Ecstasy and MDMA is getting stronger with dangerously "pure" pills and crystals in circulation, it's claimed.
There's a new warning from the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA).
Its latest report highlights a "recent resurgence in use of MDMA in Europe and increased availability of high-strength MDMA tablets and powders".
At the weekend a 17-year-old girl thought to have taken ecstasy died after a rave in Manchester.
Faye Allen from Liverpool is thought to have had an adverse reaction to a strong form of the drug, nicknamed "Mastercard".
It's thought the pills are very strong and have a line across them because they're designed to be snapped in two.
Harry Shapiro is editor of Drugwise, an online drug information service.
"It seems a bit perverse to make an extra strong batch of ecstasy tablets that you can break in half deliberately," he tells Newsbeat.
"Ask the question of the underground chemist - do you really need to be making pills at that strength?"
He's urging people to avoid the drug completely.
"If people are determined to take ecstasy, in whatever form, they shouldn't be taking all of it all at once.
"They should be breaking these things up, whatever strength they are."
The new report says the resurgence in dance music culture could be connected to a rise in use.
"This global commercial success of EDM provides a huge and fertile ground for the distribution of MDMA among a new generation of young consumers who were born after the 1990s clubbing and 'ecstasy' events."
Harry Shapiro agrees it's a factor and says the report by the EMCDDA is right to claim that ecstasy tablets and MDMA are getting more potent.
"There has definitely been stronger ecstasy on [UK] streets than we have seen in previous years," he told Newsbeat.
"The average dose is around 75 to 100 milligrams per pill, but there has been ecstasy on the streets that has been double that and more.
"The powder and crystals can be stronger than the tablets too.
"That's also combined with a new generation of users not exposed to the harm messages of the eighties and early nineties."
Shapiro also warns that people need to get reliable drug advice and education.
"There is a bit of mythology that drugs cut with other things are more dangerous than the pure drug - and that as far as ecstasy is really not the case."
There is BBC Advice here on ecstasy and MDMA.
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