Synthetic marijuana is catching on huge right now in UK prisons and causing a rash of health problems and erratic violence among inmates. Spice – the same trashy chemically-sprayed shake sold in some US head shops – is the most common brand you’ll see in a UK prison, but whatever the brand inmates call it “Black Mamba.”

An inmate told VICE, “It’s all about Mamba inside now, and it’s sending people mad. But it sends people mad in different ways—unlike weed, coke, or heroin, which you know how you’re gonna act or how a brother will be high, this stuff is nuts.”

He added, “People look straight through you, then head butt a wall or try to fight you or officers, then the next day they have no idea what they’ve done. There’s a saying in the nick: ‘If you’re gonna smoke the Mamba, you better phone the mambulance.’ And it’s true—after a few pulls I was convulsing on the floor. And the whole wing knows, too, so the cheers go up when the mambulance comes.”

“Mambulance” is a common term in the culture. It means getting medical treatment after overdosing on black mamba.

Part of the reason for the drug’s skyrocket in popularity is that it is untraceable in urine tests. Inmates use it for recreation, but also to manipulate newcomers to the prison. They’ll oftentimes pressure newbies into overdosing on mamba and watch them go crazy for amusement, or get a new inmate so fucked up they don’t know what’s what, then take their possessions.

Mamba is cited as the number one problem in UK prisons right now by the UK Prison Officers Association and Parliament reports have shown a steep increase in assault and self-harm since the rise in mamba use.

Prison health care workers and ambulance crews are being trained to treat the array of unpredictable problems a mamba OD can cause, among them: hallucinations, acute psychosis, incontinence, hypertension, blurred vision, and epileptic fits. It can cause instant depressive or comatose states or extreme paranoia and anxiety, depending on the individual.