A dozen people suffering ill effects after taking Kronic have been seen in Dunedin Hospital's emergency department in recent weeks.

People experienced "significant" adverse effects, including anxiety, loss of co-ordination, dizziness, rapid heart rate and, in some cases, delirium, double vision and psychosis, said Southern DHB medical officer of health Dr Marion Poore.

Twelve people had been seen in Dunedin in recent weeks and it was likely there were other, similar, cases in Invercargill and Queenstown. The side effects might be much worse when synthetic cannabinoid products were used with alcohol, she said.

"Because there is no information on the packet, you really have no idea what you're taking. It's a very high-risk activity."

Dunedin Hospital emergency medicine consultant Dr Tim Kerruish said between two and five people a week turned up at the emergency department suffering side effects from Kronic.

It was unclear whether the rate of people appearing with those problems was worse in the past few weeks.

Those affected were mainly aged between 17 and 25, he said.

It was likely more people were suffering side effects from the products than just those who turned up at the emergency department.

Dr Poore said people should contact a medical professional if they experienced any side effects after using Kronic or any other synthetic cannabinoid product.

The board is also preparing to send prosecution files to the Ministry of Health after two retailers in Dunedin and two in Invercargill sold the restricted product to people under the age of 18 during a police sting on Wednesday night.