It said that higher usage in developed countries could be due to increased pain management for cancer in ageing populations and for other chronic illnesses.

It comes as the national drug regulator, the Therapeutic Goods Administration, faces great opposition to its interim decision to stop codeine products, including common painkillers like Panadeine and Nurofen Plus from being available over the counter, to prevent people from misusing and growing dependent on them.

The TGA delayed its final ruling on this until next June after it received an "unusually large" number of submissions, mostly opposed to the proposed change.

A co-author of the study, Professor Richard Mattick at the UNSW's National Drug and Alcohol Research Centre, said that removing codeine products could make it harder for older and lower-income patients to access the medication they needed but said there was also a risk of harm associated with them. He said the TGA was best placed to make this decision.

By contrast, the study found that there was little change in the use of opioids in most of the world, which "shows a continuing absence of provision of these essential medicines".