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.
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Wednesday, May 04, 2016 3:46:00 PM