Police believe the deaths of three men in Suffolk are linked to a "dangerous batch of drugs" which appeared in the Netherlands last month.
The pills, believed to be red and triangular with an "S" Superman emblem, had a large concentration of PMMA, which acts more slowly than MDMA.
This can encourage people to take more pills as they do not think it is having an effect.
PMMA can cause a high body temperature and an increased heart rate.
A spokesman for Suffolk Police said this is the first time they have come across pills matching this description.
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