A dangerous new drug - deadly in doses as small as a grain of sand, is being seized at New Zealand’s border, prompting warnings from police and drug-safety advocates as it takes a hold of overseas markets.

Nitazenes are a strong synthetic class of opioid which can be over 10 times more potent than Fentanyl and hundreds of times stronger than heroin.

They have caused fear across Europe and North America for killing drug-users, and most recently in Australia, where at least 16 deaths in Victoria were linked to the drug.

In 2023 there was one death associated with metonitazene in New Zealand, and authorities have known of the synthetic's presence locally since early 2022.

Customs NZ said there were four Nitazene and three Fentanyl interceptions at the border in the 13-months ending in December 2023, including 268 grams of metonitazene in September.

Despite the relatively few cases, Customs Manager of Intelligence, Bruce Berry said the high potency of the drugs meant they presented a “disproportionately dangerous health risk”.

With the growing threat, the New Zealand Drug Foundation expected the country’s drug market could soon be overwhelmed with the opioids.

“It almost feels like it's an inevitability,” said the foundation’s deputy executive director of programmes, Ben Birks Ang.

The BBC found it was being smuggled into the UK in dog food and catering supplies before being sold on social media.

“It doesn’t take long for our very small drug market in New Zealand to be saturated with other substances,” Birks Ang said, “it may be just one import”.

He said the opioids, which could kill in microgram doses, were often added to drugs like MDMA, cocaine, and methamphetamine and unknowingly ingested by drug-users.

“We could see an increase in deaths, an increase in overdose in New Zealand from people taking [nitazenes] without knowing they’re taking them,” said Birks Ang.

The early warning system for acute drug harm, High Alert had issued four notifications relating to nitazenes, including when it was sold as fake medications like oxycodone and benzodiazepine.

Police say the presence of the drug is low but “of concern” because of how easily the drug could lead to an overdose even among people with “experience using illicit drugs.”

“Police advise no use is best use,” said Detective Inspector Tim Chao, but otherwise encouraged the free drug testing services provided by the Drug Foundation while other mitigation practices were developed.

People can get free nitazene test strips from the Drug Foundation on its website, where it also kept a calendar of nationwide free drug-checking clinics.

Jordan Dunn is a multimedia reporter based in Auckland with a focus on crime, social issues, policing, and local issues. He joined Newstalk ZB in 2024 from Radio New Zealand, where he started as an intern out of the New Zealand Broadcasting School.