Synthetic cannabis has been described as "madness juice" by a senior police officer who says its popularity has contributed to increasingly violent attacks on police.
Waikato and Bay of Plenty Police Association regional director Wayne Aberhart said the legal highs favoured by many young teenagers made them braver, often causing them to become aggressive and physically violent.
"Synthetic cannabis that's just madness juice. [People using it] are hard to subdue. That is a concern for our officers at the moment," he said. "It just seems to have the effect that people just don't listen to any sort of reason whatsoever. I suppose it's like P."
Figures show the total number of physical assaults on police officers in the Western Bay of Plenty decreased from 101 in 2010 to 89 last year but the use of weapons increased from two to six.
Mr Aberhart said assaults were becoming more brutal.
"The level of violence in them is probably increasing. We are dealing with a higher number of people on drugs, particularly P.
The level of violence is probably higher. "It is a concern. It's a concern for wives and partners and it's a concern for parents of officers more than the officers themselves."
His comments come as NZ Lotteries announced it was taking a stand against synthetic cannabis and yesterday announced it had asked all of its retailers to stop selling legal highs from July 1.
Mr Aberhart said he knew of 13 and 14-year-olds who used synthetic cannabis every day.
It was so readily available and made people unpredictable, he said.
"I had one parent say to me the other day that he used to smoke cannabis and he'd rather his kids smoked cannabis than K2 because K2 just makes them unpredictable. They can't even be dealt with by their parents."
Mr Aberhart worried about what effect the drug would have on young users in a few years time. He feared the legal highs would badly damage their brains, which continued to develop throughout the teenage years.
Internal Affairs Minister Chris Tremain and Associate Minister of Health Todd McClay supported the move by NZ Lotteries to ask their retailers to remove all synthetic cannabis and party pills from sale.
"The sooner psychoactive substances are out of shops the better. New Zealanders are extremely concerned about what these products are doing to the health of our young people. This is a community issue and I am pleased to see Lotto making a firm stand on it," Mr Tremain.
"Selling these substances is not compatible with the sale of lotteries products. Profits from NZ Lotteries are returned to the community to help fund recreation, arts, community projects and sports. K2 and party pills have been linked to serious health effects and anti-social behaviour, including crime and violent offending."
"It is important to protect vulnerable people in our communities. The Psychoactive Substances Bill is currently before the Health Select Committee which is due to report back shortly. I hope to see the Bill progress quickly through the house," says Mr McClay.
Mr Abernathy said NZ Lotteries' stance was "excellent" and hoped other retailers would follow suit.
"It would be refreshing for others to follow NZ Lotteries. Why would you peddle something that's not natural and has negative effects on people? They don't do anybody any good."