The law change - to be introduced to Parliament under urgency next week - spiked Labour's guns. It was poised to propose its own ban on psychoactive substances amid increasing protests from local communities to the harm legal highs caused.
"I'm just thankful something is finally happening," said Sherilyn Tasker, whose 21-year-old son has suffered from the extreme effects of synthetic cannabis use and spent time in a mental health ward. "The ban finally allows him to get off it for good. As it has become progressively harder to get a hold of, he has used it less and less. I'm sure many other people are in the same situation," Ms Tasker said.
"There are a lot of parents out there ripping their hair out over this and a lot of ignorant people unaware of the massively detrimental effects of these products. I see it as far worse than alcohol and marijuana."
Read more of the Herald's legal high coverage this morning:
Mixed reaction to legal high ban
For one couple raising their grandchild, the news brought hope. "I am glad," said Ray Hira. "Now we may have a chance to save our 16-year-old grandson, who has been on it for two years."
One South Auckland community is contemplating a neighbourhood celebration of the law change.
Hunters Corner Town Centre Society chairman Pat Taylor said a store that sold the substances attracted criminals and young people who were begging or prostituting themselves to raise money for the drugs.
"It's very welcome news. We have a wonderful community in Hunters Corner and we might have a celebration once the legal-high shop has disappeared from our community."
More than 250 products were banned in August when the Psychoactive Substances Act, promoted by Associate Health Minister Peter Dunne, came into force. But 41 products had temporary approval for sale until the testing regime was introduced.
Mr Dunne said the remaining synthetic products will be stripped from shelves until they can be assessed by a Ministry of Health-backed testing regime. This meant all synthetic cannabis and party-pill brands would be removed from the market "for some considerable time - and some will never come back".
"I think that the reason we didn't include those 41 products initially was that they hadn't been identified as problematic," said Mr Dunne.
"The public concern of recent weeks has led me to revisit that question and I've been working on the legislation for some time now."
Labour leader David Cunliffe, who had planned to announce his party's policy in Mangere this afternoon, welcomed the decision but called it "an admission of failure" by the Government.
Mr Dunne said he had long planned an amendment but had not wanted to reveal it until Parliament resumed because it could lead to stockpiling and "panic-buying".
Policy announcements by Labour and New Zealand First had "forced his hand", he said.
Auckland Mayor Len Brown said communities had made it clear that they wanted immediate action, and the Government measures were "a strong step forward".
The legal-highs industry, however, is in uproar, saying about 150 outlets nationally will be affected.
Shosha, which has three stores in the Auckland CBD and another in West Auckland, said 60 per cent of its sales involved legal highs and banning them could kill the business.
Drug Foundation chief Ross Bell said the Government's ban would have negative consequences.
"We've been here before. Historically, what happens in these situations - and I absolutely guarantee it will happen now - is that there will be fire sales, people will stockpile, and the risk with that is people might consume too much."
He also warned that products would make their way onto a criminal blackmarket and the Government would have to manage people who had become addicted to drugs that were no longer legally available.
Asked whether he was expecting protest from manufacturers, Mr Dunne said: "I don't really have much of a view about their concerns. I'm more concerned about getting the regime that we put in place last year working effectively."
The ministry's testing regime is expected to be similar to pharmaceutical drug trials. It could cost manufacturers more than $1 million to get a single product approved.
Synthetic copies much stronger than real thing
The legal highs to be banned by the law change are mainly synthetic copies of cannabis, but they tend to be stronger than the real variety.
The Health Ministry website lists 42 psychoactive drugs, including the brands Apocalypse, Amsterdam Havana Special and Jungle Juice, that have interim approval. They gained that status under the legislation passed by Parliament last year that aimed to ban the sale of legal highs unless proven in clinical trials to pose no more than a "low risk" of harm.
The psychoactive ingredients in some of the 42 products include "AB-Fubinaca" and "CL-2201".
Toxicologist Dr Leo Schep, of the National Poisons Centre, said the psychoactive chemicals in synthetic cannabis tended to bind more effectively than the real thing to receptors in the brain, making them much more potent drugs.
The drugs are associated with a range of potentially serious physical and mental harms: rapid heart rate, agitation, seizures, psychosis, hallucinations, acute kidney injury, heart attacks and strokes. Dr Schep said: "What I've seen a lot recently, particularly in those who want to get off it ... is nausea, vomiting, diarrhoea and abdominal pain. I've noticed in the last month or two severe and persistent vomiting, to the point, sometimes, they are vomiting blood ... they can't keep fluids down, they can't keep food down."
In the first three months of last year, one in every eight patients admitted to Dunedin's acute psychiatric ward had been using the synthetic cannabis K2.
- Martin Johnston