Australian Border Force officials have made several seizures of a dangerous new substance called W-18.
Authorities have issued a grim warning over the street drug, which comes amid a new wave of deadly painkillers emerging around the world.
Australian Border Force boss Roman Quaedvlieg said the dangerous drug is "even more potent than fentanyl", an opioid medication so potent it's been nicknamed "Drop Dead" because a tiny amount of it can be fatal, The Daily Telegraph reported.
Fentanyl was also the drug that sparked a huge scandal in the Victorian ambulance service a couple of years ago, after it was found to be disappearing from paramedics' kits.
"We are finding small incidents of fentanyl being seized at the border. It is a highly potent form of opiate, which is coming into this country," Mr Quaedvlieg said.
"When I spoke to our counterparts in US and Canada recently they said we should be aware of it, and I commissioned some research and found, as well as our detections, there is evidence from state and territories police and number of coronial inquiries supporting this."
But what exactly is W-18, and where does the real danger lie?
WHAT IS W-18?
Contrary to popular belief, W-18 is not an opiate drug.
Created by a team of Canadian lab researchers in the early 1980s, the drug was researched as an analgesic and intended as a non-addictive painkiller.
Nowadays it comes in both pill and powder form, and cannot be detected in the bloodstream.
Since emerging on the grey market, subsequent research has found it has little or no affinity to the opiate receptor.
Adjunct Research Fellow with the National Drug Research Institute Dr Stephen Bright told news.com.au that W-18 is just one of many dangerous new drugs that are cropping up.
He described it as a depressant, as opposed to a party drug, and said it's most likely those who used it would believe they were actually taking heroin.
Many media reports have claimed the drug is "100 times stronger than fentanyl" and "10,000 times stronger than morphine", but Dr Bright disputes these claims.
"It's absolutely untrue," he said. "We don't know the actual dose of it. People are buying it as heroin, and that's the real danger, because they're likely to die if they think it's heroin.
"W-18 is just one of hundreds of these new opiates and other drugs that are being designed to be used as counterfeits. In the last 12 months, we've seen a significant increase in the drugs being sold as heroin."
This, Dr Bright said, is a big part of the problem. People are dying because they don't actually know what they're taking, which can greatly increase the risk of an overdose if luck isn't on your side.
"If you go back 20 years, everything was more clear - heroin was heroin, MDMA was MDMA, and so on.
"The situation now is we have thousands of these new drugs that are being sold as traditional drugs. Heroin could be fentanyl. Heroin could be W-18. It could be U44770. We don't know."
As an example he pointed to the United States, where carfentanyl, a drug with similar qualities to fentanyl, has been showing up on the streets.
"Here's what scares me: we're now seeing carfentanyl being sold in the US," he said. "That's 100 times stronger than fentanyl - and that's a fact. It's used on animals. It's used to take down elephants. The amount of the reversal agent required for humans is six times that of a heroin overdose."
Dr Bright isn't the only expert to challenge popular claims about what W-18 is and isn't.
Earlier this year, the Canadian government's health department issued a news release that warned against the highly potent drug.
It said the drug was a synthetic opioid that is "extremely dangerous and can be 100 times stronger than fentanyl".
Bryan Roth, a pharmacology professor at the University of North Carolina who is researching the drug, told the Calgary Herald there is no concrete evidence regarding the strength of the drug.
"It could be a dangerous drug. We don't know," he said.
"As far as I have been able to determine, there's no scientific data on the compound, other than this single patent. And in the patent, it's really impossible to determine much about the compound, other than that it has pain-reducing activity and it is more potent than morphine."
WHERE DO THESE DRUGS COME FROM?
It is believed that the drug now derives from Chinese labs where less common drugs are mass-produced and sold online as "traditional" drugs.
The drug will then be illegally exported overseas, where cartel-linked drug operations will dilute it with everything from heroin to baby powder before distributing it.
Given they are typically manufactured in homemade drug labs, the contents and potency of the final "product" will vary from batch to batch.
But because it's so potent, it's easier to smuggle than other drugs in a compact size.
Dr Bright said the situation is only made worse by the basic economics of illegal drug manufacturing, which he described as the "iron law of prohibition".
"When a drug is prohibited, manufacturers look for drugs that are active at lower dosages since this makes them easier to smuggle," he said. "If it's active at a lower dose, you need less of it.
"When it comes to heroin, drugs such as fentanyl have a similar effect, but are much more potent and cheap to produce. It makes economic sense for people to import these chemicals and sell them as heroin."
WHAT NEEDS TO BE DONE?
Dr Bright warned against "fear-based campaigns" and said Australia needs to place a greater focus on drug checking and harm minimisation.
"What I think it highlights is the need for better early-warning detection centres, so that we can get the information as quickly as possible," he said.
He pointed to the Netherlands' policy of harm reduction, where testing services for consumers guarantee anonymity and legal protection to donate samples, describe what they believe it is, and get test results on what it actually contains.
"If implemented here, this system would give us unparalleled data on the nature and characteristics of the discrepancies between expected and actual drug composition," Dr Bright said.
"Combined with forensic testing of police seizures, this monitoring data would allows us to see changes in the drug market and respond rapidly."