The dangerous chemical AMB-FUBINACA, linked to seizures and other adverse medical problems, has been found in synthetic cannabis recently linked to the deaths of up to 20 people.
On Thursday, police and Chief Coroner Judge Deborah Marshall repeated their warnings to the public about the dangers of using synthetic drugs.
It comes following the recent deaths of two men aged 22 and 37, and a 26-year-old woman, all from West Auckland, in separate incidents and where the Coroner is investigating whether synthetic drugs were a possible cause of death.
A 21-year-old man in Feilding also died from possible synthetic cannabis use recently.
The Office of the Chief Coroner has around 20 cases under review.
Detective Inspector Scott Beard says the dangerous chemical AMB-FUBINACA has been found in most of the synthetics being lab tested.
"I want to be very clear that we have been open and transparent about our testing - this is what ESR is finding in the drugs we have seized," he said.
"It is a dangerous drug that we know is a synthetic compound usually manufactured overseas.
"Those taking it are taking a huge risk because you do not know where it has come from, or the level of dosage."
AMB-FUBINACA was developed by pharmaceutical company Pfizer, but later abandoned. It has been sold online as a designer drug.
In July 2016, more than 30 people were hospitalised in zombie-like states in Brooklyn, New York, after taking it.
It was banned in Louisiana in 2014 after it was linked to people suffering seizures.
Judge Marshall said each case before her involving synthetic cannabis is a tragedy and urged anyone thinking of trying it to not do so.
Det Insp Beard, meanwhile, urged the community to tell police who is selling and manufacturing these drugs.