More than 20 untested brands of synthetic cannabis are now legally on sale and likely to stay on the shelves well into next year.
Drug users on online forums have described some of the products, which sell under brand names such as Anarchy, Voodoo and White Rhino, as "extremely potent" and warned users to be careful with the amount they take.
The Ministry of Health has defended the temporary approval of the drugs, saying they appear to be relatively low risk and will have to pass stringent tests if they are to go on sale permanently.
The drugs have become legal for now under the Psychoactive Substances Act, which came into force two months ago.
The new law banned sales of synthetic drugs from dairies and other convenience stores. It allows sales from specialist shops if makers can prove their products are low risk, but the regulations setting standards may not be ready until next year.
In the meantime, the ministry is allowing 107 retailers to continue selling 28 brands of drugs - all apparently variations of synthetic cannabis - until scientists can determine what the tests should be.
Drug makers and sellers will then have a month to decide whether they want to apply for a full licence and three months to make the application. Manufacturers are expected to have to pay millions of dollars to cover the cost of testing each drug.
Massey University drug researcher Dr Chris Wilkins said he had been contacted by international colleagues who were amazed that New Zealand appeared to be legalising such powerful, untested drugs.
"There's a lot of stuff there that I wouldn't expect to make it through a real regime test."
Dr Wilkins said there was a strong incentive for the drug industry to sign up for interim licences as the fee for each drug was only $10,000.
"I've talked to some legal high manufacturers who say that if you keep that licence for three months ... you could earn hundreds of thousands of dollars.
"So it's a bit of a no-brainer to go for the interim licence even though when the new regulations fully come in, you haven't got much intention of taking it any further because you know that it's not going to make it."
Medsafe group manager Dr Stewart Jessamine, who is leading the changeover to the new system, said the ministry had assessed the drug applications as low, moderate or high risk and not all had passed, even on a temporary basis.
Asked if some manufacturers could be taking advantage of the interim licences, he said the ministry was trying to show good faith towards the industry and expected the same in return.
"The act gives us the power to investigate and revoke licences if we come across information that indicates people have not told us the truth or are continuing to undertake activities that are not permitted by the legislation."
One of the advantages of regulating a previously illegal drug trade was that approved retailers valued their legal status and were more willing to tell the authorities about other businesses who they believed were breaking the law.
Dr Jessamine said the ministry planned to introduce importing regulations in a few weeks, which would cover the active ingredients used in the drugs.
A code of manufacturing practice would follow in a few months but full regulations - including the scientific tests used to decide if a drug was low risk - might not be ready until early next year.
Dr Jessamine said no one knew whether the overall market for synthetic drug sales had shrunk since the new law banned dairy sales in July, partly because illegal selling remained unmonitored.
The ministry's best guess was that about 1000 dairies had been selling synthetic cannabis before the law change. This was supported by data from one medium-sized supplier that used to sell in up to 400 outlets.
Now, just over 100 monitored specialist shops were involved.
Drug designer aiming to market legal cannabis pill
Party pill king Matt Bowden is back in business with a government licence to make and sell mind-altering drugs.
Mr Bowden - who has introduced substitutes for methamphetamine, Ecstasy and cannabis to New Zealand in the past decade - has gained a temporary licence as a retailer, importer, manufacturer and researcher of drugs under the new Psychoactive Substances Act.
His firm, Stargate International, aims to start selling a new legally approved cannabis pill next year and to build a "world-first" factory on the North Shore for production.
Spokesman Grant Hall said the pill would be branded as 4:20 (cannabis sub-culture code for a user) but sold in sober packaging to avoid accusations of youth marketing.
He predicted it would be less harmful than current smokeable products, which produce carbon monoxide and other toxins.
The company has tested the pill at a relatively mild 1mg strength on volunteers under medical supervision. Some took several pills but suffered no medical side-effects apart from an increased heart rate and "having a good time", Mr Hall said.
Stargate was also planning to produce a synthetic cannabis vaporiser, similar to a marker pen. Users could press a button to get a hit and pass it around in a group.
However, Mr Hall said Stargate did not plan at this stage to reintroduce any drug similar to Ecstasy. It wanted to start with products that were as simple and low-risk as possible, especially as it was expected to cost about $180,000 just to apply for approval to start the expensive tests.
Mr Bowden became the face of the designer-drugs business in the early 2000s, pioneering the introduction of drugs such as BZP and later Kronic in NZ . In the past few years, he has toured the world as "Starboy", his rock star persona.