A deadly synthetic drug more potent than heroin has been detected by Australian scientists in US wastewater for the first time.

Protonitazene is a type of synthetic opioid that is extremely dangerous and even small amounts can lead to possible life-threatening toxic effects.

It's three times more potent than fentanyl - a drug 50 times stronger than heroin - which has led to an alarming number of overdose deaths across the US.

University of Queensland researchers analysed wastewater samples from eight locations in seven US states - Arizona, Georgia, Illinois, New Jersey, New Mexico, Oregon and Washington.

In Illinois and Washington, levels of protonitazene were found in the wastewater.

"The protonitazene found in Illinois wastewater was at a level below the quantification limit of our instrument, but the wastewater from Washington contained protonitazene at approximately 0.5 nanograms per litre," Dr Richard Bade said.

Dr Bade said the discovery was concerning.

Several overdoses in the US have already been linked to protonitazene.

Protonitazene was detected in South Australia, Queensland, Victoria and Western Australia in 2023 after health officials reported it was being mixed with other illicit drugs.

Two South Australian men were treated for overdoses suspected to be a result of protonitazene.

The death of an Adelaide man and two deaths in Queensland were investigated by coroners for their relation to the dangerous opioid.

Synthetic opioids, like protonitazene, were developed in the 1950s but were never approved as medicines.

Now illegal laboratories are developing dangerous drugs as stand-alone products.

The substance can also be sold labelled as other opioids like oxycodone, heroin, or mixed into drugs like benzodiazepines or cocaine, Dr Bade said.

Dr Bade said the research findings show how important wastewater surveillance was to detecting dangerous drugs.

The research was published in the journal Science of the Total Environment.