Banned synthetic cannabis blends are unlikely to be back on shelves because attempting to prove they are safe could cost millions of dollars.
A Ministry of Health discussion document obtained by the Herald shows manufacturers would likely face a costly process to have products approved.
"By the time you actually launch a product, it's going to cost you over a million dollars to get out there," an industry source said.
The document reveals all ingredients would need to be produced in a facility with "good manufacturing practice" (GMP) certification.
This is to ensure dosage did not vary dramatically from batch to batch, which had been recorded in BZP party pills and reported by some synthetic cannabis users.
"To have something like that, it's going to cost millions ... There are not many places in New Zealand which are GMP to start with," the source said. "And then you have to go through a clinical trial which can take up to two years."
Kronic and other products were pulled off shelves last year after the Government urgently passed the Misuse of Drugs Amendment Act.
The bans are a stop-gap measure while the Government drafts a law that would put the onus on manufacturers to prove their products were safe before they can be sold.
If products pass pre-clinical toxicology and good manufacturing requirements, human clinical trials would be likely.
Potential harm to physical and mental health would be recorded, as well as products' potential to cause dependence and withdrawal effects.
A government-appointed regulatory body would then make a final risk assessment of the drugs.
As well as data from the pre-clinical and human trials, societal implications of approval - such as users' impairment while driving - would be assessed. Finally, if a product was deemed safe for sale, it would likely face advertising and sale restrictions similar to those on tobacco and alcohol.
Yesterday Peter Dunne, the Associate Minister of Health, said the new regime was "on track" to be introduced this year. "The temporary class drug notices can be extended as required for another 12 months if they are going to expire before the permanent legislation is in place."
Mr Dunne would not comment on the possible details of the approval process for psychoactive substances.
"However, I remain committed to a strong regime that protects young New Zealanders and puts the onus of proving their products safe back on to producers and distributors."
The proposed approval process for synthetic cannabis blends will require:
* Pre-clinical toxicology data, including animal studies.
* Manufacturing quality requirements.
* Data from human clinical trials.
* A final risk assessment of the product.