Deaths related to codeine, which soon could be available only on prescription, more than doubled in Australia between 2000 and 2009.
There was a jump from 3.5 to 8.7 per million population, with a 9.3 per cent rise each year, say researchers who found the increase mainly driven by accidental deaths.
The second strand of the National Drug and Alcohol Research Centre study covered the circumstances of 1437 codeine-related deaths from 2000 to 2013.
Almost half were attributed to accidental overdose and a third to intentional self-harm.
The study was published in the Medical Journal of Australia on Monday.
The Therapeutic Goods Administration said on Friday that addiction and other risks posed by codeine products are serious enough to warrant them becoming prescription-only medications.
Codeine is increasingly an abused drug in Australia and it can cause severe adverse reactions and is not as safe as other over-the-counter products.
A final decision will be made in November with a view to moving to prescriptions for products such as Nurofen Plus or Panadeine Extra by June 1 next year at the earliest.
The study used data from the National Coronial Information System, but could only reveal trends up to 2009 because records since are not complete.
But as a "snapshot", most of the deaths from 2000 to 2013 were attributed to multiple drug toxicity.
"Those who had intentionally overdosed were more likely to be older, female and have a history of mental health problems," the researchers said.
"Those who had accidentally overdosed were more likely to have a history of substance use problems, chronic pain and injecting drug use."
The accidental deaths may relate to codeine being used to top up prescribed pain medication, or increasing codeine doses or developing codeine dependence, the researchers said.
Strategies to tackle the problem should include patient education and increasing the capacity of specialist pain, addiction and mental health treatment services.
