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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.
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.
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."
- Martin Johnston of the New Zealand Herald