Synthetic cannabis users collapse so often after use that slipping into unconsciousness after inhaling the drug is unfortunately seen as normal, a toxicology expert says.

But failing to recognise the person may be losing blood flow to their brain is leading to deaths among users of the drug.

Emergency medicine specialist and clinical toxicologist Dr Paul Quigley has given evidence in Taupo this morning into the death of synthetic cannabis user Andrew Brian McAllister, 49, who died last year.

McAllister's inquest is the first Coroner's inquiry into a number of deaths which occurred in New Zealand last year and were blamed on a stronger-than-usual batch of synthetic cannabis.

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Quigley told an inquest by Coroner Gordon Matenga synthetic cannabis was up to 85 times more potent than natural cannabis and the synthetic cannabinoids in it directly activate receptors in the brain and the heart.

Those often lead synthetic cannabis users to fall unconscious – and it is seen so often that collapse is regarded as normal, with no need to call for help, Quigley said.

It was those strong chemicals hitting the heart and brain of McAllister which caused him to collapse at a Taupo home on August 16, 2017.

He went into heart arrhythmia, stopped breathing and the flow of blood to his brain ceased, eventually causing an irrecoverable brain injury.

Four witnesses, whose names were suppressed, were at the house when McAllister collapsed and said his unconsciousness was normal.

One witness who had seen McAllister smoke synthetic cannabis often, had also seen him zone out, stare into space, dribble and fall over.

McAllister had produced a bag of synthetic cannabis which he had bought earlier and smoked it from a bong before passing out.

"I heard him collapse," said a witness. "I said 'f**k is he all right?' and [the other witness] said something like 'he always does this'.

"Since I had collapsed when I tried synthetics, I didn't think too much of it at this stage."

The witnesses checked McAllister briefly but made no attempt to intervene until some time later, estimated about 20 minutes, when they realised his pulse was weak and he had turned a grey colour.

One person called 111 and began chest compressions until paramedics arrived. He was taken to Taupo Hospital and then flown to Waikato Hospital, where he died the next day.

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

One recounted passing out in a gutter in pouring rain. That experience was enough to put him off.

Another said his legs felt like concrete, he couldn't move, was "s**t scared" and couldn't wait to recover from the drug.

Detective Sergeant Andrew Livingstone of Taupo police said the synthetic cannabis industry was made up of networks of people who imported the psychoactive substances, mixed them with a binding agent such as acetone and then sprayed or used an evaporation method to put it onto a plant material which could be smoked.

The result was an uncontrolled drug and end users didn't know what they were putting into their bodies.

"It's well-known that there's significant money to be made in selling synnies and that the risk is minimal given the penalty," he said.

"We've seen an increase in criminal gangs and networks turning to synthetics to make money.

"Health problems attributed to the use of synnies have increased markedly and in Auckland police have attributed seven deaths linked to the use of synnies."

Livingstone told the Coroner McAllister had a troubled upbringing with a physically abusive, alcoholic father, who had committed suicide when his son was 15.

This affected him deeply and he also began abusing alcohol and using drugs. At the time of his death McAllister was using synthetics almost every day and was a long-time drinker of methylated spirits.

He said police executed search warrants on local addresses where McAllister was believed to have bought the synthetic cannabis 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.

In any case, those spoken to had not seemed to care the drugs were harming people.

"We spoke about what happened to McAllister and there was an indifference from those people as to what they're doing because it's all about the money," Livingstone said.

"There was no expression of any concern or empathy from those people … and that prevented us from going further up the chain in terms of evidence."

At around the same time, Taupo police attended several other incidents where those involved had presented with "extreme agitation" or collapsed after consuming synthetic cannabis, he said.

Just last week, police had attended a job where a mother and father were found in a car "in a zombie state" with a child in the back seat.

McAllister's mother, Margaret, sobbed as she read her evidence recounting her sadness at losing her son. He had gone into drug and alcohol rehabilitation three times but always relapsed.

"He was a good person, a terrific artist. But he was lost.

"He was all mixed up. It was terrible to see him like that but it obviously 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, because it was so addictive."

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

Quigley told the Coroner the synthetic cannabis industry was preying on very, very vulnerable people by doing things asuch as pricing it cheaply so people on low incomes could afford it.

This, combined with a shortage in natural cannabis, meant people were being pushed towards synthetics, he said. It was also by far the most dangerous drug, on a par with opiates.

"There is no way to predict what dose you are getting and that is what makes it so dangerous."

Quigley added it was essential to ensure there was easy access to drug and alcohol rehabilitation services for those who needed it.

The number of deaths provisionally linked to synthetic drugs was about 30 nationally from June 1, 2017 to today, according to Coronial Services.

The coroner has reserved his decision.

Facts about synthetic cannabis

There are no human studies into the effects of synthetic cannabis but it is believed to hit cannabinoid receptors in the heart and the brain, particularly the brain stem which controls functions such as breathing, swallowing, heart rate and blood pressure.

That means users of synthetic cannabis often collapse directly after inhaling the drug because of its effect on the brain stem.

If they cannot be roused by shaking, call for help immediately.

If the person is not breathing, begin chest compressions to restore blood circulation and call 111 for help. Brain injury will begin after only three to four minutes of blood flow being interrupted to the brain.