The use of synthetic cannabis is concerning Rotorua officials who say those who smoke it become aggressive and can experience psychotic episodes.
One synthetic cannabis product in particular - K2 - is causing concern among police and health officials.
K2 is available in some stores in Rotorua which are known to sell other synthetic cannabis products and herbal highs. It has an age restriction of 18.
Rotorua residents have been turning up at the city hospital's emergency department with symptoms similar to those of someone who has used K2.
The head of the emergency department at Rotorua Hospital, Dr Mazen Shasha, said these patients would often arrive in groups, with the most recent being two people about three weeksago.
He said that very often patients would not admit to using synthetic cannabis, especially if they had mixed it with alcohol.
Dr Shasha said both alcohol abuse and using synthetic cannabis products could have the same symptoms.
"Patients usually present with palpitation, nausea, vomiting, not feeling well, light-headed, irritable or aggressive."
His comments came after a Bay of Plenty District Health Board youth alcohol and drug clinician said the drugs had a frightening effect on some users.
Rotorua Police acting area commander Tim Anderson said police were always concerned about any substances which caused harm to the community and children.
He said that was why police prosecuted those selling illegal drugs.
"We are aware that concerns have been raised by the Bay of Plenty District Health Board around the increase in referrals for young people relating to adverse effects experienced from K2," he said.
"We send these synthetic cannabis products away for testing and if any of these are found to be the illegal type then we will prosecute the offenders selling them.
"We have not had any prosecutions yet in Rotorua."
Mr Anderson said drug and alcohol counsellors had reported that typical effects of K2 included psychotic episodes, high levels of aggression, anxiety, hallucinations and general instability.
Te Utuhina Manaakitanga Trust general manager Donna Blair said she was aware of Rotorua youth using synthetic cannabis products.
She said people were curious and the products were legal.
Without naming any particular product, she said she was not aware of any adverse side-effects.
But a Bay of Plenty District Health Board spokeswoman said the mental health inpatient units in both Tauranga and Whakatane had had a number of admissions over the the past month as a direct consequence of people using synthetic cannabinoids, primarily K2.
Associate Health Minister Peter Dunne has said he was concerned by reports of the effects of K2 and the Ministry of Health was working with police to test the product.
Mr Dunne also announced yesterday that legal high manufacturers would face estimated application fees of $180,000 and $1 million to $2 million in testing costs for each product they want to sell, and up to eight years in prison for selling banned substances.
Other changes announced included a $300 fine for personal possession of an unapproved product and a minimum purchase age of 18.
"I make no apologies for setting the bar high on public safety and putting in place a regime with the process costs squarely on the legal highs industry, and not the taxpayer," Mr Dunne said.
The use of K2 made headlines in the United States this year when a 22-year-old man was arrested after he allegedly took K2 and went on a "bad trip".
The man assaulted his neighbour then got on his hands and knees and began barking and growling like a dog.
He said the man then turned his rage on his flatmate's dog and choked it before "ripping pieces of flesh away and eating them".
The packaging for K2 has no listed ingredients and no name or contact for the manufacturer.
