A girl in her 20s struggles to walk. She has nerve damage to her spinal cord and may never recover.

What is a 'nang'? A "nang" is the street name given to a small canister of nitrous oxide, or laughing gas

A "nang" is the street name given to a small canister of nitrous oxide, or laughing gas It is available over the counter, and has various uses including in medicine and hospitality

It is available over the counter, and has various uses including in medicine and hospitality However, selling it for non-medical human consumption is illegal in NSW

However, selling it for non-medical human consumption is illegal in NSW It can cause brain damage, memory loss, a weakened immune system and incontinence

The cause? Bingeing on "nangs" — small canisters of nitrous oxide gas designed for whipping cream, but being misused as a recreational drug.

The female student was inhaling 360 nangs a week. Her future is bleak.

Partygoers buy nangs (also known as nozzies, bulbs and whippets) to inhale the nitrous oxide inside the canister. It is a 20-second high.

In a medical setting, nitrous oxide is useful. Dentists use it as an anaesthetic and it is administered to women in labour.

But doctors warn recreational use carries serious risks.

"Very recently I had a 20-year-old patient whose brain appeared to have the same level of damage as an alcoholic who had been drinking for 40 years," toxicologist Dr Andrew Dawson told 7.30.

Dr Dawson, who is Director of the Poisons Information Centre at The Children's Hospital at Westmead, said the number of cases had risen alarmingly.

"We have had a doubling of the number of calls from hospitals about significantly affected people from nitrous oxide exposure," he said.

"Those effects are severe nerve injury, or sometimes brain injury.

"There has been a real spike over the last two years."

Although deaths are rare, Dr Dawson said they were "certainly" reported within Australia.

"Those deaths can relate to anything from the exploding of the small cylinders, to people becoming hypoxic — that is, short of oxygen, from overuse," Dr Dawson said.

Coronial statistics back that up.

Since 2010 there have been two recorded deaths from recreational nitrous oxide use in Australia.

Sorry, this video has expired Doctors warn of dangerous rise in use of 'nangs'

24/7 delivery: Why 'nangs' are on the rise

Nitrous oxide, also known as laughing gas, has been around for hundreds of years.

It has been used to get high for just about as long, beginning with the British upper class "laughing gas parties" in the 1700s.

Now it is back with a vengeance.

According to the Global Drug Survey, nitrous oxide is the seventh-most popular drug in the world.

In Australia, canisters are sold in packs of 10 for $10 in corner stores, or in bulk online, with multiple sellers advertising 24/7 weekend delivery.

Maighan Brandwood, 21, regularly shares a couple of boxes of with her mates on weekends, and compares the delivery services to UberEats.

Maighan Brandwood and her friends often use nangs on the weekend. ( Supplied: Maighan Brandwood )

"You can go on these websites and order them," Ms Brandwood told 7.30.

"Someone just rocks up to your house on a bicycle and opens the backpack up, and there you go."

That is exactly what is worrying experts, including the fead of Clinical Toxicology at Prince of Wales Hospital, Dr Betty Chan.

"We have noticed, through the Poisons Centre, there is an increased volume of inquiries about exposures and side-effects," she said.

The situation has prompted doctors, including Dr Dawson, to call for the supply of nitrous oxide to be limited, and a public health education campaign to warn about the risks.

"Kids are intelligent," Dr Dawson said.

"It is an issue about actually getting that message across in an appropriate manner.

"Those people who are actually providing those companies with large quantities of nitrous … have to take some responsibility and look hard at where things are being distributed."

Who's doing it? International students targeted

A festival-goer inhaling nitrous oxide through a balloon ( Reuters )

International students are a big market for nang retailers, with some using services like WeChat to target Chinese students.

According to Dr Chan, they are an easy target because they do not have parental supervision and have a disposable income.

"Because of its easy availability, we notice that it has become an issue amongst those international students," she said.

It is not hard to find a university student in Sydney who is knowledgeable about the drug.

Shaza Smit does not do nangs herself, but plenty of her friends do.

She said its use was "absolutely" on the rise.

"I wouldn't even say that it is limited to student life," she told 7.30.

"I think it's definitely feeling its way into corporate [life] as well."

Is it legal?

The law on nitrous oxide varies from state to state.

A box full of empty nitrous oxide canister, or nangs

Across Australia, the sale of nitrous oxide canisters to whip cream is legal.

However, some states and territories, including NSW, Victoria, South Australia and the Northern Territory, have made it an offence to supply them to anyone who they believe intends to misuse them.

"I think they definitely know that their service is for partygoers," Ms Brandwood said.

"Especially when you open the door and you have a balloon in your mouth!

"I don't think they think you are making a cake at 3:00am."

According to Dr Dawson, retailers are breaching the "spirit" of the law.

"The intent of the act is that it shouldn't be sold in quantities that could be abused — but how that is policed is actually probably very, very difficult," he said.

The NSW Drug Squad Commander, Detective Superintendent Tony Cooke, said police were concerned about the use of nitrous oxide.

"There is plenty of information out there about the dangers of the use of nitrous oxide — with side-effects that include sudden death," he said.

"To suggest it might be OK to inhale gas from a cream whippet or bulb is worse than naive — it's flat-out stupid."