Doctors are warning of the dangers of synthetic cannabis after three young people were hospitalised this month with severe kidney injuries.
Canterbury District Health Board said two of the three needed intensive care.
Medical officer of health Alistair Humphrey said side effects from synthetic cannabis range from anxiety, vomiting and headaches to more severe problems like psychosis and heart attacks.
He said the ingredients were often not disclosed by manufacturers, so it was hard to know how to treat patients.
Dr Humphrey said the age of people needing treatment typically ranged from 16 to 22 , but some were as young as 13.
He wants to have synthetic cannabis banned but said at present it was buyer beware.