Small numbers of Kiwis are still getting their hands on synthetic cannabis and other psychoactive substances, despite a three-year-old law that banned them from sale in New Zealand.

Of the 1395 New Zealanders who took part in the latest Global Drug Survey, 4.8 per cent (66 people) said they had used novel psychoactive substances - a group which ranges from herbal smoking mixtures to potent hallucinogens and even deadly opioids - in the past year. The global average was eight per cent.

A further 0.37 per cent of Kiwis (five people) said they'd used synthetic cannabis in the past year, a third of the global average of 1.1 per cent.

CAMERON BURNELL/FAIRFAX NZ Drug Foundation Executive Director Ross Bell is concerned about people getting 'mysterious white powders'.

The drugs include the hallucinogen NBOMe and synthetic cathinones or "bath salts" - both of which have sparked serious health scares in New Zealand in recent years.

READ MORE: Full NZ results from the 2017 Global Drug Survey

Mark Tantrum Associate Health Minister Peter Dunne says there was a stockpiling of 'pretty nasty and awful' products before a ban took effect.

In 2015, a Christchurch man spent a week in a coma after nearly dying when he took NBOMe, while a Kapiti man last year died after taking the cathinone Alpha-PVP - the same "zombie drug" which featured in a shocking video that circulated on Facebook this year.

Most Kiwis said they were buying products in stores - suggesting the novel psychoactive substances they're using are generally quite harmless.

However, 6.8 per cent said they'd purchased from a dealer, while 11.4 per cent were buying online. Many were also obtaining the products from friends.

Drug Foundation executive director Ross Bell says a huge number of products banned under the three-year-old Psychoactive Substances Act are still "illegally available" in New Zealand.

"There's a smorgasbord of new chemicals on the New Zealand black market - bath salts and synthetic cannabis products. People [think they] are buying ecstasy, and it's a whole lot of unknown cathinones, alternatives to ecstasy.

"We're really concerned because what people are getting now is mysterious white powders. Even synthetic cannabis products often come as a mysterious white powder, rather than as plant material. So in any given week, you don't know what your mysterious white powder is."

Data from Customs shows seizures of items regulated under the Psychoactive Substances Act dropped considerably in 2015, before again rising last year, while seizures of "unknown" substances have skyrocketed.

However, MDMA Mimics - which include synthetic cathinones - fell in 2016.

It appears Alpha-PVP may have run out of steam in the New Zealand market: in December, police began testing wastewater in Auckland and Christchurch for drugs, and found no sign of Alpha-PVP, though hundreds of grams of methamphetamine, MDMA and cocaine were identified.

Bell says it appears someone in Wellington may have had "a batch" of Alpha-PVP in the past few years.

"It could be that that's gone," he said.

Wellington Hospital's own encounters with the drug suggest so.

"We had a very short exposure to Alpha-PVP, which was very concerning, with highly disordered patients coming requiring chemical sedation and significant physical restraint," emergency medicine specialist Dr Paul Quigley says.

"We had one likely death from an Alpha-PVP overdose from hyperthermia and multi organ failure."

The hospital had also seen a recent cluster of ethlyone presentations, with patients suffering palpitations and anxiety, though Quigley adds that it sees about one drug presentation for every 100 involving alcohol.

Looking ahead, Quigley was particularly concerned about Kiwis putting themselves at risk from fentanyl products bought on the dark web.

The opioid drug has sparked a crisis in the Canadian city of Vancouver, where it was linked to 139 overdose deaths in January and February alone.

In New Zealand, Quigley says, "this will potentially have fatal consequences, whereas in reality 99 per cent of all the other drugs around are not 'deadly'."

DRUG LAW WORKING, DESPITE CONTINUED USE

Survey organisers attributed New Zealand's "very low rates" of synthetic cannabis use to the older average age of respondents - 42 - and their higher socio-economic status: 80 per cent were in paid employment; 47 per cent had a university degree or higher qualification.

But they added that the Psychoactive Substances Act - which took all synthetic cannabis products off shelves in 2014 - had "no doubt" contributed to declining usage.

"What strikes me as being quite amazing is that given the fact it's so difficult to get drugs [into New Zealand] that there isn't actually a greater use," Global Drug Survey founder Dr Adam Winstock says.

"The fact you're in the bottom half of the graph of people who are using, I think it's great. Your law's worked."

While most products were banned in July 2013, an interim licensing regime allowed several dozen others to be sold until May 2014, before they, too, were pulled from shelves.

Associate Health Minister Peter Dunne says there was "clearly a lot of stockpiling of products that were about to be removed, which were pretty nasty and awful."

He adds that there's been a small amount of "backyard manufacture" in New Zealand.

"It pops up every now and then. The effect is pretty awful, the incidence is pretty small, and the police are largely dealing with it. While there are people getting pretty nasty outcomes, it's not massive."

Psychoactive substances now can't be sold until they're proven safe. That can't currently be done without animal testing - which the government also banned.

No producers have tried to seek licences since. Even if they can one day use computerised testing to prove the products have a low level of harm, Dunne doubts demand will be what it was three or more years ago.

"I think a large part of the attraction of the products at the moment is not so much the risk, but the excitement of trying something new and daring. If you have a product that's certified [as] a low-risk product, I'm not sure that's a great marketing strategy. 'Try our herbal high, it's absolutely no risk' - well, that seems to me to defeat the purpose."

But he warns that there are some 600-odd unknown products in laboratories around the world which may hit the market sooner or later, as well as "other diversions".

"I've heard of people talking about using things like aspirin or common medications or tweaking them in such a way that they could give you a psychoactive effect. Now, if that's the case, that becomes widespread, you're going to need some kind of regulatory environment for dealing with that."