Provisional figures from the coroner show that more than 70 people have died from synthetic cannabis toxicity in the past two years.

Chief Coroner Judge Deborah Marshall said 24 people had died as a result of synthetic cannabis since June 2017, and there were 50 other cases where synthetic cannabis toxicity appeared to be the cause of death - a total of 70-75 deaths.

"There are also a number of deaths where while synthetic cannabis contributed to the death, synthetic cannabis toxicity was not the ultimate cause of death," Judge Marshall said.

A coroner's report released today into the death of Joseph Rakete on Queen Street in 2017 found he had a lethal mix of cannabis, synthetic cannabinoid, methamphetamine and alcohol in his system.

Coroner Judge Debra Bell noted the consumption of synthetic cannabis was a serious factor in Mr Rakete's death.

Dr Paul Quigley from Wellington Hospital's emergency department said synthetic cannabis was the deadliest recreational drug the country had ever seen.

"When they take even just their first couple of breaths, usually from a bong, they initially become paralysed and then they go into this zombie phase," he said.

"For some victims, if they've got a cardiac condition, or in combination with some of their normal medications, their heart can go into a fatal rhythm."

He said at one point the drug appearing in New Zealand was fifteen times stronger than that being sold in New York.

Dr Quigley said synthetic cannabis was much cheaper than natural cannabis and was highly addictive.

Psychologists were finding it hard to treat addicts because patients craved the drug for months after giving up.

In addition, many had ongoing psychological side-affects including hallucinations and delusions.

Drug Foundation executive director Ross Bell said the drug's potency was only part of the problem.

Those addicted to synthetic cannabis often came from vulnerable situations, were homeless and used multiple substances.

Mr Bell said the synthetic cannabis crisis should have been addressed more than two years ago by the previous government.

He was confident the money now being poured into mental health and addiction services was making a difference and said the death rate had slowed in recent months.

But he warned New Zealand could not afford to become complacent in case another crisis was to happen.

Detective Inspector Scott Beard said police were boosting education about synthetic cannabis and the harm it caused.

He said getting it off the streets would take a community-wide effort, including getting any family member who are using the drug to medical help or to call an alcohol drug helpline.

Coroner Morag McDowell is planning to hold a joint inquest into synthetic cannabis deaths to determine what, if any, recommendations can be made to prevent further fatalities. There is no official date set down for the inquest.