Australia's ban on over-the-counter codeine has dramatically reduced the number of overdoses and cut sales of the painkiller in half.

The first peer-reviewed research to investigate the effect of the switch to prescription-only codeine in February 2018 has vindicated proponents of the controversial decision.

The monthly rate of codeine overdose calls has more than halved since patients have needed a doctor's prescription to buy any product that contains the opioid, according to the analysis by NSW Poisons Information Centre data, which fields 50 per cent of all poisoning calls in Australia.

When it came to low-strength codeine (up to 15 milligrams), the drop was 79 per cent over the first 12 months following the rescheduling, the research team from the University of Sydney and University of NSW found.