Go to any nightclub and, if you know what to look for, you will see people on ketamine. You can spot them because, unlike those who have taken ecstasy or cocaine, they stand nearly motionless, struggling to move. They appear lost in a self-inflicted paralysis. This is called a ‘K-hole’– a state induced when ketamine is taken in large doses, causing a person to slip into a dissociative state. It can be terrifying: they are temporarily unable to interact, and even move. Users feel separated from their body and reality. Time is grossly distorted: hours passing can feel like a few minutes. Anyone who works in A&E will see people in K-holes regularly.

This horse tranquilliser, half the price of cocaine, has become the go-to party drug

A few months ago, I was at a relatively sedate and middle-class house party. When I went to leave the host asked me to help with two guests who weren’t moving. In a bedroom two people in their mid-twenties were lying on the bed motionless, awake but un-able to communicate. One was on his back and choking on his tongue. They’d both fallen into K-holes.

Despite the pitfalls of the K-hole, the drug (which is snorted) has become wildly popular, particularly among middle-class Gen Zers. The number of 16- to 24-year-olds who have tried ketamine has hit 6 per cent, treble the rate 15 years ago. Ketamine, K, ket, special K, donkey dust, whatever you call it, this horse tranquilliser has become the go-to party drug. It’s half the price of cocaine; a bag is cheaper than a round of drinks. It accounts for a quarter of all drug seizures at music festivals in the UK. But if dosed right, it can bring on euphoria and states of extreme relaxation.

The downsides are grim. A single dose can kill, especially if mixed with other drugs or alcohol. Matthew Perry died in October from the ‘acute effects of ketamine’ and drowning – he was found in his hot tub. He had been prescribed therapeutic ketamine infusions for depression, but the ketamine found in his system could not have been from this, as it was last given more than a week before he died. The lethal effects of the high levels found in his blood would, according to the post-mortem report, be from cardiovascular overstimulation and respiratory depression. Even for a self-confessed seasoned drug user like Perry, taking ketamine is walking a tightrope: one slip can be fatal. Some 41 students in the UK died last year with ketamine in their systems, according to the Times.

As with many drugs, the problems are exacerbated by users building up a tolerance, meaning they need ever-larger quantities to get the same effect. This makes it easier for them to misjudge and overdose. Then there’s the danger that drug dealers have cut it with other substances; users never quite know what they’re taking.

Ketamine can cause severe, sometimes catastrophic, bladder problems. It’s estimated that around one in five users experience some kind of troublesome urinary symptoms. Some studies say the numbers are even higher: one Spanish study found it was nearly half of all users; another in Hong Kong found it was nine in ten. These bladder problems include ulcerative cystitis and contracted bladder. Open sores inside the bladder cause severe abdominal pain, blood in the urine and frequent, desperate trips to the toilet.

Ketamine can make bladders permanently shrink in size to that of a toddler. The damage can be agonising and catastrophic. I’ve seen two patients who have attempted suicide because of it. Tragically many users resort to using ketamine more to cope with the pain, creating a vicious cycle. The NHS body for urology surgeons is so alarmed by the rising cases of ‘ketamine bladder’ appearing that it is preparing nationwide advice (a ‘consensus document’) for doctors on how to identify and treat the condition.

Then there’s the damage that it does to brains. Ketamine abuse has profound and long-term effects on memory and cognition. One three-year longitudinal study found that, while some aspects of memory impairment improved when users stopped taking the drug, other aspects of memory remained impaired, as did attention. Schizotypal symptoms (peculiar thoughts, paranoia and perceptual disturbances and distortion) persisted. The study concluded users should be aware of the enduring effects of ketamine on memory and subjective experience.

These dangers have had very little cut-through. Everyone knows cocaine is bad for your heart; that alcohol damages the liver. But when I mention to friends or patients the need to be careful about ketamine, they are sceptic. Younger patients will often look at you in horror if you ask about ‘hard’ drugs like cocaine or heroin. ‘Oh no,’ they reply, ‘I’d never do anything like that, just a bit of ket on the weekends.’ Even when someone is in a K-hole, the general attitude from other users is: ‘Oh don’t worry, they’ll come out of it soon.’ In reality they are dangerously close to death.

Ketamine has managed to escape without many of the scare stories that are attached to other drugs. The laissez-faire attitude to it is, in part, because its ubiquity is relatively new so it has avoided the headlines other drugs have attracted. While it’s been around for more than 50 years, it has only been used recreationally since the 1980s. Even then, it was a niche, underground drug mainly used by hardcore clubbers. It’s only in the past decade or so that it has gone mainstream. When I was at university 25 years ago, I never even heard of anyone taking ketamine; now it’s the drug of choice on campuses.

There’s increasing interest in its use as an antidepressant and as an aid for wellness and mental health. This latter use has been excellent PR for ketamine: it has made it socially acceptable, a sort of alternative to Big Pharma antidepressants. It’s very much ‘on brand’ for Gen Z. Its use in depression is still very much in its infancy, though, and is a world away from drunkenly snorting it off a key in a nightclub toilet. In any case, the use of ketamine – which was first given to humans for medicinal purposes during the Vietnam war – to treat depression is strictly controlled and carefully monitored. (Curiously, Ukraine – where ketamine has been legal to treat mental health issues for seven years – is currently pioneering ketamine psychotherapy for its soldiers.)

The fact that it is only a class B drug has contributed to its popularity boom. Other drugs such as cocaine, heroin and ecstasy are class A. This helps give legitimacy to the idea that it isn’t really that dangerous. It also means that it has become the drug dealer’s drug of choice, because selling it carries less harsh sentences than other drugs.

Ten years ago ketamine was reclassified as class B from class C. There are now hints it could be upgraded again. Late last year, the Home Office minister Chris Philp suggested that the government is open to reclassifying the drug. In a letter sent to the Tory MP Craig Tracey, who had written to Philp after he had a constituent who died from ketamine abuse, Philp replied that the Home Office is open to changing its status. ‘If you have evidence that there are systemic harms caused by ketamine on a widespread scale, which may mean reconsideration of the classification from class B to class A is merited, then please do share this with the Home Office,’ he wrote, ‘and I will make sure that it is considered very carefully.’

There is of course a bigger issue about whether the war on drugs can be won, or indeed if a war was ever really started, given the lenient sentences that are dished out and the turning of a blind eye by police towards some drug use. But that’s a piece for another day. The reality in the here and now is that ketamine usage is rising to dangerous levels and Britain is woefully behind in addressing the issue. For as long as it remains a class B drug, ketamine will continue to destroy lives. Let’s hope Mr Philp really does consider its dangers ‘very carefully’.