Children as young as 13 are getting ketamine bladder damage, doctors running the UK's first and only dedicated NHS clinic for it have told the BBC in an exclusive interview.
Medics at Alder Hey Hospital in Liverpool say some patients - they have had over 100 referrals since opening last May - describe 'peeing a jellyfish', which is some of the bladder's protective lining being shed.
Prolonged damage can lead to incontinence or uncontrolled peeing, and even kidney failure.
Many children at the clinic had been taking ketamine for a year or more, meaning some may have started when they were 12 or younger.
Some with emotional trauma say the ketamine, sold for pocket money prices, helps "shush" or quieten their brain.
The drug is a general anaesthetic so it reduces or blunts sensations in the body.
Users say it can make them feel dream-like and detached, chilled and relaxed.
But it can also cause extreme harm.
Prof Rachel Isba who runs the clinic told the BBC some of the children she has seen had started wetting the bed or having to go to the toilet more often and in a hurry.
"Sometimes they don't always make it. They might have accidents...and a lot of them report pain in their bladder.
"They describe this feeling of weeing over broken glass. It's very painful."
She says, unfortunately, some of them will use the ketamine to treat the pain.
"Ketamine is a very good pain reliever. It's an anaesthetic, and so they get into a vicious cycle or 'K loop', which makes their bladder worse," says Isba.
She says ketamine is very cheap, "pocket-money level".
"And you only need a small amount to feel an effect."
She says some children find it hard to quit if their mates are still doing it.
"There's use going on at school. That's really difficult. And, unfortunately for many of these children they are not able to attend education for various reasons."
Some had pre-existing conditions like ADHD, while others had been in and out of the care system.
Ketamine abuse in children and young people is on the rise in the UK.
The Alder Hey doctors saw one young patient in 2023, nine in 2024, and then "a rapid escalation" in 2025, which led them to open the bespoke clinic in May.
They get about one referral every week from GPs or emergency departments in Cheshire, Merseyside and other nearby regions.
Of the first 60 they saw, 43 were girls.
Despite its name, "ketamine bladder" can affect the entire urinary tract, including the kidneys and ureters.
Symptoms include an urgent and frequent need to urinate. This can be very painful and the pee can be blood-stained.
Although stopping using ketamine can help, sometimes the damage can be so serious that the bladder needs surgical repair or even removal.
Some users experience abdominal pain and spasms, or "K cramps" too.
There are reports that heavy users are getting liver damage, but it is difficult to separate harms from other things people may also be taking, including other street drugs and alcohol.
Isba says cannabis and alcohol are still more popular, but ketamine is "probably up into third place".
Children at the clinic often say they have also tried other drugs, drank alcohol, and vaped.
About three out of every 10 people who frequently use ketamine get bladder issues, says the British Association of Urological Surgeons.
Sometimes it is reversible, if the drug use stops.
Given the risks, there have been calls to reclassify it as a Class A drug - like cocaine and heroin - but the Advisory Council on the Misuse of Drugs has recommended to government that ketamine should remain a Class B controlled substance, like amphetamines and cannabis.
Isba says children are disadvantaged when it comes to accessing services.
"There are definitely some children out there who are under the age of 16 who if they were 18 would be offered an inpatient detox stay. But because we don't have those facilities in the UK, they are not able to access that and that feels unfair. Particularly for the ones who are ready to stop."
