Legal highs approved for sale are being linked to vomiting, hysteria and numbness.
Calls to the National Poison Centre reveal people have suffered seizures, severe kidney failure and "running around madly" after smoking synthetic cannabis.
Many of the more severe reports are linked to now-banned brands, such as K2, Kryptonite and Kronic.
Other bad reactions involve brands given interim approval by the Ministry of Health for legal sale, including AK47, which one person said left a niece hysterical and gasping for breath.
However, most reports simply record "synthetic cannabis" as the offending drug.
The reports were released by the ministry under the Official Information Act, and cover this year until August.
The manager of the ministry's Psychoactive Substances Regulatory Authority, Dr Donald Hannah, said most of the reported ill-effects were linked to now-banned brands and coincided with a surge in publicity around tighter restrictions.
Reported ill-effects after smoking approved brands, such as Anarchy and AK47, were minor and did not justify banning them outright, he said.
Law changes imposed in July have restricted the sale of legal highs to specialist shops, with only brands proved to be "low risk" granted interim approval to be legally sold.
The interim licences were short-term while the ministry developed a more rigorous testing regime.
However, the released report showed that calls to the poison centre rose after the restrictions were imposed, with a spike in July and August.
The poison centre said that, in August alone, 31 people reported "adverse clinical effects" from synthetic cannabis, including comas, aggressive behaviour and psychosis.
Some legal highs had also been licensed despite no clear information about what chemicals they contained.
"Products that have been approved for legal sale have descriptions that are meaningless."
There was also uncertainty among officials about how to classify new psychoactive chemicals being used in synthetic cannabis, some of which were completely unknown.
Poison centre toxicologist Leo Schep said legal-high brands have been approved despite known links to bad reactions and unidentified ingredients.
However, the ministry was doing its best to assess the risk with limited information and unknown chemicals, he said.
"At the moment, we don't know. We have these products approved for sale but we just don't know what is in them."
Paul Quigley, emergency medicine specialist for the Capital & Coast District Health Board, said there had been a decrease in people admitted to emergency departments after smoking synthetic cannabis since the restrictions were imposed.
While there appeared to be fewer, less dangerous, products available, that did not mean all approved legal highs were safe, he said.
"It is still ‘buyer beware' out there, even if we are in a better position than we were."
- Fairfax Media
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