Police say the two men in Wigan who died from suspected contaminated ecstasy had taken four or five tablets each.
The two men who died after taking what police believe were contaminated ecstacy pills have been named as Jordan Chambers and Gareth Ashton.
Jordan, 19, died at the Royal Oldham Hospital on Sunday.
The following day police were also called to the Wigan Infirmary after 28-year-old Gareth died.
Police are investigating whether a contaminated batch of ecstasy has caused the deaths of two young men.
A 19-year-old man died at Oldham hospital on Sunday and a 28-year-old man died at Wigan Infirmary yesterday after suffering similar conditions.
Over the last few days it is believed a number of other people may have been admitted to hospital suffering from similar symptoms.
Toxicology results have not yet taken place but detectives are investigating the possibility that they died after taking contaminated pills.
They are now warning drug users about the tablets, believed to be heart shaped and purple, green, yellow and blue.
Detective Chief Inspector Howard Millington from Wigan CID said: “We are very concerned at how these deaths of two apparently fit young men have occurred.
“It is believed several other people have been admitted to hospital suffering from similar symptoms.
“It is possible that they are linked and this is something we are exploring as part of the investigation.
“Our main concern is that there may be a contaminated quantity of illegal drugs and if this goes unchecked it could result in further deaths.
“The drugs are believed to be ecstasy tablets, heart shaped in purple, green, yellow and blue.
“If you are suffering adverse effects after taking one of these tablets I would advise you to go to hospital for a check up.
“If you have any information, I would ask you to contact police as soon as possible. We will treat the details you supply with the strictest of confidence.
“I would always urge people not to take illegal drugs and remind them that you do not know what they have been made up with.
They can contain poisons and illicit chemicals that can have potentially fatal effects.”
Anyone with information should phone police on 0161 856 7149 or the independent charity Crimestoppers, anonymously, on 0800 555 111.