There's a warning cocaine in the UK is getting stronger - and more users are ending up in hospital.

Drug testing services, a former police drugs chief and regular cocaine users all tell Newsbeat it's getting more potent.

This is backed up by data from the Global Drug Survey (GDS), the largest poll of its kind in the world.

It claims the percentage of UK users being sent to A&E after taking the drug has doubled in the past three years.

Josie, whose name we've changed, agrees to meet us in a cocktail bar.

"I've noticed it getting stronger maybe since the beginning of this year," she says.

She and her friends buy cocaine whenever they can afford to, usually for "special occasions".

"I've heard more horror stories too. A friend was out at a club where someone took coke that was nearly 100% pure and they died.

"I must admit more recently I've been more worried, but when you're in the moment and you've got it and paid for it you just kind of ignore the worries."

It's a picture that's mirrored in the drugs that are being seized from the street, too.

Earlier this month police in East Sussex blamed two deaths on super-strength cocaine.

"Certainly talking to my colleagues in the UK in law enforcement, I think over the last three or four years it's become a regular pattern," Paul Bunt tells Newsbeat.

He spent a decade in charge of drug strategy at Avon and Somerset Police and now advises music festivals like Glastonbury and Boomtown.

"Purity has traditionally been around 20%. It's now an established thing that we do have higher purity cocaine - 40, 60 and even 80% - regularly available on the street."

Dr Adam Winstock, who runs the Global Drug Survey, thinks it's got to the stage where it's causing problems.

The GDS asks drug users about their experiences. This year it's had more than 120,000 responses online.

"Every year we ask people, 'Have you ended up in the A&E department?'" Dr Winstock explains.

"Over the last three years the proportion of people in the UK seeking emergency medical treatment has doubled from 0.5% to 1%.

"They turn up at A&E with panic, anxiety, chest pain. They can't breathe, they're too sweaty, they're agitated. All of the things you would expect when someone's taken too much coke."

There's no simple answer as to why purity is rising, but the availability of drugs online is thought to be partly behind it.

Much like on legal websites, market places on the dark web allow people to leave reviews of the drugs they've bought.

This gives dealers an incentive to make sure their product is as pure as possible.

"Seven per cent of the cocaine users we spoke to said the last time they bought coke they bought it on the dark net," Dr Winstock says.

"And of course that's becoming an increasingly attractive way of people buying drugs without getting involved with gangs and violence."

But Fiona Measham, a criminology professor at Durham University who runs a drug testing service called The Loop, thinks there are plenty of other reasons.

"What's quite significant is that we've had a cut in policing. There are 20,000 fewer officers in the UK and I think this means there's less of a focus on enforcing drug laws.

"I think there have been changes too in the way borders are policed and there's been a focus on illegal immigrants and on terrorism.

"There was a squeeze around 2008 in terms of drugs being taken into the UK, but I think cuts in public services have had a big effect."

For help and support on cocaine use, check these BBC Advice pages.

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