Counterfeit Xanax pills laced with a powerful painkiller have become a party drug among some young people. Now Public Health England is warning users they are "dicing with death".
"I was at a party when a friend shared it with me," says Kristello, a 19-year-old rapper from Birmingham, remembering the first time he took Xanax.
The drug, also known by the name Alprazolam, is widely prescribed in the US to treat anxiety and can be obtained on private prescription in the UK.
But among some teenagers and young adults in the UK it has become a popular recreational drug used illegally.
Kristello - who wished to go by his rap name - says his addiction soon grew into a daily habit as he began taking one tablet a night.
"The high felt like it was very floaty, and any worries you had melted away," he tells the BBC's Victoria Derbyshire programme.
"But what you have to take into consideration is what happens after you take Xanax, which is where the problem really starts."
Nine months ago, after deciding to come off the drug, Kristello struggled sleeping at night and experienced wrenching stomach pains, cold sweats and extreme paranoia.
"It can be really bad on your mental health," he says.
"You can experience blackout with memory loss. Your long-term memory can be affected as well."
Xanax has previously been glorified by hip hop artists, and is often featured in lyrics.
In November 2017, the rapper Lil Peep was found dead after an overdose of Xanax mixed with fentanyl - a powerful synthetic painkiller.
It is a lethal combination which, officials say, users risk being repeated when buying counterfeit Xanax online and through street dealers - because they cannot be sure how the drug has been mixed.
According to National Crime Agency (NCA) figures, 113 people have died using fentanyl in the last 12 months in the UK.
"The danger we've got here is young people who are used to taking the drug [Xanax] who think they know what they are doing," says Tony Saggers, former head of drugs threat at the NCA.
"The great disaster is when these tablets are supplied between friends, and one friend kills another friend because they've sold them something without knowing what it was."
"These are two Xanax bars. I spent £5 for both," says 18-year-old "Kieran" - not his real name.
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About twice a month, on a Friday or Saturday night, Kieran and his friends gather for a Xanax "drug party" at his one-bedroom flat in Dudley.
There are 12 people milling around in his living room. Some are playing PlayStation, drinking alcohol - others are mixing Xanax with other illegal drugs.
"The best way to describe it is you feel like a marshmallow. It's a very chilled drug," says Kieran's friend "Jordan", also aged 18.
Jordan and Kieran - who say they have unintentionally taken counterfeit Xanax spiked with fentanyl in the past - swallow the tiny white pills with alcohol, which makes it even more dangerous.
"I feel really, like, drowsy. I feel a lot like a cloud. I just feel comfortable," says Jordan 20 minutes later.
When challenged about the potential dangers they are exposing themselves to, both say they are aware of the risks but choose to take it anyway.
"I guess sometimes we see past [the warnings], we don't really think about it. We see on the media people passing away but it doesn't seem to faze anyone really."
'Dicing with death'
Experts say that, despite the warnings, the use of counterfeit Xanax appears to be growing, though there are no figures available to know exactly how widespread its use is.
"It is a real and immediate concern among the young people who it seems to be a drug of choice for," says Rosanna O'Connor, Public Health England's head of alcohol, drugs and tobacco.
"People buy things from the internet and they have no guarantee of what they are getting so whatever is in the drugs they buy could change from one drug to another, so they are dicing with death really because these things are dangerous."
Pfizer, the company that developed Xanax as a prescription drug, said it was "alarmed" by the rise of counterfeit versions of Xanax that, it said, have been found to contain acid, heavy metals and even floor polish.
A government spokesman said it was "taking coordinated action to tackle illegal drug use alongside other criminal activity.
"Law enforcement agencies continue to work with internet providers to shut down UK-based websites found to be selling prescription-only medicines illegally.
"Prescription-only medicines are potent and should only be prescribed by a doctor or appropriate healthcare professional."
Anne McDermott, from Edinburgh, knows all too well the extreme risks associated with the drug.
Her son Scott died aged 34 when she says he took Xanax.
She believes the substance - which has been linked to a number of deaths across Scotland's capital - is responsible for killing her son in January.
"The first time he took Xanax he was completely out of it. He went back the next day, the next day and the following day, and that's what happened.
"It was an extremely powerful, potent drug."
Watch the BBC's Victoria Derbyshire programme on weekdays between 09:00 and 11:00 on BBC Two and the BBC News Channel.