Laughing gas is becoming a popular recreational drug, say doctors, who warn of potential health risks from its use.
No laughing matter: Drug can cause health problems
A survey in New Zealand found one in eight students at a university had used nitrous oxide recreationally.
Cannisters of nitrous oxide are used in some domestic appliances - for example cream dispensing containers - and can be bought easily at hardware stores.
Inhaling the gas can produce hallucinations and disorientation - and overuse has been linked to long-term health problems.
The survey, published in the medical journal The Lancet, involved 1,782 first-year students at the University of Auckland.
More than half of the students said they were aware that nitrous oxide could be used recreationally.
Approximately 12% said they had used it recreationally at some point, and 3% - 39 students - said they were regular users.
The authors of the study said that the findings - while not necessarily representative of the population at large - should alert doctors to watch out for nitrous oxide-linked problems in young people.
In particular, heavy nitrous oxide use has been linked to depletion of vitamin B12 and a temporary loss of motor control.
One case reported by the Lancet involved degeneration of the spinal cord linked to its use.
I wouldn't claim it was a particularly harmful drug - but I wouldn't say it was completely without harm as well
The authors, from the department of neurology at the University of Auckland, wrote: "Nitrous oxide is not routinely included in drug education programmes
"Generally, few students were aware of the potential acute or chronic ill effects from use of this substance."
A spokesman for UK charity Drugscope said that nitrous oxide use was not illegal in the UK.
He said: "I wouldn't claim it was a particularly harmful drug - but I wouldn't say it was completely without harm as well.
"No drugs are harmless."
There is, however, a history of the popularity of nitrous oxide use in the UK.
In Victorian times, the use of this, and other anaesthetic gases, was a popular pastime.
Many medical students down the years have also sampled it, owing to ease of access to the drug in a hospital setting.