Use of the potentially addictive painkillers oxycodone and fentanyl is rising in regional Australia, the latest analysis of drugs in wastewater has shown.

The analysis of 54 wastewater sites by the Australian Criminal Intelligence Commission found that while methylamphetamine, commonly known as ice, remained the most commonly used illegal drug, prescription opioid use in regional areas outstripped 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 report, released on Thursday.

Regional Queensland and parts of Tasmania and Victoria had the highest overall usage rate 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 Australian federal government announced last year that painkillers containing codeine would 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 were legally prescribed by doctors for intense pain, they were open to abuse.

In terms of illicit drugs, the report found ice usage has plateaued in the past year, while cocaine and ecstasy use appears to be declining, possibly thanks to big drug busts by police this year.

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 New South Wales and the Australian Capital Territory 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.

NSW recorded the highest rates of cocaine and ecstasy use. “Unlike methylamphetamine, capital city areas on average had higher cocaine use than regional centres,” the report said.

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

The report’s findings were based on wastewater samples collected from 54 sites between April and August and then tested for 14 substances to help create a snapshot of national drug consumption.