Kronic and other synthetic cannabis will be pulled from New Zealand shelves within weeks - but manufacturers claim the move to ban their products is short-sighted and will be futile.

Urgent legislation going before Parliament today will allow all 43 current synthetic cannabis products to be classed as "temporary controlled drugs" and withdrawn from sale.

Associate Health Minister Peter Dunne will have the power to place products in the category, which would ban them for 12 months.

During that time, a product would be assessed by a committee - appointed by Mr Dunne - which would judge whether it was safe to be sold.

Articles in the Herald have highlighted an increase in the number of people seeking medical treatment after using synthetic cannabis, and the aggressive marketing of the drugs to young people.

Mr Dunne told the Herald medical professionals' reports on the harm synthetic cannabis caused made him doubt the drugs would be sold in New Zealand again.

But Zaid Musa, of manufacturer Enjoi Products, said that although products could be quickly banned, they could still probably be on the market for at least a month before being detected and pulled.

"This is not the end of the legal high industry in New Zealand. There's always ways around it; there are always loopholes."

That was supported by the co-owner of the Hemp Store in central Auckland, Chris Fowlie, who said it would take some time before authorities noticed new products.

Matt Bowden, who imports the chemicals used to make Kronic, would not comment directly on what the industry might do in response to the ban.

"But you are aware as I am of ... the futility of banning drugs."

Mr Dunne said he thought the ban would be "pretty belts and braces".

"The timeframes are so tight. In each case it's seven days. So if products are reformulated, I'll just do the same thing over and over again."

Synthetic cannabis has been made and sold in New Zealand for about 10 years, but use and sale of the R18 products were low-key until recently.

Very little is known about the short-term or long-term effects of smoking the chemicals used in synthetic cannabis.

In July, screening by Environmental Science and Research (ESR) revealed that two products illegally contained a prescription sedative.

Mr Dunne was criticised after he opted against banning the products following a report by the Expert Advisory Committee on Drugs in March.

But yesterday, he said he believed he had now found a way to remove the drugs from sale.

"While I can understand the public clamour for action and to just get on and ban it, it's not quite that simple, I had to get it right."

Mr Bowden predicted the move would push about 500,000 users of synthetic cannabis to buy genuine cannabis on the black market.

The Herald understands people will not face charges if found with a small amount of a banned synthetic cannabis - which the industry says will lead to stock-piling.

Massey University senior researcher Chris Wilkins said the banning of BZP-based party pills showed what the effect of banning synthetic cannabis would be.

Forty-nine per cent of men aged 20 to 24 had used BZP-based pills in 2006 but since their ban, use of legal substitutes had been minimal.

Mr Dunne said the bans were a stop-gap measure until the Government considered a Law Commission recommendation to require the industry to prove its products were safe.

But the Law Commission recommendations were "high level" and it could be a challenge to determine the "safety" threshold for products such as Kronic.