With synthetic highs off the shelves concern is growing users may turn to the black market or make their own drugs to get a kick, Radio New Zealand reports.
The Drug Foundation says users are putting themselves at risk as they do not know what they are buying or what the effects might be.
From 12.01am on Thursday it became an offence to sell, supply or possess synthetic cannabis or party pills.
This opens the door for the black market and potentially unsafe products, with unknown side effects, to be sold in the guise of synthetic cannabis.
Synthetic cannabis begins as an almost potpourri of dried aromatic plants and a chemical is sprayed on the dried leaves.
One Hawke's Bay man says he has heard of people using their own ingredients to make synthetic highs.
"I've heard they use floor cleaners and fly sprays in making their own, so it is not legit stuff... but I've heard what people are mixing up just to make quick, easy money as the government shut the store down and people have still got a habit they've got to control."