, Li W, Ren J, Dong X, Ma Y, Zheng D. Clinical and MRI Differences Between Patients With Subacute Combined Degeneration of the Spinal Cord Related vs. Unrelated to Recreational Nitrous Oxide Use: A Retrospective Study. Front Neurol. 2021;12:626174. PubMed PMID: 33603713
5. Joncquel Chevalier-Curt M, Grzych G, Tard C, Lannoy J, Deheul S, Hanafi R, Douillard C, Vamecq J. Nitrous oxide abuse in the emergency practice, and Review of toxicity mechanisms and potential markers. Food Chem Toxicol. 2022;162:112894. PubMed PMID: 35219765
6. Oulkadi S, Peters B, Vliegen AS. Thromboembolic complications of recreational nitrous oxide (ab)use: a systematic review. J Thromb Thrombolysis. 2022;54(4):686-695. PubMed PMID: 35759070
7. Gernez E, Deheul S, Tard C, Joncquel M, Douillard C, Grzych G. Plasma Methionine and Clinical Severity in Nitrous Oxide Consumption. Toxics. 2022;11(1):12. PubMed PMID: 36668738
8. Sutherland R, Man N, Brown J, Cairns R, Raubenheimer J, Grigg J, Dawson A, Jamshidi N, Peacock A. Has there been an increase in nitrous oxide use and associated harms in Australia? An analysis of triangulated data sources, 2003-2020. Int J Drug Policy. 2023;121:104178. PubMed PMID: 37776604
9. Mondesert E, Eiden C, Peyriere H, Formoso A, Corti L, Cristol JP, Badiou S. Functional vitamin B(12) deficiency is a consistent feature in hospital admissions for neurological disorders due to the use of nitrous oxide. Clin Toxicol (Phila). 2023;61(9):674-679. PubMed PMID: 37917184
10. Kulkantrakorn K, Chunhachatrachai P, Kulkantrakorn W. Nitrous oxide abuse and associated neurological diseases. BMC Neurol. 2024;24(1):461. PubMed PMID: 39587477
11. Ryder H, Mosalski S, Bramah V, Page R, Faux SG, Shiner CT. Multidisciplinary rehabilitation following recreational nitrous oxide (N(2)O) misuse: evaluating service provision and rehabilitation outcomes in a cohort with serious disability. Disabil Rehabil. 2025;47(5):1204-1213. PubMed PMID: 38950561
12. Temple C, Lin A, Hughes A. Trends in nitrous oxide abuse and misuse: a 22-year analysis of United States poison center data. Clin Toxicol (Phila). 2026;64(4):282-291. PubMed PMID: 41396044
13. White CM, White LR. Nitrous oxide abuse prevalence, mechanisms, treatments and prevention. Curr Med Res Opin. 2026;42(3):451-459. PubMed PMID: 42149724
14. Cohen-Vig L, Hota N, Scheuerman O, Steinberg T, Zeidan M, Genizi J, Rom E, Kogan E, Aharoni S. Recreational nitrous oxide-related myeloneuropathy in adolescents: a multicenter retrospective case series and systematic literature review. Eur J Pediatr. 2026;185(8):591. PubMed PMID: 42474763
15. Bhujel L, Chiew AL, Jagarlamudi B, Chandru P, Gunja N, Briggs N, Chan BS. Relationships among nitrous oxide exposure, neurological injury and biomarkers. Br J Clin Pharmacol. 2026;92(11):3959-3971. PubMed PMID: 42476595

PubMed Topic Searches

1. PubMed: nitrous oxide, myeloneuropathy and vitamin B12
2. PubMed: nitrous oxide and subacute combined degeneration
3. PubMed: the inverted V sign on spinal MRI
4. PubMed: nitrous oxide, homocysteine and methylmalonic acid
5. PubMed: nitrous oxide poison-centre trends

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Connections

• Vitamin B12 Deficiency — the hub for this article
• B12 Nerve Damage and Tingling — nerve damage from every cause of low B12
• B12 Nerve Health and Neuropathy — myelin, methylmalonic acid and recovery
• Subacute Combined Degeneration — the spinal cord disease in full
• How Vitamin B12 Is Absorbed — an interactive animation
• Vitamin B12 — the main topic page

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