The hotly contested issue has seen anti-legal high protesters take to the nation's streets, and addicts forced to travel further afield for a fix as councils clamp down on local retailers.
However, opinions are sharply divided on whether to ban legal highs completely.
The Government says banning synthetic cannabis products would not work because once one is banned, another with different chemical combinations will spring up in its place.
One addiction expert says banning legal highs would not force people to change habits, while another wants a ban because of the harm caused by the products.
Crime victim advocates the Sensible Sentencing Trust says the Government is "apathetic" and has unfairly passed the buck to councils to stamp out the problem.
Mayors say legislation limiting where legal highs can be sold and banning individual products shown to cause harm is not enough.
Some call for an outright ban, while others are lobbying MPs to strengthen regulations.
Legal high laws
Following public outcry over the sale of legal highs at corner dairies, Parliament introduced the Psychoactive Substances Act in July last year, which passed by 119 votes to one, with only Act MP John Banks opposed.
It allowed synthetic recreational drugs to be sold legally if they can be shown through scientific testing to have only a low risk of harm.
Under the act local authorities can develop a locally approved products policy (LAPP) to determine where legal high products can be sold, but cannot completely ban the products' sale.
Associate Health Minister Peter Dunne, responsible for introducing the bill to regulate legal high sales, says the act's impact has been "dramatic".
In an open letter to the Northland Age last week [April 16] Mr Dunne said the number of outlets selling legal highs had been reduced from around 4000 to just over 150; the number of products being sold had fallen from about 300 to 41, and sales had been restricted to persons aged 18 and over, with no advertising or promotion permitted.
So far only the first phase of the act has been introduced, which limits which retailers can stock legal highs, tightly controls product advertising, and grants interim licences to approved retailers to sell a product until it is proven unsafe.
However in 2015 the next phase of the act kicks in, forcing product owners or manufacturers to prove a product is 'low harm' before it can be sold.
A spokesman for Mr Dunne said the act's second phase provisions could prove too expensive for people to produce substances that met the act's conditions.
Once the second phase came in, all current licensed products - 41 - will have to be withdrawn and new products would have to be deemed safe under the act.
Councils' response
Five councils have so far implemented LAPPS, and about 22 others are working through draft policies.
In Hawke's Bay, Napier City Council's plan came into effect late last year and Hastings has since followed suit.
However unlike Hastings, which was able to temporarily force the closure of its two last legal high retailers, Napier has been unable to shift one last remaining retailer, Adult Selections, because the store meets all the conditions of the council's LAPP.
Council staff say based on CCTV footage showing foot traffic heading into the store, customers could be spending up to $7500 a day on legal highs.
Hamilton City Council has responded to pressure from residents and adopted a psychoactive substances policy late last month which placed strict restrictions on legal high retailers - forcing them to operate at least 100m from sensitive sites including churches, schools and community facilities.
The policy forced the temporary closure of existing retailers - which had their licences suspended by the Ministry of Health - and addicts were forced to travel to nearby small town Te Awamutu to buy products.
Tauranga City Council is facing mounting community pressure to follow Hamilton's example, and has come up with proposals for tough restrictions on retailers including forcing them to pass on customers' personal information and keep records of customer purchases.
Customer records would then be forwarded to the police or Ministry of Health, to be kept for seven years.
Legal highs industry organisation the STAR Trust responded to the Hamilton ban by announcing it would take the council to the High Court to seek a judicial review of the policy.
The trust is also planning an appeal against the Hastings closures.
STAR Trust research manager Angela McInerney says North Island mayors calling for prohibition "goes against all the scientific evidence that proves prohibition does not create better public health outcomes".
"As mayors are not informed by science and research, instead moral panic and uneducated ideas, they are not adequately informed to make these decisions."
War of words
Peter Dunne is unapologetic about the Government's stance, and blames mayors for their "inexplicable tardiness" in implementing LAPPs.
Mr Dunne did not respond to requests for comment, but wrote in his open letter that the Psychoactive Substances Act was developed in response to councils' pleas for the Government to give them local powers to regulate.
"Despite the grandstanding and tub-thumping of the mayors (just before last year's local elections, significantly) nine months later only five of 71 councils have implemented the local plans the mayors said they needed so desperately," he wrote.
"That delay is unacceptable. It is time for them to stop bleating, and start using the tools they implored Parliament to give them."
Napier mayor Bill Dalton, who accused the Government of being "wimpish" on legal highs, says Mr Dunne's comments are "absolutely pathetic".
"Peter Dunne at best is being disingenuous and worst being dishonest when he says that this is all in the hands of councils."
"They have given us absolutely no powers to do anything about it at all and I call on the Government to either have the guts themselves to ban it or to give us the powers to ban the sale of it on our patch.
"All we've got the right to do is push the problem round our city, not to rid our city of the problem."
He wants a complete ban on all psychoactive substances, with exclusions for prescribed drugs and those already controlled by other legislation such as alcohol and tobacco.
Local Government New Zealand president and Hastings mayor Lawrence Yule says legal highs are having a "devastating effect" on communities.
He gives the Government "full credit" for cutting down legal-high outlets, but says media hype surrounding the issue has generated a new wave of interest in the recreational drugs.
Police and hospital emergency departments are seeing users suffering ill effects from products currently on sale, which are supposed to be safer than those removed from the market, Mr Yule says.
He disputes Mr Dunne's assertion that mayors have been tardy.
Councils that have not yet implemented LAPPS are being cautious, keeping an eye on how the Hamilton and Hastings appeals develop.
"The councils that have [implemented LAPPS] are now finding themselves in a very interesting legal space that's going to need to be tested."
About 80 per cent of mayors would support a total ban on legal highs, but others support strengthening regulation, he says.
Mr Yule and several other mayors have been meeting Mr Dunne and other MPs to achieve constructive solutions.
Medical evidence
Community Drug and Alcohol Services clinical director and psychiatrist Dr Susanna Galea says addiction services, mental health professionals and emergency departments are still seeing a lot of harm from legal-high products, even with the act in place.
Symptoms can be severe, including psychosis, irritability, dependence - which is hard to treat - strong anxiety and even seizures.
It is different to a natural marijuana dependence because synthetic products are "much more potent", causing more serious adverse effects.
She advocates a ban on products causing harm to users, but says in theory the act should work if products are required to be proven low-harm before being sold. "We're seeing quite a lot of harm, so I would want those substances linked with that harm off the market."
She is encouraging doctors to report patients' adverse reactions to specific products to the Centre for Adverse Reaction Monitoring, to get those products off the market.
