There are fears there is a new chemical or poison in a drug that's been linked to a spate of deaths in Auckland this month.
Police and the chief coroner yesterday issued an urgent warning after seven people who had used synthetic cannabis recently, or were found with the drug on them, died.
Ross Bell, the Drug Foundation's chief executive, said synthetic cannabis had been in New Zealand for a decade, but there had never been a group of deaths like this.
He said that raised questions about what exactly was in the drug and whether there was a poison, opioid or other chemical in it.
"It can't be one of the chemicals that we've had in the last 10 years because we haven't simply had this experience before, my fear is we're dealing with something new."
Mr Bell said better information needed to be made public about what chemicals had been found in any blood or forensic testing, what people should be looking out for and how medical staff should respond.
He was also concerned that the deaths appeared to be confined to Auckland.
"It could well be that it is a bad batch that is doing the rounds, or it is a new chemical that's doing the rounds, or it's a new poison that happens to be available in Auckland, because we haven't seen deaths like this in other parts of the country."
The sale and supply of synthetic cannabis products was banned in 2013.
Labour leader Andrew Little said Parliament should take another look at those law changes, with the involvement of health experts and others.