Laughing gas is no laughing matter: How recreational use endanger lives in traffic

Anders Valentin A. Nielsen, M.D., Ph.d. student
Published 5 Nov 2025

Laughing gas (Nitrous oxide: N2O) is a euphoric and sedating gas that is used in both medical and recreational settings. It poses a particular danger when combined with driving. This is an increasing problem for law enforcement. Previously, it was believed that N2O was eliminated so quickly from the body that a sample to prove intake could not be obtained in time. However, Anders Nielsen and colleagues from the Institute of Forensic Medicine, Aarhus University, challenge this old dogma in an ongoing study.

New study to assist law enforcement in keeping the roads safe

Preliminary results from Aarhus University show that N₂O can be detected for longer than previously believed, taking the detection window from half an hour to several hours. However, to the greatest practicable extent, the sooner the evidence material is secured, the better.

Researchers evaluated exhaled air, blood, saliva, urine and a handheld N₂O sensor, to explore which biological samples are best for detecting N₂O. The sensor can be used roadside at the point of arrest, akin to an alcohol breathalyzer.

A placebo-controlled study with 30 healthy volunteers was undertaken. The need for a control group was twofold:

Trace amounts of N₂O are present in the atmosphere and therefore also in humans. A baseline for non-exposed individuals was therefore needed.
The control group allowed researchers to test the reliability of the screening device in distinguishing between non-exposed and N₂O- exposed individuals.

Air and saliva samples can be collected roadside in gas- tight bags and vials, while blood and urine require transport to the nearest hospital to get a sample, costing potentially precious time for N₂O to be eliminated from the body. Law enforcement and researchers are joining forces to solve this complex challenge.

Fatal traffic accidents involving N₂O

Sadly, several people have been killed due to a driver inhaling N₂O and causing a traffic accident in Denmark. For now, N₂O is not on the list of illegal euphoric drugs, so it is technically not illegal for a driver to have N₂O in the blood while driving. A process to change this law is currently being undertaken.

An illustration of the entire sequence of events in an N₂O related traffic accident is illustrated below. After screening with a handheld device, a confirmatory test is needed. At present, it is unclear whether blood, exhaled air, or saliva is most suitable for this purpose.

Laughing gas traffic process — Illustration of the entire course of a traffic accident involving N2O: 1) An intoxicated driver accidently collides with an elderly person. 2) First responders initiate potential lifesaving treatment as the driver is apprehended. 3) The person dies from the injuries sustained in the crash. Law enforcement performs a screening for the presence of N2O in the breath of the driver, which is positive. 4) The driver is taken to hospital to have a confirmatory blood test, which is analyzed in a forensic laboratory and the results are used to argue that inhalation of N2O during driving was an aggravating circumstance in this case in a court of law.

Conclusion

This new discovery increases law enforcement’s capabilities to prove N₂O intake. This enhanced capability can help provide closure to the next of kin by confirming that N₂O was the cause of the accident. Additionally, if drivers are aware they can be convicted of driving under the influence of N₂O, it might deter some recreational users from driving under its influence, which contributes to safer roads for all in society. However, a change in the law of Denmark is still required before it is publishable.

Disclaimer: This research is financially supported by The Victims’ fund (Offerfonden). The assessments and viewpoints expressed in the material are those of the authors and do not necessarily reflect those of the Council for the Victims’ Fund.

The article is written by

Anders Valentin A. Nielsen

M.D., Ph.d. student

Aarhus University

Department of Forensic Medicine

on the request of PopNAD