Metonitazene is more potent than fentanyl. Photo: Supplied / High Alert
A dangerous opioid linked to drug-related deaths in North America has been detected in New Zealand for the first time.
The organisation High Alert said metonitazene has been found in a yellow powder, probably from crushed tablets and could be in circulation nationwide.
It says the drug acts quickly to produce a strong sedative and depressant effect.
The substance could be selling as isotonitazene, oxycodone or an unspecified opioid.
Sarah Helm from the Drug Foundation said it is causing concern.
"This is a particularly potent opioid, which is a type of metonitazene and it's reportedly been sold in the Wellington region.
"It's possible it's actually been sold as oxycodone or some other prescription opioid."
Helm said just a small amount can cause overdoses and it has been responsible for deaths in the United States.
Fentanyl test strips cannot detect it.
Helm said the yellow pills are unusual because their potency is so variable.
"It could be that there's little bits of higher potency within the pills, and so if you take one piece of the pill and you're fine, it might be that there's another piece that's a heck of a lot more powerful.
"We're sort of comparing it a little bit to a chocolate chip cookie if you like, so there's little bits of more potent stuff within it."
High Alert has urged people not to take any yellow powder or yellow tablets.
"Metonitazene has a potency greater than fentanyl," High Alert said on its website.
"These tablets/powder have an unknown dosage and taking them could lead to serious harm, including death."
Twelve people were hospitalised in Wairarapa earlier this year after fentanyl was detected.
High Alert said those who take the drug could experience severe nausea, sweating, slowed breathing, cold and clammy skin, pinpoint pupils and loss of consciousness.
"A lethal dose of metonitazene is equivalent in size to a few grains of salt, meaning there is no way to accurately dose this substance," High Alert said on its website.
If anyone took them and started to lose consciousness or breathe slowly, 111 should be called immediately.