The latest analysis of the nation's wastewater shows a worrying rise in the use of the potentially-addictive painkillers oxycodone and fentanyl in rural areas.

Use of the potentially-addictive painkillers oxycodone and fentanyl is on the rise in regional Australia, the latest analysis of drugs in the nation's wastewater system shows.

The analysis of 54 wastewater sites by the Australian Criminal Intelligence Commission found that while methylamphetamine, or ice, remains Australia's most commonly used illegal drug, prescription opioid use in regional areas is outstripping that in capital cities.

"Consumption of oxycodone in regional sites was well above capital city levels, with the regional national average being almost double that of the capital cities," the commission said in its third national wastewater drug monitoring program report released on Thursday.

Regional Queensland and parts of Tasmania and Victoria had the highest overall users of oxycodone, while in capital cities the highest usage rates were in South Australia and Tasmania.

Usage patterns for fentanyl, a synthetic opioid that is up to 100 times more potent than morphine, were similar, with regional centres in almost every state recording values well above the national average.

"Except for a few sites, regional consumption was substantially higher than capital city areas," the report said.

Medical experts have expressed concern in recent months that more Australians are becoming addicted to pharmaceutical opioid painkillers, following in the footsteps of America which is in the grip of of an opioid epidemic that has caused tens of thousands of fatal overdoses.

The federal government announced last year that painkillers containing codeine will no longer be available over the counter from 2018, in response to growing concerns about addiction.

The commission's report noted that while oxycodone and fentanyl are legally prescribed by doctors for intense pain, they do have abuse potential.

The commission's chief executive Michael Phelan said while the increasing usage rates of the painkillers in regional areas is a major concern, they are becoming harder for people to obtain.

"(What is important) is education particularly for ... doctors with writing prescriptions," he told reporters.

In terms of illicit drugs, ice usage has plateaued in the past year, while cocaine and ecstasy use is falling, possibly thanks to big drug busts by police in 2017.

Ice remains the most common illegal drug in capital cities and regional sites, with South Australia and Western Australia having the highest usage rates, while NSW and the ACT recorded small overall increases in usage.

However, use of ice in Queensland and Western Australia has begun to fall from their historical highs in October 2016.

Justice Minister Michael Keenan said while demand for methylamphetamine has plateaued, it's not time to become complacent.

"We know this drug continues to pose significant challenges for our community," he said.

Elsewhere, use of cocaine and ecstasy was highest in NSW.

Heroin was also included in the commission's analysis for the first time, with usage rates highest in Victoria and the ACT.