Abstract
Background
The recreational use of nitrous oxide (N2O) has seen a worldwide rise in the recent years, resulting in an increased incidence of neurological complications due to N2O-induced functional vitamin B12 deficiency. Here, we report on a cohort of patients admitted to a tertiary care center with neurological symptoms in the context of recreational N2O use between 2020 and 2024.
Methods
We screened the database of the University Hospital Frankfurt for patients ≥ 18 years of age who presented with neurological deficits and a history of N2O consumption between January 2020 and December 2024. We analyzed the spectrum of neurological deficits as well as radiological and laboratory findings.
Results
We identified a total of 20 patients, 16 males and 4 females, with a median age of 21 years. We found a steady increase in the number of cases, with no cases in 2020 and 2021 and a definite peak in 2024. The mean daily N2O consumption was 2500 g. All patients reported sensory deficits; 85% had gait disturbances and 70% had motor deficits. Less frequent symptoms included pain, bladder or bowel dysfunction, fatigue and spasticity. The median score on the modified Rankin scale (mRS) was 2, with some patients being wheelchair-bound. The most frequently observed lesion pattern was combined myelo-polyneuropathy. T2-hyperintense myelon lesions were observed in 11 of 15 patients (73.3%). Surprisingly, laboratory work-up revealed normal vitamin B12 levels in nearly all patients (95%), whereas homocysteine and methylmalonic acid levels were prominently elevated in all patients (100%). In addition, 13 patients (65%) presented with hematological abnormalities. All of the patients who presented for follow-up (20%) reported continued use of N2O. There was no neurological improvement in any of these cases.
Conclusions
Our study confirms that the increasing incidence of N2O-induced neurotoxicity reported in other countries can also be observed in Germany. Therefore, it underlines the relevance of the current debate on health policies. In addition, our study highlights the pitfalls of vitamin B12 laboratory testing and emphasizes the need to address substance addiction in treatment.
Keywords: Nitrous oxide, Polyneuropathy, Myelopathy, Germany
Background
Nitrous oxide (N2O) has been used as an anesthetic with strong analgesic and anxiolytic effects for over 150 years [12]. This substance was already used for recreational purposes in the eighteenth century, e.g. at laughing gas parties. Although the use of N2O has generally been considered safe, it has long been known to damage neurological function through inactivation of vitamin B12, which, in turn, causes neurotoxicity by impairing myelin synthesis [15, 17, 25]. This leads to neurological symptoms, most frequently presenting as paresthesia, peripheral polyneuropathy or subacute combined degeneration of the spinal cord [10, 17]. Myelopathy primarily affects the dorsal columns and pyramidal tracts in the spinal cord. In advanced stages of myelopathy, destruction of the myelin sheaths leads to demyelination with subsequent axonal degeneration [29].
In recent years, there has been a sharp increase in the recreational use of N2O in the EU as well as in the USA and Canada, particularly among people aged 18–24 years [6, 8, 16, 33]. This development is accompanied by a rising incidence of neurological complications in the context of N2O consumption, as shown by recent studies from France and the Netherlands [4, 33].
For Germany, larger case studies are scarce. However, in the past two years, an unprecedented increase in relatively young patients with neurological complications due to vitamin B12 deficiency has been anecdotally reported from several large German cities [19]. Here, we performed a systematic analysis of all patients who were admitted to Frankfurt University Hospital due to N2O-associated neurotoxicity.
Methods
Patient selection
We screened the database of the University Hospital Frankfurt for patients ≥ 18 years who presented with neurological deficits and a history of recreational N2O consumption between January 2020 and December 2024. More specifically, we conducted a keyword search for the terms “nitrous oxide”, “laughing gas”, “vitamin B12”, “hypovitaminosis” or “subacute degeneration of the spinal cord” in both the electronic medical records as well as the radiological database of our department. Basic epidemiological data, neurological symptoms and laboratory results on vitamin B12 metabolism were extracted from clinical records and deidentified. MR imaging of the central nervous system was viewed whenever available.
Data visualization and statistical analysis
For data visualization, we used GraphPad Prism 10.1.2. (Boston, MA, USA) and CorelDRAW Graphics Suite 2019 (Alludo, Ontario, Canada). Statistical analysis was performed with GraphPad Prism 10.1.2 and Microsoft Excel (Microsoft, WA, USA). Unless otherwise indicated, values are given as the means.
Review of the literature
We searched the MEDLINE®-indexed literature using the PubMed search engine from the National Centre for Biotechnology Information (www.pubmed.gov) from January 2010 until February 2025. We used a combined search approach including the following keywords: “nitrous oxide” [MeSH terms]” OR “laughing gas” (MeSH terms) AND “myelopathy” [all fields] OR “neuropathy” [all fields]. We excluded studies with ≤ 5 patients, studies not focusing on neurological disorders and articles that were not publicly available. In addition, we examined the reference list of all identified studies and review articles for studies that might be of relevance.
Results
Patient cohort and nitrous oxide consumption
We identified a total of 20 patients with a history of recreational N2O consumption and neurological symptoms who were treated at the Department of Neurology/University Frankfurt (Table 1). The majority of patients (80%) were male. The median age of the patient cohort was 21 years (range 19–30). Patient interviews did not indicate consumption of other drugs or alcohol abuse. Most of the patients were in an apprenticeship or in a low to middle income job, none had a university degree. The reported amount of consumption of N2O ranged from 40 g to 8000 g per day. The mean daily consumption was 2500 g. Assuming an average quantity of 8 g per container, this corresponds to 312 balloons per day. Notably, two patients reported frequent exposure to N2O but consistently denied active consumption. The median duration of consumption before the first evaluation at our hospital was 11 months, with a range of 1 month to two years.
Table 1.
Basic demographic data and consumption patterns of nitrous oxide
| Sex | Age (years) | Daily consumption | Duration of consumption | Damage pattern |
|---|---|---|---|---|
| Male | 23 | 2000 g | 8 months | Mixed |
| Female | 21 | 4000 g | Several years | Polyneuropathy |
| Male | 19 | Unknown | 12 months | Mixed |
| Male | 20 | Unknown | Unknown | Myelopathy |
| Male | 20 | Unknown | 5 months | Mixed |
| Female | 20 | 3000–5000 g | 12 months | Myelopathy |
| Male | 21 | Passive consumption | 24 months | Mixed |
| Female | 23 | 3000–4000 g | 12 months | Mixed |
| Male | 27 | 5000 g | 9 months | Mixed |
| Male | 28 | 160 g | 18 months | Mixed |
| Male | 23 | 600 g | 1 month | Polyneuropathy |
| Male | 21 | 40 g | Unknown | Mixed |
| Male | 29 | 3000–5000 g | Unknown | Polyneuropathy |
| Female | 20 | 500 g | 10 months | Myelopathy |
| Male | 19 | 2000 g | Unknown | Polyneuropathy |
| Male | 19 | Unknown | Unknown | Myelopathy |
| Male | 24 | 1000–2000 g | 12 months | Polyneuropathy |
| Male | 25 | 2000–8000 g | 2 months | Polyneuropathy |
| Male | 19 | Passive consumption | Unknown | Mixed |
| Male | 23 | 5000 g | 24 months | Myelopathy |
Increasing incidence of nitrous oxide-associated neurotoxicity between 2020 and 2024
During the investigated period from 2020–2024, we observed a significant increase in the number of patients treated with N2O-associated neurotoxicity at our department (Fig. 1). No cases occurred before 2022 according to the database of the hospital. The number of cases then rose noticeably in 2023, and reached a maximum thus far in 2024 with 13 of the 20 cases (65%).
Fig. 1.
Development of the number of cases of nitrous oxide-related neurological symptoms between 2020 and 2024
Clinical findings
All patients complained of sensory deficits (Fig. 2a). Most had additional neurological symptoms, presenting primarily as gait disturbance (85%, n = 17) and/or motor deficits (70%, n = 14). Pain (n = 5), bladder/bowel dysfunction (n = 2), fatigue (n = 2) and spasticity (n = 1) were reported less often. The most frequently observed clinical pattern of N2O-associated neurotoxicity was combined myeloneuropathy (45%), while 30% of the patients had neuropathy, and 25% had myelopathy exclusively (Fig. 2b). We observed no correlation between the quantity or duration of N2O consumption and the damage pattern (Table 1). The clinical severity of the symptoms at the time of the first clinical examination was 2 on the modified Rankin scale (mRS) (Fig. 2c).
Fig. 2.
Clinical findings. a Frequency of neurological symptoms given as a percentage of the entire cohort. The bars in light blue are depicted as percentages of all patients reporting sensory or motor deficits. b Distribution of the damage pattern given as a percentage of the cohort. c Clinical severity quantified by the modified Rankin scale
Imaging and laboratory testing
MR imaging was performed in 15 of the 20 patients (75%). Among these patients, 11 (73.3%) had pathological hyperintensity in the T2-weighted sequences in the posterior funiculi of the spinal cord (Fig. 3a), indicating subacute combined degeneration of the spinal cord (formerly referred to as funicular myelosis). The level of vitamin B12 was within the normal or lower-normal range in all but one patient (Fig. 3b). Three patients even had significantly elevated vitamin B12 levels, which was due to self-initiated substitution prior to admission to our clinic. These patients had no particular dietary habits or other substance dependencies. All patients had normal values for transcobalamine I. In contrast, homocysteine and methylmalonic acid were well above the upper limit of normal in all 20 patients. Thirteen out of 20 patients (65%) had at least one hematological abnormality. These included alterations in the mean corpuscular hemoglobin (MCH), volume (MCV) or red cell distribution width (RCDW) (Fig. 3c). No patient had low hemoglobin levels.
Fig. 3.
Diagnostic findings. a Representative T2-weighted MR image of the upper spine showing hyperintense lesions of the posterior funiculi (inverted “v” sign). b Results of the laboratory work-up of vitamin B12 metabolism. The reference ranges are marked in blue. c Results of the laboratory hemoglobin, mean corpuscular volume and hemoglobin and red cell distribution width. The reference ranges are marked in blue
Treatment and follow-up
All patients were treated with 1000 µg of vitamin B12 per day i.m. for 10 days followed by 1000 μg of vitamin B12 weekly or monthly. We recommend determining the dosage and duration of treatment on the basis of the level of methylmalonic acid at follow-up. Of note, only 4 of the 20 patients (20%) presented for a neurological follow-up examination in our department within three months after discharge. None of these four patients experienced any improvement in their clinical condition. Notably, all four patients continued to use N2O.
Discussion
The rising popularity of recreational nitrous oxide use
Between 2020 and 2024, we observed an unprecedented increase in relatively young adults who presented with N2O-induced neurological symptoms. This coincides with an increased consumption of N2O among adolescents in the catchment area of our hospital as evidenced by a recent urban drug report [21, 22]. In this report, the lifetime prevalence of N2O increased from 7% in 2020 to 17% in 2022 [22] and 14% in 2023 [23]. More than 60% of the survey participants reported high popularity of this substance among their peers. The increase in the recreational use of N2O has been reported by other European countries and worldwide [5, 6].
In our cohort, 80% were male and had a median age of 21 years. This finding is in line with the majority of studies published on recreational N2O use between 2010 and 2025 (Table 2). Specifically, 17 out of 24 studies had a majority of male patients and the median age across all studies was 22 years. Studies from France and the Netherlands have identified a low level of education, employment in the low-wage sector or unemployment as factors that predict a high prevalence of laughing gas consumption [4, 32]. In addition, surveys from the Netherlands have found that consumers often had a non-Dutch background. It must be emphasized that socioeconomic data was rarely collected in the studies we identified. Hence, representative surveys at national level are needed to better understand the socioeconomic and cultural background of the consumers.
Table 2.
Summary of studies on N2O-induced neurotoxicity between 2010 and 2025
| Gao et al Front Neurol 2023 |
Meißner et al NRP 2025 |
Fang et al J Clin Neurol 2023 |
Keddie et al J Neurol 2018 |
Bao et al Neuropsychiatr Dis Treat 2020 |
Tuan et al Neurol Int 2020 |
Zheng et al., Neuropsychiatr Dis Treat 2020 |
Zhang et al., Front Neurol 2021 |
Vollhardt et al., J Neurol 2021 |
|
|---|---|---|---|---|---|---|---|---|---|
| Year of recruitment | 2016–2021 | 2020–2024 | 2018–2020 | 2016–2017 | 2015–2019 | 2018–2019 | 2016–2019 | 2018–2020 | 2020–2021 |
| Country | China | Germany | China | England | China | Vietnam | China | China | France |
| Number of patients | 20 | 23 | 76 | 10 | 33 | 47 | 21 | 20 | 12 |
| Age (mean, range) | 22 (16–30) | 25 | 21 (14–33) | 22 (median) (17–26) | 22 (14–27) | 24 (15–50) | 23 (15–34) | 23 (median)(20–28) | 22 (17–28) |
| Sex | |||||||||
| Male | 25% | 65% | 45% | 70% | 88% | 49% | 67% | 55% | 50% |
| Female | 75% | 35% | 55% | 30% | 12% | 51% | 33% | 45% | 50% |
| Exposure time to N2O | 7 months | NR | 12 months | NR | 18 ± 4.3 months | 8.8 months | 7.2 months | NR | 12.7 months |
| Pattern of N2O use | NR | 83% regular consumption (15/18) | NR |
2–3 days/week (average); 72–2000 canisters/week |
NR | 3.2 days/week, 36 balloons/day | NR | NR | 3,109 ± 2,800 g/week (mean) |
| Clinical syndrom | |||||||||
| Sensory deficit | 70% | 96% | 98% | 100% | 91% | 100% | 86% | 95% | 92% |
| Motor deficit | 95% | 52% | 79% | 50% | 82% | 87% | 90% | 80% | 75% |
| Gait disturbance | 95% | 83% | 42% | 80% | 46% | – | – | 20% | – |
| Bladder/bowel | 5% | – | 17% | 10% | 6% | – | – | 5% | 50% |
| Decreased reflexes | 100% | 74% | 59% | 50% | 85% | 85% | 67% | – | 83% |
| Increased reflexes | – | – | – | 30% | 15% | – | 10% | – | – |
| Spasticity/UMN* | – | 13% | 13% | 30% | – | – | – | – | 8% |
| Damage pattern | |||||||||
| Myelopathy | NA | 60% (14/21) | 56% (20/36) | 100% (9/9) | 48% | 68% | 47% (8/17) | 79% (15/19) | 75% |
| Neuropathy | 100% (15/15) | 87% | NR | NR | 100% | NR | 85% (17/20) | 89% (16/18) | 83% |
| Hematology | |||||||||
| Low Hb | 40% (4/10) | 26% (6/23) | 86% (44/51) | NR | 6% | 32% | 10% (2/20) | 15% | NR |
| Increased MCV | 20% (2/10) | NR | 34% (15/44) | 0% | 6% | NR | 15% (3/20) | 25% | NR |
| Vitamin B12 deficiency | 57% (4/7) | 35% (8/23) | 64% (28/44) | 40% | 27% | 57% | 17% (3/18) | 39% (5/13) | 42% |
| Increased Hcy | 60% (3/5) | 89% (8/9) | 71% (25/35) | NR | 82% | 87% | 78% (14/18) | 88% (14/16) | 100% (11/11) |
| Increased MMA | NR | 95% (18/19) | NR | 88% (7/8)** | NR | NR | NR | NR | 100% (11/11) |
| Outcome | |||||||||
| Improvement at discharge | 75% (15/20) | NR | NR | NR | NR | NR | 100% | 80% | NR |
| Improvement at follow-up | NR | NR | NR | NR | |||||
| Complete | – | 30% (2/6) | 80% (4/5) | 94% (16/17) | – | ||||
| Partial | 43% (3/7) | 50% (3/6) | 20% (1/5) | 6% (1/17) | 100% (8/8) | ||||
| None | 57% (4/7) | 20% (1/6) | – | – | – | ||||
| Nugteren-Van Lonkhuyzen et al. [24] | Cruz et al Eur J Neurol.2024 |
Soderstrom et al Druc Alcohol Rev 2024 |
Dabby et al Isr Med Assoc J. 2024 |
Van Riel et al Int J Drug Policy 2022 |
B J Rujiter et al J Neurol.2024 |
Hassing et al Eur J Neurol. 2024 |
Dawudi et al J Neurol 2024 |
Fortanier et al Eu J Neurol 2023 |
|
|---|---|---|---|---|---|---|---|---|---|
| Year of recruitment | 2021–2022 | 2020–2024 | 2019–2021 | 2022–2023 | 2010–2020 | 2016–2021 | 2018–2021 | 2018–2021 | 2020–2023 |
| Country | The Netherlands | France | Australia | Israel | The Netherlands | The Netherlands | The Netherlands | France | France |
| Number of patients | 101 | 61 | 22 | 8 | 433 | 251 | 70 | 181 | 58 |
| Age (mean, range) | 23 (16–26) (median) | 24 | 22 (median) (20–50) | 21 (median) (17–32) | 22 (median) | 22 (IQR 20–26) | 22 (median) (18–50) | 23 | 23 |
| Sex | |||||||||
| Male | 52% | 62% | 68% | 62% | 64% | 63% | 64% | 54% | 67% |
| Female | 48% | 38% | 32% | 38% | 36% | 37% | 36% | 46% | 33% |
| Exposure time to N2O | NR | 9 months | 9 months | NR | NR | 11 months | 12 months | 6 months | 8.7 ± 5.2 months |
| Consumption pattern | 77% heavy use (> 50 balloons in one session or use from a tank) | 4–19 600-g-cylinders/week (median) | 150 N2O bulbs/day (median) | NR | 59% heavy use (> 50 balloons in one session or use from a tank) | 1.6 kg per day (0.5–4.0 kg) | 4 kg/week | 1200 g/day (average) | 10.8 ± 11.6 L/week |
| Clinical syndrom | NR | NR | NR | ||||||
| Sensory deficit | 41% | 63% | 63% | 97% | 98% | 100% | |||
| Motor deficit | 13% | 22% | 25% | 57% | 72% | 60% | |||
| Gait disturbance | 9% | 59% | 75% | 77% | 84% | 88% | |||
| Bladder/bowel | – | 14% | – | 20%/10% | 19% | 28% | |||
| Decreased reflexes | – | – | 13% | 67% | – | 74% | |||
| Increased reflexes | – | – | 25% | 9% | – | – | |||
| Spasticity/UMN* | – | – | – | 9% | – | 3%– | |||
| Damage pattern | |||||||||
| Myelopathy | NR | 79% (42/53) | 55% | 63% | NR | 41% | 55% | 63% | 54% (26/48) |
| Neuropathy | 41% | 66% (35/53) | NR | 38% | NR | 78% | 81% | 75% | NR |
| Hematology | NR | NR | NR | NR | NR | NR | NR | NR | |
| Low Hb | 9% (5/57) | ||||||||
| Increased MCV | |||||||||
| Vitamin B12 deficiency | NR | NR | 55% | 75% | NR | 40% | 50% (34/67) | NR | 51% |
| Increased Hcy | 93% (15/16) | 85% (6/7) | 92% (109/118) | – | 96% | ||||
| Increased MMA | NR | 100% (5/5) | NA | – | NR | ||||
| Outcome | |||||||||
| Improvement at discharge | NR | NR | NR | 100% | NR | NR | NR | NR | NR |
| Improvement at follow-up | NR | NR | NR | NR | 79% partial or complete recovery (80/102) | NR | |||
| Complete | 86% (6/7) | 31% (16/52) | 8% (5/64) | ||||||
| Partial | 14% (1/7) | 50% (26/52) | |||||||
| None | 19% (10/52) | ||||||||
| Qin et al J peripher Nerv Syst, 2022 |
Largeau et al Eur J Neurol 2022 |
Li et al Brain Behav 2021 |
Jiang et al Brain behav, 2021 |
Swart et al Eur J Neurol 2021 |
Yu et al Brain Behav. 2022 |
|
|---|---|---|---|---|---|---|
| Year of recruitment | 2019 -2020 | 2019–2020 | 2017–2020 | 2017–2020 | 2016–2020 | 2018–2020 |
| Country | China | France | China | China | Australia | China |
| Number of patients | 15 | 20 | 61 | 63 | 20 | 110 |
| Age (mean, range) | 22 (19–33) | 19 (median) (16–34) | 22 | 23 (15–33) | 24 (18–40) | 21 (14–33) |
| Sex | ||||||
| Male | 47% | 85% | 69% | 60% | 45% | 52% |
| Female | 53% | 15% | 31% | 40% | 55% | 48% |
| Exposure time to N2O | 2.5 months | 6 months | 8.5 ± 7.7 months | NR | 9 months | 12.5 ± 4.2 months |
| Consumption pattern | 26 canisters/month (median) | 100 cartridges/day; 58% showed daily exposure | NR | 4000 (2400 − 7000) ml per session, intake frequency 3.33 ± 1.69 times per week | 148 canisters/day (averaged) | NR |
| Clinical syndrom | ||||||
| Sensory deficit | 100% | 100% | 80% | 100% | 100% | 80% |
| Motor deficit | 100% | 25% | 57% | 43%- | 45% | 83% |
| Gait disturbance | 53% | 100% | 66% | 97% | 100% | – |
| Bladder/bowel dysfunction | – | – | 8% | - | 20% | 10% |
| Decreased reflexes | 60% | – | 49% | 47% | 15% | 71% |
| Increased reflexes | 20% | – | 10% | – | 15% | 9% |
| Spasticity/UMN* | 53% | – | 23% | 36% | 15% | 7% |
| Damage pattern | NR | |||||
| Myelopathy | 64% (7/11) | 49% | 60% | 100% (20/20) | 52% (25/50) | |
| Neuropathy | 36% (4/11) | 80% | 81% | 100% (6/6) | 100% (87/87) | |
| Hematology | ||||||
| Low Hb | NR | NR | 5% | 20% | 45% | 35% (25/71) |
| Increased MCV | NR | 22% | NR | 20% (5/25) | ||
| Vitamin B12 deficiency | 33% (3/9) | 64% (9/14) | 44% (20/45) | 35% | 50% | 60% (34/57) |
| Increased Hcy | NR | 100% (13/13) | 68% (27/40) | 87% | 83% (10/12) | 69% (31/45) |
| Increased MMA | NR | 100% (7/7) | NR | NR | NR | NR |
| Outcome | ||||||
| Improvement at discharge | NR | NR | NR | NR | NR | NR |
| Improvement at follow-up | NR | NR | ||||
| Complete | 87% | 95% (58/61) | 13% (1/8) | 67% (34/51) | ||
| Partial | 13% | 5% (3/61) | 87% (7/8) | 33% (17/51) | ||
| None | – | – | – | 2% (1/51) | ||
UMN = upper motor neuron; NR = not reported; NA = not publicly available; Hcy = homocysteine; MMA = methylmalonic acid; MCV = mean corpuscular volume
*Including positive Babinski sign
**Assessed only in patients with normal vitamin B12 levels
The rising popularity of N2O worldwide has been attributed in part to its perception as a harmless substance [21, 23] as well as to its easy-access supply, e.g., through online shops and kiosks [6, 21]. A recent development is the sale of large cylinders of up to 2 kg, allowing for heavy use at reduced costs. In a recent study from France involving 181 patients between 2019 and 2021, the average daily consumption was 1200 g [4]. Notably, the authors reported that this number was 27,000 times greater than that reported in 2017 for the same urban area. In our cohort, 85% of the patients with active use consumed ≥ 400 g/day, and the mean daily consumption was 2500 g. Hence, the growing number of patients presenting with neurological sequelae from N2O use could also result from a subgroup of users with excessive daily intake. Nevertheless, cases of neurological damage resulting from infrequent or passive consumption have also been reported [28, 30], which was also observed in our study. Consequently, no safe level of use can be defined at this point.
In our literature search, it was striking that nitrous oxide consumption was either not reported at all or that consumption was quantified in very heterogeneous units, which limited comparability. Some of the authors reported that patients did not want to provide any information on their consumption or that the information given was very vague. Clinicians should take this into account when taking the patient’s medical history.
Diagnostic findings
A crucial aspect for clinical management is the diagnosis at the earliest timepoint. From a clinical point of view, sensory deficits (hyp-/paresthesia) are the most common, often accompanied by gait disturbance, muscle weakness and reduced muscle reflexes (Table 2, Fig. 2). It is therefore not surprising that subacute polyneuropathy is often assumed as the initial differential diagnosis [9]. Myelopathy was present in about every second patient in our literature search. However, symptoms that suggest damage of the CNS (e.g. spasticity, increased tendon reflexes or pathologic reflexes) were often not detectable.
It has been reported that the neurotoxicity of N2O is dose dependent [34]. Furthermore, the patterns of use could impact the clinical symptoms of patients in that the effect on the spinal cord is dependent on the quantity of N2O, whereas the presence of polyneuropathy may depend on the duration of exposure to N2O [3]. We did not observe such a correlation in our cohort, although this could be due to the limited number of cases.
In the case of suspected or confirmed nitrous oxide consumption, the diagnostic work-up primarily includes laboratory evaluation for vitamin B12 metabolism. However, the use of vitamin B12 levels for diagnosis remains problematic because of its low specificity. Although studies have shown reduced vitamin B12 levels in up to 70% of consumers [26, 35], our literature search underlines that total circulating vitamin B12 is not a reliable indicator of nitrous oxide-induced neurological disorders. Low vitamin B12 levels varied between 17% and 75%. In our cohort, only one patient (5%) had low vitamin B12 levels. In addition, it must be emphasized that in some studies, including ours, patients had already started self-treatment with vitamin B12 before seeking medical help. Thus, relying on vitamin B12 levels can mask the functional impairment of vitamin B12 metabolism.
The inactivation of vitamin B12 by N2O incapacitates the enzymatic activity of methylmalonyl-CoA-mutase and methionine synthase, resulting in the accumulation of both methylmalonic acid and homocysteine [2]. In all studies in which both vitamin B12 and homocysteine were examined, homocysteine was significantly more frequently elevated. This is in line with our own findings, as well as a recent review [20]. Hence, homocysteine and methylmalonic acid are much more reliable markers for N2O-induced disruption of vitamin B12 metabolism and for monitoring treatment success [11, 20]. Since the analysis of methylmalonic acid is costly, homocysteine is usually preferred. This is reflected in the results of our literature search: methylmalonic acid was only examined in 5 of 24 studies. Whether homocysteine or methylmalonic acid are indicative of the mechanisms of N2O-induced neurotoxicity is still under investigation [13].
Treatment and outcome
The cornerstone of treatment is vitamin B12 supplementation. There is a consensus that supplementation should initially be carried out at high intensity, although there are different schemes for implementation. It is recommended that the substitution is initially carried out daily [14] or every other day [27] via i.m. injections of 1000 µg of hydroxycobalamin over the course of one to two weeks or until there is no further improvement of symptoms. Supplementation can then be reduced to a weekly or 3-monthly dose, depending on whether the patient had a pre-existing vitamin B12 deficiency.
There are little data on long-term follow-up, which is reflected in our literature search. In almost all studies that reported on the clinical outcome, including ours, a high rate of loss to follow-up was observed. Furthermore, information on N2O abstinence was frequently missing.
Overall, a high percentage of patients show some neurological improvement (Table 2), either at discharge or at follow-up. In the 13 studies with follow-up, the percentage of complete recovery ranged from 0 to 95%. In a Chinese review with 51 patients at follow-up, 67% recovered completely whereas 33% had residual symptoms [35]. Notably, this study recorded only one relapse during the observation period. In two systematic case reviews, partial recovery was most frequently observed [10, 18], and progression of the disease was only seen if patients continued consumption. This could explain the poor outcome of our follow-up patients and emphasizes that cessation of N2O consumption is crucial for recovery [18].
Reports of excessive recreational use have foregrounded the debate of whether N2O has addictive potential. Previous studies have shown that the majority of heavy users show symptoms of substance use disorders, with up to 90% reporting the use of N2O in larger quantities and for longer periods than intended [1, 7, 24]. In addition to psychological addiction, reports have shown that frequent users tend to inhale larger quantities over time to experience similar physical effects [31]. In our cohort, all patients who presented for follow-up continued to use N2O despite their considerable neurological deficits. In a Dutch study, 80% of the participants unsuccessfully tried to cease N2O use [24]. This highlights the need to address substance addiction in treatment.
Conclusions
In summary, the increasing number of patients presenting with neurological sequelae from the use of N2O could be a result of several factors, including its rising popularity, low costs, excessive intake fueled by widespread availability, and the addictive potential of the gas. These aspects explain why some countries, e.g. France and the Netherlands, have introduced health policy changes that strongly restrict open access to N2O [5]. In Germany, changes in legislation have not yet been implemented. Our study from a tertiary care center in Germany confirms the increasing incidence of N2O-induced neurotoxicity especially in young adults that has been observed in other countries. It therefore underlines the relevance of the current health policy debate. Target group-specific measures to raise awareness of the health risks appear necessary, for example via social media or schools. The high median daily consumption in our cohort and the continued use observed at follow-up stress the addictive potential of N2O. Addiction counseling should therefore be an integral part of treatment.
Acknowledgements
Not applicable.
Abbreviations
- MCH
Mean corpuscular hemoglobin
- MCV
Mean corpuscular volume
- mRS
Modified Rankin scale
- N2O
Nitrous oxide
- RCDW
Red cell distribution width
Author contributions
Conceptualization: AT, CG, MH and ID. Data acquisition: AT, SJY, CG, EH, MH and ID. Analysis and interpretation of data: all authors. Data visualization: ID. Writing of the original draft: AT and ID. Review and final editing of the manuscript: all authors.
Funding
Open Access funding enabled and organized by Projekt DEAL. No funding was received for this study.
Availability of data and materials
All data generated or analyzed during this study are included in this published article.
Declarations
Ethics approval and consent to participate
The study, including the data collection and publication in anonymized form, was approved by the Ethical Committee at the University Hospital Frankfurt (project no. 2024–1942).
Consent for publication
Not applicable.
Competing interests
JPS has received honoraria for presentations, educational events and advisory board participation from GSK, Boehringer Ingelheim, Med-Update, Roche, Novocure, Seagen, Servier and Med-Update. All other authors declare that they have no competing interests.
Footnotes
Publisher's Note
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References
- 1.Back, S., Kroon, E., Colyer-Patel, K., & Cousijn, J. (2024). Does nitrous oxide addiction exist? An evaluation of the evidence for the presence and prevalence of substance use disorder symptoms in recreational nitrous oxide users. Addiction (Abingdon, England),119(4), 609–618. 10.1111/add.16380 [DOI] [PubMed] [Google Scholar]
- 2.Chanarin, I. (1982). The effects of nitrous oxide on cobalamins, folates, and on related events. Critical Reviews in Toxicology,10(3), 179–213. 10.3109/10408448209037455 [DOI] [PubMed] [Google Scholar]
- 3.Cruz, E. S., Fortanier, E., Hilezian, F., Maarouf, A., Boutière, C., Demortière, S., Rico, A., Delmont, E., Pelletier, J., Attarian, S., & Audoin, B. (2024). Factors affecting the topography of nitrous oxide-induced neurological complications. European Journal of Neurology,31(7), e16291. 10.1111/ene.16291 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Dawudi, Y., Azoyan, L., Broucker, T. D. E., Gendre, T., Miloudi, A., Echaniz-Laguna, A., Mazoyer, J., Zanin, A., Kubis, N., Dubessy, A.-L., Gorza, L., Ben Nasr, H., Caré, W., d’Izarny-Gargas, T., Formoso, A., Vilcu, A.-M., & Bonnan, M. (2024). Marked increase in severe neurological disorders after nitrous oxide abuse: A retrospective study in the Greater Paris area. Journal of Neurology,271(6), 3340–3346. 10.1007/s00415-024-12264-w [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.European Monitoring Centre for Drugs and Drug Addiction. European Drug Report 2024: Trends and Developments. https://www.euda.europa.eu/publications/european-drug-report/2024_en
- 6.European Monitoring Centre for Drugs and Drug Addiction 2022. Recreational use of nitrous oxide: a growing concern for Europe. https://www.euda.europa.eu/publications/rapid-communication/recreational-use-nitrous-oxide-growing-concern-europe_en
- 7.Fidalgo, M., Prud’homme, T., Allio, A., Bronnec, M., Bulteau, S., Jolliet, P., & Victorri-Vigneau, C. (2019). Nitrous oxide: What do we know about its use disorder potential? Results of the french monitoring centre for addiction network survey and literature review. Substance Abuse,40(1), 33–42. 10.1080/08897077.2019.1573210 [DOI] [PubMed] [Google Scholar]
- 8.Forrester, M. B. (2021). Nitrous oxide misuse reported to two United States data systems during 2000–2019. Journal of Addictive Diseases,39(1), 46–53. 10.1080/10550887.2020.1813361 [DOI] [PubMed] [Google Scholar]
- 9.Fortanier, E., Berling, E., Zanin, A., Le Guillou, A., Micaleff, J., Nicolas, G., Lozeron, P., & Attarian, S. (2023). How to distinguish Guillain-Barré syndrome from nitrous oxide-induced neuropathy: A 2-year, multicentric, retrospective study. European Journal of Neurology,30(10), 3296–3306. 10.1111/ene.15998 [DOI] [PubMed] [Google Scholar]
- 10.Garakani, A., Jaffe, R. J., Savla, D., Welch, A. K., Protin, C. A., Bryson, E. O., & McDowell, D. M. (2016). Neurologic, psychiatric, and other medical manifestations of nitrous oxide abuse: A systematic review of the case literature. The American Journal on Addictions,25(5), 358–369. 10.1111/ajad.12372 [DOI] [PubMed] [Google Scholar]
- 11.Gernez, E., Lucas, A., Niguet, J.-P., Bennis, A., Diesnis, R., Noyce, A. J., & Grzych, G. (2024). What biological markers could be used for diagnosis and monitoring of nitrous oxide abuse? European Journal of Neurology,31(3), e16188. 10.1111/ene.16188 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Gillman, M. A. (2019). Mini-review: A brief history of nitrous oxide (n2o) use in neuropsychiatry. Current Drug Research Reviews,11(1), 12–20. 10.2174/1874473711666181008163107 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Grzych, G., Scuccimarra, M., Plasse, L., Gernez, E., Cassim, F., Touze, B., Girot, M., Bossaert, C., & Tard, C. (2024). Understanding neuropathy features in the context of nitrous oxide abuse: A combined electrophysiological and metabolic approach. Biomedicines. 10.3390/biomedicines12020429 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.de Halleux, C., & Juurlink, D. N. (2023). Diagnosis and management of toxicity associated with the recreational use of nitrous oxide. CMAJ: Canadian Medical Association Journal= Journal De L’association Medicale Canadienne,195(32), E1075–E1081. 10.1503/cmaj.230196 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Hathout, L., & El-Saden, S. (2011). Nitrous oxide-induced B₁₂ deficiency myelopathy: Perspectives on the clinical biochemistry of vitamin B₁₂. Journal of the Neurological Sciences,301(1–2), 1–8. 10.1016/j.jns.2010.10.033 [DOI] [PubMed] [Google Scholar]
- 16.Kaar, S. J., Ferris, J., Waldron, J., Devaney, M., Ramsey, J., & Winstock, A. R. (2016). Up: The rise of nitrous oxide abuse. An international survey of contemporary nitrous oxide use. Journal of Psychopharmacology (Oxford England),30(4), 395–401. 10.1177/0269881116632375 [DOI] [PubMed] [Google Scholar]
- 17.Layzer, R. B. (1978). Myeloneuropathy after prolonged exposure to nitrous oxide. Lancet (London, England),2(8102), 1227–1230. 10.1016/S0140-6736(78)92101-3 [DOI] [PubMed] [Google Scholar]
- 18.Marsden, P., Sharma, A. A., & Rotella, J.-A. (2022). Review article: Clinical manifestations and outcomes of chronic nitrous oxide misuse: A systematic review. Emergency Medicine Australasia : EMA,34(4), 492–503. 10.1111/1742-6723.13997 [DOI] [PubMed] [Google Scholar]
- 19.Meißner, J. N., Neuneier, J., Bartzokis, I., Rehm, M., Al-Hayali, A., Müller, M., Paus, S., Limmroth, V., Fink, G. R., Petzold, G. C., & Nitsch, L. (2025). Increase of nitrous oxide-induced neurological disorders - a German multicenter experience. Neurological Research and Practice,7(1), 3. 10.1186/s42466-024-00361-0 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20.Ménétrier, T., & Denimal, D. (2023). Vitamin B12 status in recreational users of nitrous oxide: A systematic review focusing on the prevalence of laboratory abnormalities. Antioxidants (Basel, Switzerland). 10.3390/antiox12061191 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.MoSyD 2022. Monitoring system drogentrends. https://www.uni-frankfurt.de/146663665/MoSyD_Jahresbericht_2022_final.pdf
- 22.MoSyD 2023. Monitoring system drogentrends. https://www.frankfurt-university.de/fileadmin/standard/ISFF/MoSyD-Jahresbericht_2023_final.pdf
- 23.Nabben, T., Weijs, J., & van Amsterdam, J. (2021). Problematic Use of Nitrous Oxide by Young Moroccan-Dutch Adults. International Journal of Environmental Research and Public Health. 10.3390/ijerph18115574 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24.Nugteren-Van Lonkhuyzen, J. J., van der Ben, L., van den Hengel-Koot, I., & S, Lange de, DW., Riel van, A. J. H. P., & Hondebrink, L,. (2023). High Incidence of Signs of Neuropathy and Self-Reported Substance Use Disorder for Nitrous Oxide in Patients Intoxicated with Nitrous Oxide. European Addiction Research,29(3), 202–212. 10.1159/000530123 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 25.Nunn, J. F. (1984). Interaction of nitrous oxide and vitamin B12. Trends in Pharmacological Sciences,5, 225–227. 10.1016/0165-6147(84)90426-7 [Google Scholar]
- 26.Oussalah, A., Julien, M., Levy, J., Hajjar, O., Franczak, C., Stephan, C., Laugel, E., Wandzel, M., Filhine-Tresarrieu, P., Green, R., & Guéant, J.-L. (2019). Global burden related to nitrous oxide exposure in medical and recreational settings: A systematic review and individual patient data meta-analysis. Journal of Clinical Medicine. 10.3390/jcm8040551 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Paris, A., Lake, L., Joseph, A., Workman, A., Walton, J., Hayton, T., Evangelou, N., Lilleker, J. B., Ayling, R. M., Nicholl, D., & Noyce, A. J. (2023). Nitrous oxide-induced subacute combined degeneration of the cord: Diagnosis and treatment. Practical Neurology,23(3), 222–228. 10.1136/pn-2022-003631 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28.Patel, K. K., Mejia Munne, J. C., Gunness, V. R. N., Hersey, D., Alshafai, N., Sciubba, D., Nasser, R., Gimbel, D., Cheng, J., & Nouri, A. (2018). Subacute combined degeneration of the spinal cord following nitrous oxide anesthesia: A systematic review of cases. Clinical Neurology and Neurosurgery,173, 163–168. 10.1016/j.clineuro.2018.08.016 [DOI] [PubMed] [Google Scholar]
- 29.Renard, D., Dutray, A., Remy, A., Castelnovo, G., & Labauge, P. (2009). Subacute combined degeneration of the spinal cord caused by nitrous oxide anaesthesia. Neurological Sciences,30(1), 75–76. 10.1007/s10072-009-0013-2 [DOI] [PubMed] [Google Scholar]
- 30.Sluyts, Y., Pals, P., Amir, R., & Vanherpe, P. (2021). Recreational use of nitrous oxide may cause collateral neurological damage. Acta Neurologica Belgica,121(4), 1097–1099. 10.1007/s13760-021-01740-z [DOI] [PubMed] [Google Scholar]
- 31.van Amsterdam, J., Nabben, T., & van den Brink, W. (2015). Recreational nitrous oxide use: Prevalence and risks. Regulatory Toxicology and Pharmacology : RTP,73(3), 790–796. 10.1016/j.yrtph.2015.10.017 [DOI] [PubMed] [Google Scholar]
- 32.van den Toren, S. J., van Grieken, A., & Raat, H. (2021). Associations of socio-demographic characteristics, well-being, school absenteeism, and substance use with recreational nitrous oxide use among adolescents: A cross-sectional study. PLoS ONE,16(2), e0247230. 10.1371/journal.pone.0247230 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 33.van Riel, A. J. H. P., Hunault, C. C., van den Hengel-Koot, I. S., Nugteren-van Lonkhuyzen, J. J., de Lange, D. W., & Hondebrink, L. (2022). Alarming increase in poisonings from recreational nitrous oxide use after a change in EU-legislation, inquiries to the Dutch Poisons Information Center. The International Journal on Drug Policy,100, 103519. 10.1016/j.drugpo.2021.103519 [DOI] [PubMed] [Google Scholar]
- 34.Winstock, A. R., & Ferris, J. A. (2020). Nitrous oxide causes peripheral neuropathy in a dose dependent manner among recreational users. Journal of Psychopharmacology (Oxford, England),34(2), 229–236. 10.1177/0269881119882532 [DOI] [PubMed] [Google Scholar]
- 35.Yu, M., Qiao, Y., Li, W., Fang, X., Gao, H., Zheng, D., & Ma, Y. (2022). Analysis of clinical characteristics and prognostic factors in 110 patients with nitrous oxide abuse. Brain and Behavior,12(4), e2533. 10.1002/brb3.2533 [DOI] [PMC free article] [PubMed] [Google Scholar]
Associated Data
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Data Availability Statement
All data generated or analyzed during this study are included in this published article.