Another person has reportedly died after taking synthetic cannabis - the eighth death linked to the drug in the past month.

A man in his mid-20s died in Auckland's Middlemore Hospital overnight.

Police said last week that seven people had died this month after consuming synthetic cannabis.

A number of people had also been admitted to hospital in a serious condition.

The Alcohol Drug Helpline has been inundated with calls in recent months about the drug.

Chief executive officer Andrew Slater said there had been a 100 per cent increase in calls relating to synthetic cannabis between April and June this year, compared to the same period last year.

The Herald revealed yesterday that the life-threatening reactions to synthetic cannabis are being blamed on some of the drugs being home-made, using toxic chemicals including weed killer and fly spray.

Avondale Police area prevention manager Acting Inspector Marcia Murray said many users didn't realise the toxic chemical cocktail they were smoking.

"That's the troubling thing, it is an illegal drug, and it is extremely dangerous, because we just don't know what's going into this product.

"Any drugs that we seize, we get them tested. What comes back are the technical aspects, which show things like fly spray and weed killer."

Murray said the Avondale police had some good results with synthetic cannabis busts in April and June, leading to 12 arrests.

But she said police needed the community's help to crack down further.

"The most concerning thing is I wonder whether people realise what they're putting into their bodies, and the fact that it is extremely dangerous.

"They're putting their lives at risk.

"We need to know who is actually dealing these, so we can shut them down. And the community needs to know how dangerous they are, and not to purchase or use them."

People need to tell us, even anonymously, who is supplying these drugs so we can get them out of our communities and keep them safe.

"Wellington emergency medicine specialist Dr Paul Quigley said Hutt Valley Hospital was regularly having to treat users of synthetic cannabis.

He said a single smoke of synthetic was equivalent to 15 normal joints.

"This is why the effect is so very different and so very dangerous."

"Synthetic cannabis is one of the more dangerous products around and is responsible for some immediate health harms."

He said the drugs could cause epileptic seizures, heart palpitations, kidney problems, significant anxiety, insomnia, and worsen mental health conditions until they reached the level of psychosis.

"Because synthetic cannabis is so much more potent than natural cannabis we were also seeing the effects related to substance abuse and addiction developing rapidly," Quigley said.

"Users would need to smoke regularly every 3-4 hours, even waking during the night to smoke."

Middlemore emergency medicine consultant and toxicology expert Dr Chip Gresham said they were seeing dangerous side effects, including life-threatening seizures.

"Occasionally we get new brands or batches that come through, and whatever new batch or brand that's out there is putting people's lives at risk by causing seizures and other serious medical problems.

"The bottom line is this. People are getting very sick from whatever new synthetic cannabis is out there.

"It is critical that people understand that even if they have used it many times in the past, this new brand or new batch can be life-threatening."

Gresham said if someone smoked synthetics and began to feel strange or unwell, they needed to seek medical help urgently.

The deaths have prompted the Chief Coroner and police to issue a public warning about synthetic cannabis.

Chief Coroner Judge Deborah Marshall said the seven dead are believed to have used synthetic cannabis recently or were found with it on them.