A man woke up unable to walk. It turned out vitamin B12 was inactivated in his body after he took laughing gas.

• When Vito Oliveri, 34, and Emily Shuford, 30, first used nitrous oxide they felt instant euphoria.

• Eight years after first using the drug, Oliveri got pins and needles and woke up unable to walk.

• Experts are worried about nitrous oxide's potential harms amid the rise of super-size canisters.

When Vito Oliveri first tried nitrous oxide in his twenties he didn't expect a legal drug that gives a quick high to temporarily paralyze him and his fiancée years later, leaving them unable to walk their four dogs.

As recently as early last year, Oliveri, 34, who lives in Portland, Oregon, near some of the best ski resorts in the US, would often ski or take trips to the lakes with his fiancée, Emily Shuford, 30.

"I'd typically be on the mountain on a Monday like today, but we just can't. Emily uses a cane and I probably can't walk a mile. We've been limited to the house, probably since April of last year," Oliveri told Insider in February.

Nitrous oxide, also called "laughing gas" or "hippie crack," is used as a painkiller during labor and for whipping cream in catering. But it's grown in popularity as a recreational drug in the US, Australia, and Europe in recent years, with people inhaling it for a relaxed, giggly, euphoria that lasts, on average, one to two minutes.

Experts have become increasingly concerned about nitrous oxide and its potential harms, particularly amid the rise of super-size stainless steel canisters, which came onto the market in around 2017 to "deliberately target" recreational users, according to a recent European Monitoring Centre for Drugs and Drug Addiction report.

"Maybe once every five or six years, I'll see a patient who's had a stroke from taking cocaine. Yet, every week, I'm seeing this in my ward. So from my point of view, this is actually a bigger problem," Dr. David Nicholl, a consultant neurologist at Sandwell and West Birmingham NHS Trust, UK, told Sky News on March 1.

When Oliveri first took the drug, he attached a silver lipstick-sized capsule containing 0.2 ounces of nitrous oxide to a whipped cream dispenser and filled up a balloon that he inhaled the gas from. He liked it right away.

Oliveri said that while the "little crackers" can taste bad, the bigger cylinders are more convenient, tasteless, and produce stronger euphoric effects.

Laughing gas can inactivate vitamin B12 in the body

Nitrous oxide can paralyze people because it destroys nerve cells within the spinal cord by inactivating vitamin B12, which is essential for maintaining the lining of the nerves, Alistair Noyce, a consultant neurologist working in a London hospital in the UK, told Insider.

That nerve damage can also cause tingling and numbness of the affected body part, with the severity of symptoms depending on how extensive the damage is, according to Noyce, who is also a professor at the Preventive Neurology Unit at the Wilson Institute of Population Health, Queen Mary, University of London.

People can also lose their balance because signals that tell the brain where body parts are positioned don't get transmitted properly, Noyce.

Oliveri, who has trouble balancing from the nerve damage caused by nitrous oxide, falls over when his dogs jump on him or pull their leash. He now sends two of his dogs — a chocolate Labrador and German Shepherd — to doggy daycare once a week so they get enough exercise.

Oliveri shared his story to raise awareness of the dangers of using nitrous oxide.

"There's a warning on alcohol bottles, there's a warning on cigarettes that tell you what's going to happen but for nitrous oxide, there's nothing," Oliveri said.

A doctor has seen people in their teens and twenties disabled by nitrous oxide

It's legal to possess nitrous oxide in most countries, but some have criminalized supplying it for recreational purposes.

The Netherlands recently banned its possession and sale over concerns about nerve damage and traffic accidents from people driving high, and the UK, where its illegal to sell but not to possess, could soon follow.

In the US, New York state banned its sale in 2021, partly because of the risk of abuse, and in California recreational use is a misdemeanor.

While it's rare for people who don't use the drug often or in low quantities to get nerve damage, Noyce said he'd seen patients experience it after one use but he doesn't know if those cases happened at random or if they were susceptible for some reason.

Noyce said he'd seen people, mostly in their teens and twenties, at the hospital who were "really very disabled" from using high quantities of nitrous oxide, needing to use a walking frame or wheelchair, and others who were incontinent or unable to get an erection.

Noyce said that there isn't an agreed definition of "heavy use," but a ballpark figure is using more than 10 to 15 canisters more than once a week, citing his own research, while the Dutch Poison Centre classes puts it at inhaling 50 or more balloons in a single session.

Users who develop symptoms like numbness, unexplained incontinence or problems with erections should stop taking it, immediately seek help, and tell a doctor that they use the drug because prompt treatment with vitamin B12 injections is "crucial," Noyce said.

"Some recover, some don't," he said.

Super-size cylinders are easier to use but more dangerous

Oliveri first tried the drug when he was 26 years old, partying with co-workers on a cannabis farm in California, before he met Shuford.