Forensic analysis has revealed that other recently seized pills have been found to contain the highly toxic chemicals PMA and PMMA as well as ecstasy, police confirmed on Wednesday.
"Despite previous warnings by police and continued uncertainty surrounding the causes of a number of recent unexplained deaths, people are continuing to put their lives at risk," Detective Inspector Andy Dunlop of the PSNI's Organised Crime Branch said.
"The combination of MDMA (ecstasy) and PMA can be particularly hazardous to health and has been linked with numerous deaths world-wide.
"PMMA (paramethoxymethamphetamine) is particularly toxic. Both dealers and users may be unaware that what they believe to be ecstasy actually contains PMMA.
"PMMA pills are slower to take effect. This may cause the user to take more - which can lead to seizures, convulsions, heart attack and ultimately death."
Police are urging the public to be wary if offered green-coloured tablets bearing a Rolex-style crown logo.
They also advised against taking controlled drugs, improper use of prescription medication and not to mix either with alcohol.
DI Dunlop added: "There is no such thing as a safe drug or a safe dose. We do not want people to think that all other drugs are safe. This is clearly not the case.
"These chemicals have also been found in numerous other coloured pills bearing different logos throughout Great Britain, Europe and in Canada.
"They have been directly linked to death. Anyone found suffering ill-effects after having taken drugs should be treated as a medical emergency."
Police are investigating the sudden deaths of eight people in their 20s and 30s in Belfast and Co Londonderry in recent weeks.
Health authorities said there was no single drug link but the PSNI are still awaiting the results of forensic tests to establish if other drugs were involved.
They have asked anyone who is aware of anyone involved in the supply of controlled drugs to contact their local police.