A sample of brown powder at Canberra's community testing clinic has been found to contain a dangerous drug.
CanTEST has issued a red alert, warning that the drug carries a high risk of fatal overdose.
The synthetic opioid N-pyrrolidino protonitazene (NPP) is thought to be 25 times more potent than fentanyl.
The drug put tens of people in hospital after being detected in Ireland, CanTEST's clinical lead David Caldicott said on Twitter/X.
"More than 50 patients in five days in Dublin, more than 20 in Cork in six days. It's not even the most potent of the nitazenes," he said.
"This is a dangerous class of drugs, and should be avoided."
Mr Caldicott congratulated the clinic's analysts for detecting the deadly opioid.
N-pyrrolidino protonitazene was first found in the United States in January 2023. It has since been reported in the UK and Oceania.
A report from the US Centre for Forensic Science Research & Education noted the synthetic opioid has the "potential to cause harm" and should be a "high public health concern globally".
The authors advised authorities to implement surveillance measures in communities to track the spread of the drug.
Synthetic opioids are often mixed with other substances such as cocaine and fentanyl, which creates high risks for recreational drug users.
Fentanyl, which is also a synthetic opioid, led to the overdose of more than 73,000 people in the United States in 2022.
