A bad batch of opium responsible for the serious lead poisoning of several Australians was likely imported from Iran, the NSW government says.
Australian border officers, federal police and state health departments are on alert after two people were poisoned in Victoria earlier this month.
Another opium user in western Sydney was hospitalised in April.
A NSW Health spokeswoman told AAP on Thursday it was likely the opium was imported from Iran where there's been a spate of lead poisonings since 2016.
"Significantly elevated blood lead levels can cause long-term organ damage or be fatal," the spokeswoman said.
Opium is a dried material extracted from the opium poppy but, unlike other opiates, doesn't undergo further chemical refinement or processing.
A letter was sent to Victorian emergency departments late last week warning staff to be aware of potential cases of lead poisoning.
"The opium is suspected to originate from overseas but was purchased locally and is in the form of a dark resin/paste," the letter obtained by AAP stated.
Experts say there are two ways lead can find its way into opium.
One theory is that it's used in the production process. The other is that it's deliberately introduced into opium because drugs tend to be sold by weight.
Two Iranian men in January were charged with smuggling $16 million worth of opium into Melbourne inside part of a roadworks machine.
Authorities discovered 12.4 kilograms of opium resin in the base of the asphalt compacting machine which arrived by air from Turkey.
