A coroner has heard how a Taupō man collapsed and died after inhaling synthetic cannabis.

Coroner Gordon Matenga now wants more public awareness around the dangers of synthetic cannabis, particularly the tendency for users to slip into unconsciousness.

Toxicologist and medicine specialist Dr Paul Quigley told the Coroner it was common for synthetic cannabis users to collapse.

In fact it was so common that other people present did not always appreciate that the person was losing blood flow to their brain.

This was resulting in the death of synthetic cannabis users.

Evidence was heard in the Taupō District Court on May 28 into the death of Andrew Brian McAllister, 49, who died in August.

McAllister was a regular synthetic cannabis user.

Quigley told the inquest synthetic cannabis was up to 85 times more potent than any chemical in natural cannabis.

"The people manufacturing [synthetic cannabis] do not understand the potency," he said.

"When inhaled, it quickly gets into the brain, hits the brain stem and then shuts it down."

He said synthetic cannabis affected the brain stem and appeared to make some people's hearts go into an arrhythmia –which is the case with McAllister, who collapsed at a Taupō home on August 16, 2017.

McAllister went into heart arrhythmia and stopped breathing. Because no blood was flowing to his brain, this caused an irrecoverable brain injury.

Four witnesses, whose names are suppressed, were at the house when McAllister collapsed and all said the same thing – that it was normal for McAllister to collapse after taking a hit of the drug.

One of the witness said they had seen McAllister smoke synthetic cannabis often and had seen him dribble, stare into space, fall over, or zone out.

When arriving at the Taupō house, McAllister apparently asked for a bong and produced a bag of synthetic cannabis. One of the witnesses offered him a regular cannabis joint, but McAllister refused.

After taking a hit of the synthetic cannabis, he passed out.

"I heard a crash," said a witness. "I looked inside and saw him on his back and [another witness] said he always does this.

"I had collapsed when I had tried synthetic cannabis, so I didn't think much of it."

The witnesses checked on McAllister briefly but continued to carry on with what they were doing.

About 20 minutes later, one of the witnesses noticed McAllister was changing colour and another witness thought he was dead.

"I gave him mouth to mouth. I'm not trained in CPR and I've never had to do it before."

Chest compressions were given until paramedics arrived. He was taken to Taupō Hospital and then flown to Waikato Hospital, where he died the next day.

All four witnesses recounted their own experiences with synthetic cannabis. Three of the four had only tried it once and said they couldn't move, felt sick and delusional and were scared they were going to die.

One said his legs felt like concrete, he was "s**t scared" and was praying to God, while another described how he collapsed in the gutter in the pouring rain and couldn't move for what felt like hours.

McAllister's mother, Margaret, couldn't hold back tears as she read her evidence, recounting the day she lost her son.

As McAllister was an alcoholic, Margaret said he had tried rehabilitation three times before but he always relapsed.

She recounted how on the morning McAllister collapsed, she heard him rattling around in the house but he was gone before she got up. At 11am, she got a phone call from Taupō Hospital saying they had picked her son up and his heart had stopped for 15 minutes.

Margaret said McAllister was "all mixed up" and she never knew what he was on half the time.

"It was terrible to see him like that that, obviously it just affected his brain that way. He would come around and want $20 to buy some smokes and I would say 'are you sure it's just for smokes?' and he would say 'I'm sure' but it was just for another fix I guess."

But she also said she remembered the good.

"He had been a good son. He was a good person. A terrific artist. All that is lost now."

Margaret said she tried reaching out for help for McAllister, but there was nothing available and he would have had to have seen a psychiatrist first.

Detective Sergeant Andrew Livingstone of Taupō Police said during the investigation, they executed search warrants on addresses they believed McAllister could have bought the synthetic cannabis from but no direct link was found to any person who had supplied him with the drug and no one could be held criminally liable for his death.

Livingstone said while conducting the search warrants, there was no extension of concern or empathy from the people involved and that had prevented them going further up the chain in terms of evidence.

He said there was significant money to be made by selling synthetic drugs but the risk was minimal given the penalty. They've seen an increase in criminal gangs and networks turning to synthetics to make money and Auckland Police have attributed seven deaths linked to the use of synthetic drugs.

Livingstone told the hearing McAllister had a troubled upbringing due to a physically abusive, alcoholic father, who committed suicide when McAllister was only 15.

Being hit hard by that, McAllister also began drinking and using cannabis. At the time of his death, McAllister was using synthetics almost every day and was a long-time drinker of methylated spirits.

Livingstone said there needed to be a focus on education around synthetic drugs and McAllister's background could be seen as an insight into dependence on those kind of substances.

Quigley told the coroner that what they did know was happening in New Zealand, was that the synthetic cannabis industry was "preying" on very vulnerable people. It was cheap so low income people could afford it and it was targeted into the cannabis market when there was a shortage.

Quigley explained how the manufacturers get plant material, like tobacco, and then place the synthetic chemical on it in one of two ways; hand spraying it from a bottle or heating the chemical in an oven with the plant material, turning it to steam before letting it cool down and cover the product.

While Coroner Matenga reserved his findings until a later date, he and Quigley agreed that more education needed to get out about synthetic cannabis use, especially the way people could collapse.

Quigley said it was not normal for people to collapse after taking a synthetic drug, but if they did, people should shake them hard to wake them. If they do not wake up a call for help should be made immediately.

If they are not breathing, start chest compressions to restore blood flow to the brain. There is only a three – four minute window before a brain injury appears.

- Stuff/ STEPH RANGI