But under current laws, the Government has been powerless to stop their sale, as manufacturers can rapidly change the chemical formula to get around each new ban.
The law change - originally planned for August 1 but now expected to be weeks earlier - will force drug makers to prove their products are safe before they go on sale. The immediate effect will be that most drugs can no longer be sold but in a few years, some may pass the rigorous tests and become legal.
Medical experts and the legal-high industry are divided over whether the end result will be the world's first legal, regulated drug market - with a line-up of other countries poised to follow - or the tests will be so strict and costly no drugs will get through.
Mr Dunne told the Weekend Herald that the bar would be set high but the testing was not intended to create a de facto ban on all new drugs.
"If products survive that testing regime, then whatever one might think of them personally, it's pretty difficult to prohibit them from being on the shelves in New Zealand."
He said the approved drugs would probably be milder than the synthetic cannabis products that were causing so much concern. That might mean some users turned to illegal drugs for a bigger high but at least the distinction between legal and illegal drugs would be clear.
Mr Dunne said any retailer selling an approved drug would need a licence, similar to a liquor licence, which could be removed if they sold products irresponsibly.
Former party pill king Matt Bowden, regarded as the chemistry brain behind the banned synthetic cannabis products Kronic and K2, has told the select committee considering the bill that his Stargate company is planning a new manufacturing plant to meet the high standards required.
Asked when and where it would be built, he said he needed to see more detail about the testing regime. But with a new psychoactive drug emerging every week, he said, it was vital to make the new approach work.
"If we don't get this right, then things are going to get worse and worse," Mr Bowden said.
Massey University drug researcher Dr Chris Wilkins warned that New Zealand should move cautiously as no other country had tried to create a legal market for psychoactive drugs.
He was not surprised the legal-high industry welcomed the law change - even though most of its products would disappear in the short term - "because this could be a complete goldmine. There's enormous profits available".
Dr Wilkins said the big alcohol and tobacco firms were likely to enter the market once the regime settled down - a claim strongly denied by Lion, DB and British American Tobacco.
"Absolutely not," said Lion communications director Liz Read. "We don't think it would be constructive and we don't think it would be a useful complement to our business."
Getting tough
Under the Psychoactive Substances Bill
• Drug makers will have to prove their products are safe before they go on sale.
• Manufacturers must pay a $180,000 application fee and submit each drug to the same kind of tests used to approve new medicines, including human clinical trials. The process is expected to cost them $1 million to $2 million and take up to two years.
• Drugs on sale now will be banned unless the manufacturer applies for approval under the new regime within a month.
