Police now believe that the 26-year-old man from Rochdale took a crystallised and unrefined version of the drug Spice.
Ch Supt Neil Evans, described the development as "extremely worrying".
Ten people were admitted to hospital after taking the drug over the weekend, with four kept in intensive care.
A police spokesman said they were hospitalised after taking what was thought to be a new form of MDMA, known as "pink champagne".
But he added: "It is now believed that this substance was in fact a synthetic cannabinoid, like 'Spice', however it was sold as MDMA."
Ch Supt Neil Evans said: "This is the first time we have seen 'Spice' in crystallised, and much more potent and unrefined form and it's now being mistakenly taken as MDMA."
He added: "Anyone thinking of taking MDMA must seriously consider what they are doing.
"You may feel that you know and accept the risks of taking MDMA, but you never know what you are actually taking and the reaction your body could have to it."
A 26-year-old man, held on suspicion of supplying Class A drugs, was released while inquiries continue.
A man thought to have been killed by the drug MDMA had taken a "much more potent version" of Spice, Greater Manchester Police has said.