A tamper-resistant tablet designed to stop drug users from crushing and then injecting a commonly-abused painkiller appears to be working, a new study shows.

Fewer Australians are injecting a commonly-abused painkiller after tamper-resistant tablets were introduced almost four years ago, a new study suggests.

But there's no evidence the tablets - which are difficult to crush and dissolve so the drug can be injected - has dented Australia's overall opioid abuse problem.

A tamper-resistant formulation of OxyContin was introduced in April 2014, in response to growing concerns about abuse of the prescription drug.

Researchers at the National Drug and Alcohol Research Centre (NDARC), at UNSW Sydney, studied what happened next.

They found that people who injected drugs were less likely to tamper with the new tablets in the pursuit of a big, fast hit, rather than the slow release one that results from oral consumption.

And there was no evidence injecting users switched to other opioids.

"People who injected drugs were using the new formulation much less often. They found it very difficult to tamper with and levels of injection dropped off dramatically and quickly," NDARC Professor Louisa Degenhardt has told AAP.

But there was nothing to suggest the tamper-resistant product had any effect on overall levels of opioid use and harm across the country.

"Given there are so many people in Australia taking opioids - swallowing them as they're intended to be consumed - you mightn't be surprised. There's a relatively small number of people who inject drugs."

Approximately 2.9 million Australians were prescribed an opioid in 2014, compared with an estimated 93,000 people who injected drugs.

NDARC says the study highlights the importance of a multi-pronged approach to tackle opioid use, including making it easier for people to access pain management strategies that don't involve drugs.

Pharmaceutical opioids cause more than 70 per cent of opioid overdose deaths in Australia.

The study relied on drug sales and health data from across Australia, and a cohort of 600 people who misuse prescription opioids, who were followed over time.

The research has been published in the latest edition of The Lancet Psychiatry journal.