There were several types of K2 and he was aware that some stores were still selling the types believed not to contain the banned substances, but he had a simple message for them - "don't take the risk".
Police would be keeping a close eye on what stores were selling and if necessary, would test the products.
"The retailer is taking the risk that the products they are stocking don't contain the two chemicals. If they do take the risk and we find their products do have these banned chemicals in them, we will take action," Mr McCullough said.
"I've heard some horror stories from parents about their kids who have taken it, about their erratic behaviour, violence, psychosis and fits. We are supporting those stores that are showing some social responsibility and refusing to sell these dangerous products."
He said the money made from selling synthetic cannabis products was obviously very good, but he urged retailers still selling them to think about the social consequences and the other potential risks.
"They are making themselves a target for burglars, and we've had burglaries that have targeted these products."
He said they are in direct competition with the gangs, who control the illegal drug trade and may not take kindly to the competition.
"We are also hoping customers vote with their feet and go to places that don't stock them," he said.
Northland medical officer of health Clair Mills said the synthetic cannabis products were a major health concern. "These things have an impact on young people's brains and as there is no labelling on them to indicate what is in them, people really don't know what they are taking.
"They have some quite nasty, long-term side-effects."
Mr Dunne said the latest ban is another blow to the legal high industry and leads up to the "killer punch" with the Psychoactive Substances Bill becoming law.
The Health Select Committee is due to report on the bill to Parliament mid-next month. The bill will restrict the importation, manufacture, and supply of psychoactive substances and only allow the sale of psychoactive substances that can meet safety and manufacturing requirements.